# Oil light/ABS Light



## Eremon1 (Jan 8, 2009)

I have a 96 Oldsmobile Cutlass Supreme 3.1 V6 Automatic. Recently had problems with the starter and Vehicle Speed Sensor which have been solved. Since owning this car the 'Low Oil Level' Light and the ABS light have been on. The oil light often goes out after some time driving and the oil level is physically okay on the dipstick. The ABS light came on after a few months of owning it and it used to come and go but now it seems to stay on all the time. Brakes seem ok.

Any ideas?


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## mack1 (Nov 27, 2007)

Hi Eremon1 and welcome back,

I know nothing at all about oil level sensing. Maybe someone with experience in that area will jump in and help.

I have a 96 S10 blazer and have worked on it's ABS unit. That year, GM was using mostly Kelsey-Hayes ABS systems. Likely yours is that brand. Two wheel sensors and the vehicle speed sensor are used by the unit to know if a wheel(s) is locked and will respond by stopping foot pressure to that wheel(s) and releave pressure to it, thus stopping the locked condition. The most normal failure is one of the sensors, two wheel sensors and the Vehicle Speed sensor. You just replaced the VSS, so we can count that one out. There is three brake fluid pipes from the ABS unit. One for each front wheel and one for both back wheels. The unit can control each front wheel, or both back wheels as needed. (With front wheel drive, yours might be different) 

96 was the first year that they passed the wheel speed sensors to the PCM and it sent the signal on to the ABS electronic controller. Prior to 96, the ABS was a "stand alone unit". The PCM also drives the ABS light on the dashboard for the first time. If the lamp is removed from the instrument cluster, the PCM, in it's infinite wisdom, will turn on the brake lamp instead (you won't find that anywere in the books). 

Google Kelsey-Hayes to find lots of info on that system.

The wheel sensor are of the magnet/wire wound type similar to the VSS sensor. They look at metal teeth on the inside hub of the wheels. The sensor wires can be easily found entering the hubs. 

Check the wheel sensors and let us know what you find.

Very best regards,
Mack1


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## Eremon1 (Jan 8, 2009)

Okay, this morning while driving I attempted to pass a slow car. When I accelerated to passing speed I noticed a small sound like a bump or something and the engine light came on. After this it was rev-ing real high to get from standing still until I got to about 20Kmph. Then is seemed to shift normally. When I got home I checked the fluid level it seems to be okay. I looked for leaks and saw nothing. After it cooled down it seemed to be working normal. Now when I drive it, it seems normal accept when I try to accelerate too much, then it seems like the tranny is slipping.

I'm no expert, but usually if a clutch or something has gone bad, it stays bad right? Why would this seem to come and go? When I turn on the heater the engine temp comes down a bit and the car doesn't seem to act up as much...


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## Eremon1 (Jan 8, 2009)

Anybody have any ideas?


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## Eremon1 (Jan 8, 2009)

Okay scratch the last problem posted. I let the car sit for a day and then drove it again. After about 4Km the engine light went away. I'm driving the car as nicely as I possibly can.

I'll keep you posted on the ABS sensor issue when I get the chance to take a good look at how and exactly where the sensors are located. If it's as easy as the VSS was to change out then I shouldn't have a problem.


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## Volt-Schwibe (Jan 12, 2003)

Eremon1 said:


> Okay, this morning while driving I attempted to pass a slow car. When I accelerated to passing speed I noticed a small sound like a bump or something and the engine light came on. After this it was rev-ing real high to get from standing still until I got to about 20Kmph. Then is seemed to shift normally. When I got home I checked the fluid level it seems to be okay. I looked for leaks and saw nothing. After it cooled down it seemed to be working normal. Now when I drive it, it seems normal accept when I try to accelerate too much, then it seems like the tranny is slipping.
> 
> I'm no expert, but usually if a clutch or something has gone bad, it stays bad right? Why would this seem to come and go? When I turn on the heater the engine temp comes down a bit and the car doesn't seem to act up as much...


I'm going to say this sounds like a torque converter solenoid has had a problem. It may have become stuck, and sitting unstuck it, but i can't be sure. In those newer cars the torque converter is computer controlled, and when you passed that car, the transmission went through a sequence of adjustments, in the tightness of the converter lock-up state, as well as the sensativity of the shift. So if you had an engine light, as well as something you could hear/feel, followed by the feeling of the transmission slipping, i'm pretty sure this is a torque converter problem. There is a small chance an accumulator piston has failed inside there, causing first gear to slip, especially if it seems to have no problems in any gears other than 1st. 

I'd say this one needs a shop, where some guages can be applied to it as it's run through a couple simple tests. Without those guages, there's not alot any mechanic could do, aside from just opening it and checking each part.


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## mack1 (Nov 27, 2007)

On the ABS issue, there is some more info that I forgot to mention. The light came on when you had problems with the VSS sensor, as it should. It didn't go out when you replaced the sensor. That could be normal, as a scan tool will clear all but the ABS, and the PCM itself will clear the other lights. At dealerships, they have an expensive scan tool that will turn the light off, but they will charge you for that. If there is an actual problem with the ABS, it will come back on. 

Your ABS might be functional, even with the light as nothing has extinguished the light. 
If ok, but just a light, others have taken their vehicles on a dirt road and done some slide stop menovers that cause the ABS to function. Once it functions, it will clear its own light. It's worth a try.

Best regards,
Mack1


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## Eremon1 (Jan 8, 2009)

Volt-Schwibe said:


> I'm going to say this sounds like a torque converter solenoid has had a problem. It may have become stuck, and sitting unstuck it, but i can't be sure. In those newer cars the torque converter is computer controlled, and when you passed that car, the transmission went through a sequence of adjustments, in the tightness of the converter lock-up state, as well as the sensativity of the shift. So if you had an engine light, as well as something you could hear/feel, followed by the feeling of the transmission slipping, i'm pretty sure this is a torque converter problem. There is a small chance an accumulator piston has failed inside there, causing first gear to slip, especially if it seems to have no problems in any gears other than 1st.
> 
> I'd say this one needs a shop, where some guages can be applied to it as it's run through a couple simple tests. Without those guages, there's not alot any mechanic could do, aside from just opening it and checking each part.


Thank you. That makes sense to me. It went away yesterday while driving and hasn't come back so far. Right now I'm being very easy on it while driving. I've been trying to keep in under 3500 RPMs through the shifts. The car is running fine at the moment. I think you're right, the best thing to do is to have the computer scanned for the codes to help pin-point the problem(s).

@Mack1
The ABS issue was actually a few months before the VSS. During that whole problem I was assuming that the ABS was somehow related, but the light was on months before the VSS failure and is still on now. The brakes seem ok, I don't get any vibrating during normal driving as I would expect. In the winter when I'd hit a patch of ice or something I remember the TRAC light coming on and I'm sure the pedal-vibe was there at that time. I will try the dirt road idea.

Just to make sure I have the idea correct, I basically drive to a speed and then press the brake hard enough to try and lock the tires, while still maintaining control? This should activate the ABS which should then reset the light if it's a false error or old code?

*I forgot to mention* That the ABS light is on when the car starts most of the time. But sometimes it isn't on when the car is started and even for a moment of driving. Same with the oil light, sometimes it's not on at car startup. Usually when it was recently driven tho. And it goes out after some time driving.


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## mack1 (Nov 27, 2007)

The ABS does a selfcheck when the ignition switch moves from off to on. If all is OK, it turns the lamp off. If it comes on when the car starts moving, it means one of the sensors is not sending signal to the unit. Again the three sensors are on two wheels and the VSS. 

In order to test ABS, the sensors have to send abnormal signals to the unit. One or two wheels locked or slow while the other(s) is turning normally, and of course, the break pedal must be pressed (not the park brake). If you lock all four wheels, then you may, or may not get the unit to energize and try to control the brakes. 

Best regards,
Mack1


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## Volt-Schwibe (Jan 12, 2003)

Usually 25 mph is enough to produce a lock up skid. If you want to try at an even slower speed, try it in a wet parking lot at 15 or 20, or on gravel or dirt. You shouldn't have to slam on the brakes at a crazy high speed, just any speed high enough to cause all 4 wheels to slide. (the skid doesn't even have to last more than a second or two for the brake system to realize it's in a full skid)

But, mash the pedal fairly hard, or you might not get all 4 wheels at the same time.

I've seen people successfully reset their ABS system this way, it is definately something that should be written into the repair manuals.


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## Eremon1 (Jan 8, 2009)

Volt-Schwibe said:


> I'm going to say this sounds like a torque converter solenoid has had a problem. It may have become stuck, and sitting unstuck it, but i can't be sure. In those newer cars the torque converter is computer controlled, and when you passed that car, the transmission went through a sequence of adjustments, in the tightness of the converter lock-up state, as well as the sensativity of the shift. So if you had an engine light, as well as something you could hear/feel, followed by the feeling of the transmission slipping, i'm pretty sure this is a torque converter problem. There is a small chance an accumulator piston has failed inside there, causing first gear to slip, especially if it seems to have no problems in any gears other than 1st.


Also, I'm not having trouble with first gear, it's all the rest of them that sometimes seem to go to sleep along with the speedometer. I just replaced the VSS with a used one from the wrecker and I also have another one. Could it be a faulty VSS or something else?

Okay, the engine light has been off since that one day. The car drives mostly normal if I keep the RMPs down to 2000-2100 Max. When the car warms up if I try to accelerate much faster than that, the speedometer goes funny, sometimes all the way to 0 and the tranny feels like its in neutral. Then if I let off the gas I can sometimes get the speedometer to pop back up and then the car will drive sorta normal, but for the most part once this happens I have to let the car sit for a half hour or more and it is ok again. I was talking to somebody at work about this and they said it could be the trany-filter is clogged. 

Could a clogged trany-filter be causing this type of issue?

If so, is this something that can be replaced in the back yard?


Also, regarding the wheel speed sensors. I've been looking around for info as my Haynes manual doesn't seem to cover that info in any detail and I've found conflicting information. Some sources say all four wheels have a speed sensor and others say it's only in the front wheels or back wheels. 

Now my question about that is, if my wheel sensors are causing my ABS light to come on, could they also be affecting the transmission in some way?


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## Eremon1 (Jan 8, 2009)

I also have been doing some reading on the Vacuum Modulator Assembly. Apparently if this fails or there are vacuum line problems then the transmission can exhibit odd behavior including slipping and shifting problems. What are your thoughts on this Mack1?


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## mack1 (Nov 27, 2007)

Actually, I'm not good with transmission problems and I leave it to others to respond. I've noticed that others have had lots of problems with transmission solenoids, but mostly on Dodges.

Going back to the oil level sensor....Did you mean oil pressure? I recall that oil pressure is required for the PCM to keep the engine running, at least on some later models. I don't know how the PCM would respond to an erratic oil pressure signal. See if you can clear that up and see what else works better. I'm still not convinced that the VSS sensor which measured so close to the original one was the total fix for your first problem. I like sensors that measure bad if they are bad, or at least some distance from norm. 

Best regards,
Mack1

edited...I'm thinking of an oil pressure switch, not pressure sensor.


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## Eremon1 (Jan 8, 2009)

Fair enough on the transmission. I think I should start a transmission thread because for now this issue is more important to fix than the ABS or Oil light problems which seem to be sensor issues.

For the oil, it's simply a light called Low Oil Level. But I've checked, checked and rechecked the oil and the levels are fine. I've heard other say this happens commonly after oil changes but I'm not familiar enough with the sensor system there. I believe it's located somewhere in the oil pan but I haven't taken it apart. I'm not a fan of playing around with gaskets unless I really have to. I've also heard some things said about the low oil level indicator pointing to a bad oil pump. Any thoughts?

As for the VSS. I hear what you're saying, but I've got three of them and the one bad one and they all seem to measure about the same. Perhaps the methods of testing I've used don't produce accurate results.


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## Volt-Schwibe (Jan 12, 2003)

I'm starting to think that these problems are all relating to the ECM module.

1. You have a speedometer problem, anytime you attempt to goose it.

2. You have a weird transmission problem, which shows symptoms in parallel with the speedo problem. The ECM controls most of the activities inside the transmission in these newer cars. Because the ECM controls these parts, the problem would seem to be caused by one of these parts, even though that part might be fine.

3. The oil light stays on regardless of actual oil level. This could be related to a bad pump, pushing a low pressure, but that depends on if this vehicle uses pressure to check level, or actual oil level in the pan. (your book should answer that) Alternatively, on these GM cars, especially oldsmobile, a rare issue can happen where the oil doesn't get changed for a 50,000 mile time period, and the oil can gum up certain passageways, causing a low pressure signal to the sending unit. (the test for this is to remove the sending unit, and apply an actual guage, and run the engine to about 2000 rpms in neutral, the fix for it, would probably be a complete tear down and cleaning, or some sort of endoscopic cleaning procedure)

4. The ABS light is on, and as mack1 said, the VSS signals are translated through the ECM module on these years of GM vehicle.

Anyhow, the one thing that connects all these problems is the ECM. Perhaps it's getting poor power signal, or perhaps it's not getting clear signals from all it's remote parts, but it would seem to me that something is seriously wrong here, and the only clear link i see between all these problems is the ECM. Maybe check to see that it's getting strong power, also check ground. Check all your connectors from the ECM all the way to the parts that are misbehaving, and remember, this problem could all be caused by one single connector, because on these ECM controlled vehicles, there's a few sensors that set the bar for the others, so if one sensor isn't working right, then a whole bunch of others will be interpeted incorrectly, seeming like problems with all those parts, when it's one single part that is bad. (or not firmly connected)

It could be that all these problems have simultaneously developed, but it's starting to make me think the ECM is failing.

I wish i could help more, I have a friend i can ask to read over this thread tomorrow, maybe he'll have some insight that i don't.


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## Eremon1 (Jan 8, 2009)

Volt-Schwibe said:


> I'm starting to think that these problems are all relating to the ECM module.
> 
> 1. You have a speedometer problem, anytime you attempt to goose it.
> 
> ...


Okay, I was thinking that is a possibility but the thing that has me confused is the intermittent nature of the problem and how it seems to be around the time the car gets to peak operating temperature. I know there is gunk in the rad when the orange and green types of coolant were mixed at some point. I'm wondering if there is a coolant flow problem to the trany. Also I've been hearing an odd sound coming from the area were the vacuum modulator assembly sits. I've heard that if the VMA fails or doesn't produce the correct vacuum then this can cause the transmission to exhibit odd behaviors in shifting.

If it is the ECM, can I pull and old one from the wrecker and pop in straight in or do I need a scanner to retrain the computer after the ECM swap?


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## Volt-Schwibe (Jan 12, 2003)

On something as old as 90's, as long as it had the same engine and transmission, then no retraining would be required.

Also, the coolant does not flow into the transmission, it's the opposite, transmission fluid flows into a tank _inside_ the radiator tanks, and cools down when it contacts the metal, which is contacting the radiator coolant, and then back to the transmission. It's very rare for these lines to get clogged up, so unless something has smashed a line down flat, there shouldn't be any problems there.

Unless it really is a clogged transmission filter, which is pretty easy to replace, but you have to drop the transmission pan down, and replace the filter, along with a new gasket. These bolts are problematic if you overtighten them, as it crushes the gasket. There's not usually anything in the way of the pan, so it's usually pretty easy to get it out.

It shouldn't cost more than about 20$ plus fluid to change it, if you decide to go that direction with it.


On a side note, i could swear that they discontinued the vaccuum accumulator in the mid 80's, in favor of a "TV cable".

if your book says you have a vaccuum accumulator as opposed to a TV cable, then it could be something wrong with the accumulator, although the symptoms don't match up all that well.


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## Eremon1 (Jan 8, 2009)

Volt-Schwibe said:


> On something as old as 90's, as long as it had the same engine and transmission, then no retraining would be required.
> 
> Also, the coolant does not flow into the transmission, it's the opposite, transmission fluid flows into a tank _inside_ the radiator tanks, and cools down when it contacts the metal, which is contacting the radiator coolant, and then back to the transmission. It's very rare for these lines to get clogged up, so unless something has smashed a line down flat, there shouldn't be any problems there.
> 
> ...


Well the transmission fluid looks really clean so I doubt it's the filter after all. But it still couldn't hurt to change it and the fluid anyhow.

As for the vacuum modulator assembly, not accumulator, yes there is in fact one there as it states in my repair manual. And it does affect shifts if it isn't working properly. I just don't know exactly how to go about testing it.


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## Volt-Schwibe (Jan 12, 2003)

Because the transmission filter is usually a really fine filter, (5-10 microns) the fluid would always seem very clean, so it's hard to know if the filter is clogged without a pressure test.

As far as adjusting the vacuum modulator, it depends on which transmission you have, but it's normally done with a guage, and then a turn of a screw.

Your book should have a chart showing the different transmission pan shapes, and you should be able to identify which you have from this.


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## Eremon1 (Jan 8, 2009)

Okay that makes sense. I'll get the trany filter/fluid change just to be sure for that. It's cheap enough.

I have the 4T60-E transmission.


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## Volt-Schwibe (Jan 12, 2003)

For some reason i thought we were talking about a rear wheel drive car. Not sure why i'd have thought that since it's a 96.

Being front wheel drive might make it a little harder to get the pan down, but it's still usually not sitting on top of a crossmember.


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## Eremon1 (Jan 8, 2009)

The other thing I forgot to mention in regards to the trany behavior...when driving at city speed and I let off the gas the rpms drop straight to 1000<idle> almost as tho I put the car in neutral. Normally the car would be a higher RPM at that speed until the trans shifted down through the gears. It seems like it doesn't do that properly.


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## Volt-Schwibe (Jan 12, 2003)

That's usually a symptom of the torque converter dying, or the lock solenoid inside it failing. (or the ECM controlling it badly)


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## Eremon1 (Jan 8, 2009)

if that were failing should it not trigger an engine light or fault code in the computer? If that is the problem, it that an expensive fix. This car isn't worth too much but it's the only car my mom has. I'd like to be able to help her out in some way. If I take it to a mechanic I'm afraid of getting "taken for a ride" so to speak...


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## Volt-Schwibe (Jan 12, 2003)

Torque converter solenoid failure should throw a code of some kind to the engine computer, and the engine light should come on at some point, which did happen i beleive you mentioned.

Have you had the computer spit out the codes? I'm curious what codes it's logging.

As far as how expensive, it's hard to say, you might find a good mechanic who can diagnose it in very little time, being able to spit you out a report of some kind which you can use to decide if it's worth it. The shops around here charge 100$ to run the engine computer's codes, and diagnose other things, like fuel pressure and exhaust backpressure, i don't know what kind of deals are offered where you are though. If you could find a quality shop, they should be able to tell with just this 100$ "evaluation" checkup what all is really happening, but make sure and point out up front that you aren't sure you even want to bother fixing it until you know what's wrong, this often helps to remove the dollar signs from their eyes, as they don't want the estimate to be too high, or you'll opt out.


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## Eremon1 (Jan 8, 2009)

Yeah there was the engine light that one day, after that it has since gone away but the problem hasn't. 

I haven't taken it in to get the computer scanned because I was under the impression that some major mechanical faults don't trigger codes.

Thanks alot, that helps me to decide what I should do. Like the idea of taking the dollar signs out of their eyes. I was thinking of doing something like going into a shop as somebody that is looking at the car to buy and am taking it in to get looked over before I buy it.

I guess it's off to the mechanic then so I can get the codes out of the computer. Am I correct in assuming that OBDII codes are standard on all cars these days? Meaning that a particular code in one car with OBDII will have the same meaning for a different car with OBDII...


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## Volt-Schwibe (Jan 12, 2003)

I can't specifically say if all the makers use the same codeset, but, i can say that GM uses the "chevrolet" codeset. This would include your oldsmobile.

"GM cars and light trucks use SAE J1850 VPW (Variable Pulse Width Modulation). The codes here are generally apply to all OBD-II GM vehicles: GMC, Chevrolet, Buick, Oldsmobile, Cadillac, Pontiac, Saturn." 

That's what i've found at this site, which isn't free, but it has answered my curiosity. http://www.obd-codes.com/trouble_codes/gm/

Also, the "i'm looking to buy this car, is there anything expensive that is wrong with it?" is also a good approach to use. It still says to them that they're only getting money for the diagnosis, so they'll tend to be as fair and accurate as possible.


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## Eremon1 (Jan 8, 2009)

Oh yeah there are 5 OBD-II protocols;

* SAE J1850 - PWM
* SAE J1850 - VPW
* ISO 9141-2
* ISO 14230-4 - KWP 2000
* ISO 15765-4 - CAN (Controller Area Network)

That's good to know since I was thinking of just buying the scanner since I think I can get one cheaper than 100$ and then it will pay for itself during the first scan. The one I'm looking at handles all 5 protocols.


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## Volt-Schwibe (Jan 12, 2003)

yeah, one that handles all 5 for less than 100$ would be well worth getting. I need to get me one of those someday, since they stole the paperclip method from me


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## Eremon1 (Jan 8, 2009)

Paperclip method?


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## Volt-Schwibe (Jan 12, 2003)

On the earlier computer controlled cars, there was a connector under the dash you could put a bent paperclip into, and it would flash the codes out the check engine light.

they were really easy to retreive and read, and didn't require any tools.

Dodge had an alternative method, where you turn the key on-off-on-off-on and it would spit the codes out through the light.

I'm not exactly sure when they stopped doing this, but the last few cars i wanted to do it on had no procedure listed in the book for it.


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## Eremon1 (Jan 8, 2009)

I'd wager it happened in 96. That seems to be a big change in the electronic controls for cars in GM anyway. I think the went from the ECM to the PCM and my understanding is that the ECM was very limited in what mechanical parts it controlled. The switch to PCM was a more indept electronics control system which has evolved over time to today's 'heavy on the electronics cars.'

Plus with that upgrade they make you have to buy the gadget to read the codes instead of using your nifty little method.


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## mack1 (Nov 27, 2007)

I think you are right on the 96 being OBDII switchover year. I looked into that when I bought my scanner. I'm thinking the big push to OBDII was for the California polution standards. Seems most of the additions were for EPS things, not for better control of the engine/power train as normally thought. Its never been clear to me that there is a difference in the Engine Control Module and Powertrain Control Module were two different modules. In a given set of prints, there seems to be reference to both, but on the vehicle, there was only one module. On the 96 model, the module had two levels of plugs on the end. Two or three on the top row and the same on the bottom row, making you think there might be two different circuit boards in the same package. 

I've found that the error codes are the same across the vehicle family. GM codes seem to apply to all GM products. Ford code are probably the same, but I'm not sure. That there was a difference between the protocols on American and European Vehicles was pointed out early and most of the scanners wouldn't work on foreign models at that time. Since mine was for my private use, I really didn't care at the time. 

It was scarey that they decided to move to processor control of engine functions. Remember the "points replacement module" that Ford introduced in the late 70's that replaced the $2 points. It failed often and cost about $90 for the module. Hobbyists at the time were building CD (Capacitive Discharge ) systems that would put out thousands of volts more than a normal coil and the points would last for years.....and yes, I built one that never failed. I had three switches that would switch from CD system back to standard coil and points and never had to use it. 

"I've driven cars all my life and never had to call a tow truck until I got one with a computer onboard" said an old gentleman. They do have it down now and I take my hat off to them. We have very accurate timing control through the full range of speeds and torques for both fuel injection amounts and spark timing. That is great. The combination of centrifical and vaccuum advance is no needed on the distributor. You no longer get the extra fuel injected into the engine each time you press the foot feed pedal. Anyone with a nervous foot could use up a lot of extra fuel. I'm not sure I like the idea of controling the transmission shifting using the PCM, the old hydromatic transmissions were actual wonders in their ability to shift at the right time and function without failure for years. Those hydraulic control modules were wonders to behold. If you have ever looked at the hydraulic control module with its many passages and check valves, etc. the word "WOW" has to come to mind. "How did those guys ever design that thing?"

Enough ranting, have a nice day.
Mack1


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## Volt-Schwibe (Jan 12, 2003)

All those passageways and valves more or less equates to a computer. It closely relates to logic circuts, with gates. Pressures (driven by the pump) and inputs (given by the vaccum modulator) calculate down to shift points in some kind of weird physical formula inside a liquid calculator.

It definately is impressive the way they "calculated" things with liquid and pressure.

The best part about them was how someone like me could rebuild one and have it work just fine, without actually even knowing how it functioned. You check measurements and replace bad parts, reassemble and drive it, and it just worked. Now, you need complicated equipment just to even know what little electronic part has failed. But, the overall benefit is well worth it, we can now do more with less power, and it's less expensive than ever before.


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## deezo (May 9, 2009)

THIS IS SOME GOOD STUFF I'VE RESEARCHED ABOUT LOW OIL PRESSURE:

The lubrication system operates by pressurizing the oil and forcing it through passageways in the engine. The oil is pressurized by a pump that’s usually driven by the engine’s camshaft. The pressure in the oil system is commonly called the oil pressure. Just like a person’s blood pressure, an engine’s oil pressure must be maintained
at a certain level. Since the oil pump is driven by an engine component—either the camshaft or the crankshaft—the oil pressure usually varies with the engine speed. An engine’s exact oil pressure also varies depending on its design; however, in most cases, an engine’s oil pressure ranges between 20 and 60 psi. A good rule of thumb is that an engine should have at least 10 psi of oil pressure for each 1,000 rotations per minute (rpm). So, an engine that’s operating at 4,000 rpm should develop an oil pressure of about 40 psi:

10 psi = 1,000
10 psi = 1,000
10 pai = 1,000
10 pai = 1,000
40 psi = 4,000

One of the most common problems in a lubrication system is low oil pressure. As you’ve learned, pressure in the oil system is created by the oil pump. The pump forces the oil through the various engine passageways. As long as the oil can be pumped into the engine faster than it can leak out of the bearing clearances, oil pressure is maintained throughout the system. Therefore, if an engine has low oil pressure, one of the following problems is occurring:

1. The pump isn’t pumping enough oil.
2. The oil is flowing through the engine with so little resistance that
the oil pump can’t pump it fast enough to maintain pressure.

Before you try to determine the cause of low oil pressure, first confirm that the engine does in fact have low oil pressure. As you’ve learned, a typical automotive engine develops an oil pressure between 20 and 60 psi. Many vehicles contain a warning light or gage that indicates if the oil pressure becomes too low. Therefore, the first indication of low oil pressure is usually a lighted warning light or a low reading on the oil pressure gage.

Oil pressure indicators do warn drivers of a problem. However, indicators can’t measure an engine’s actual oil pressure with complete accuracy. The oil pressure may actually be fine, and the indicator may be malfunctioning. For this reason, the first thing that you should do is measure the actual oil pressure in the engine.

The exact oil pressure in an engine can be measured with a special instrument
called an oil pressure tester. An oil pressure tester is an accurate oil pressure gage that can be mounted to the engine. (Purchase an oil pressure tester from an auto parts store). Since every engine is slightly different, the oil pressure tester usually comes with a variety of adapters so that it can be connected to an engine easily. In most cases, the oil pressure gage is connected wherever the oil sender is located. Remember that the oil sender is the sensor device that’s used to operate the oil pressure indicator on the instrument panel. On most engines, the sender is mounted to the side of the engine block near the main oil gallery.

In most situations, the oil pressure sender is unscrewed from the engine and removed, and the oil pressure tester is then threaded onto the engine in its place. Once the tester is mounted into place, the engine is started, and the actual oil pressure can be read on the gage.

Mechanical Causes of Low Oil Pressure:

Once the actual oil pressure is measured, you can begin to determine what the problem is. If you find that the oil pressure is within specifications and isn’t actually low, then the problem is most likely in the oil pressure indicator system and not in the engine itself. The oil sender unit or warning light may be faulty, or an electrical wire may be broken or damaged. However, if you find that the oil pressure is indeed low, the next step is to pinpoint the cause of the low pressure. Low oil pressure can cause severe damage to an engine. In fact, if the oil pressure is very low, you may often hear knocking or tapping noises in the engine. Knocking noises are usually the result of the contact between the crankshaft—or connecting rods—and the bearing inserts. When the oil pressure is very low, there’s no longer a cushion of oil between these surfaces. Light tapping noises in the top of the engine are usually caused by excessive clearance in the valve system, due to a lack of oil to the hydraulic lifters. To operate properly, the hydraulic lifters must have a continual supply of pressurized oil.

Low oil pressure can be caused by any number of mechanical problems in an engine. The most common cause is worn bearing inserts. As the crankshaft and connecting rod bearings wear, the bearing clearances become larger. The oil has larger spaces to flow out of, so the oil flows through the pearances with little resistance. The oil flows out so easily that very little oil pressure is developed. The oil simply leaks out of the bearings as fast as the pump can pump it to them.

Bearing wear also prevents oil from reaching other parts of the lubrication
system. Remember that the lubrication system is a contained system. In other words, if one engine bearing is excessively worn, the oil flows out of that bearing freely, and reduces the oil pressure. This reduction in oil pressure harms the entire lubrication system. When the overall oil pressure is reduced, the other bearings and internal engine components won’t receive the proper lubrication. When the oil pressure is low, serious damage to the remaining engine bearings occurs quickly. The only way to check the condition of the engine bearings is to disassemble the lower part of the engine and visually inspect the bearings.

Bearing wear isn’t the only possible cause of low oil pressure. A worn oil pump may also be the problem. Over time, an engine’s oil pump can wear so much that it’s no longer able to pump enough oil into the engine to maintain the proper oil pressure. Again, to check the condition of the oil pump, you usually need to partially disassemble the lower part of the engine.

Another possible cause of low oil pressure is a leak in the oil pickup tube. You may remember that the oil pickup tube must be airtight in order to work properly. If the tube has a hole in it, or if it isn’t sealed properly to the pump, air could be pulled into the pump instead of oil. This condition greatly reduces the pumping ability of the pump. The end of the oil pickup tube has a screen over it to help keep dirt and debris out of the tube. In some engines, you may find that dirt and debris is actually clogging this screen and preventing oil from entering the pickup tube, and thus, the oil pump. 
In such a case, the low oil pressure isn’t caused by a faulty oil pump, but by the blocked screen. The only way to determine if the pickup screen is blocked is to disassemble the lower part of the engine and visually inspect the screen.

In addition to oil pressure problems and oil leaks, another possible problem that can occur in a lubrication system is a condition of excessive oil consumption. Excessive oil consumption simply means that an engine consumes too much oil and requires frequent refilling. 

As oil is used in an engine, a certain amount of it evaporates under the high heat, leaks out, or is pulled up into the combustion chamber where it’s burned with the air-and-fuel mixture. Oil is splashed up onto the cylinder walls to keep them lubricated. Even though the piston contains an oil control ring, it can’t stop all of the oil from slipping past the piston and entering the combustion chamber. Aslight amount of oil may enter the combustion chamber along the side of the valve stems. A valve stem is placed inside of a valve guide. Since the valve must be able to move freely within the guide, a small amount of oil is allowed to enter this area. The valve seals keep the majority of the oil out of the combustion chamber; however, some oil is allowed past the seals so that it can lubricate the valve guide area.


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## Eremon1 (Jan 8, 2009)

That's great information! Thanks Deezo. I'm not sure if the engine has low pressure or if the 'low oil level' light indicates the level of oil in the system. I know from the dip stick there is the correct amount of oil in the block. The light is always on when I first start the car, but if I drive for a while to warm it up then shut it off/start it back up again the light is off. It will come back if the car sits long enough to cool down.


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