# 2001 S10 4X4 4WD unit not working



## Black Knight

I have the push button 4 wheel drive unit. I tried to put it in 4HI but there are no indicator lights and it feels as if it is still in 2HI. Any idea what could be wrong and how to fix it inexpensively (I'm strapped for cash)? I have instrument lights but no lights indicating which mode it is in. If it is a fuse which one is it? Thanks for any help. I'm no mechanic so please keep it simple.


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## wolfen1086

Step one is check the fuse, its either in the owners manual if you have it, or it should be labeled on the fuse box cover. Yours is definitely all electric, so the fuse is the first place to start.


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## Black Knight

Thanks wolfen I'll check it on my next day off or short day. I'm working 12 hour shifts this weekend.


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## wolfen1086

Your welcome, keep us posted 4WD systems are funny creatures sometimes.


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## Black Knight

I had a chance today to check the fuse in the fuse block on the side of the dash board. It was fine, there was no break in the fillament. I replaced it anyway thinking it might help. No go, the indicator lights are still out.


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## wolfen1086

Ok step 2 is to find out if its the light bulb or something in the system, there are two ways I do it, but I don;'t recommend them to anybody because they are both dangerous as hell and you could be injured or killed doing it the way I do. I'd recommend taking it to a place that can raise it and look at the under side electromechanical system and see whats doing what


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## jaggerwild

Black Knight said:


> I have the push button 4 wheel drive unit. I tried to put it in 4HI but there are no indicator lights and it feels as if it is still in 2HI. Any idea what could be wrong and how to fix it inexpensively (I'm strapped for cash)? I have instrument lights but no lights indicating which mode it is in. If it is a fuse which one is it? Thanks for any help. I'm no mechanic so please keep it simple.


 Might use a test light on both sides of the fuse to see if the 4WD is even getting power to begin with. If you can get to the back side of the switch to also check there, lay under the truck and see if the shifter plug is plugged in even.


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## melarosc

I am seeing the same thing on my 2003 s10. All the LEDs on the dash switch are out. Just stopped working one day. I have verified the switch to be OK. The TCCM (transfer case control module) has all power and ground connections. I read that you can get diagnositic codes out of the TCCM by grounding pin 13 of the OBD connector under the stearing wheel. I did that and still the LEDs on the dash switch do not blink. I think this points to a bad TCCM, but I want some ensurance that this is the case before I lay out $400 for a new one. Anyone have any comments?


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## FanEAW

Pin 13 is the pin use use to ground to check codes.

If you did indeed ground #13 the 4wd light will blink

Code "1" is "RAM standby power" and is considered normal, may be caused by clearing the codes.
Code "2" is "Encoder fault"
Code "3" is "TCCM motor circuit"
Code "4" is "RAM/ROM failure" 

Ground pin 13 at the data connector under the dash. The lights on the switch should flash. You are only going to have a choice of 4 codes as mentioned above. Here is the procedure to further clarify. 

Diagnostic Trouble Code (DTC) Displaying:
The transfer case shift control module is equipped with the ability to store diagnostic information, which is useful to a technician in the event of module, component or wiring failures. This information can be retrieved from the transfer case shift control module by way of flash codes, which are displayed on the three transfer case shift control switch buttons. These buttons are located on the instrument panel to the right of the steering wheel Before obtaining DTCs, perform the following transfer case control module (TCCM) Self-Test. 

TCCM Self-Test 
Observe the transfer case shift control switch indicators while turning the ignition switch to RUN. A properly operating system will flash all indicators and then will return to the current gear. If the system is operating normally, then proceed to Displaying Codes. 
If the TCCM failed the Self-Test, then test the following circuits. 
• Battery Positive Voltage, and Ignition Voltage for battery voltage 

• Ground Circuit for ground 

• Diagnostic enable circuit for an open or high resistance 

• Transfer case shift control switch connector 

If the above circuits are normal but the TCCM still fails the Self-Test, replace the TCCM. 

DTC Displaying 
Turn OFF the ignition for 10 seconds. 
Connect PIN 13 on the data link cable (DLC) to a ground. The DLC is located in the cab under the instrument panel on the driver's side. 
Turn ON the ignition, with the engine OFF. 
Observe the transfer case shift control switch select buttons for flashing codes. Refer to Diagnostic Trouble Code (DTC) List above. 

Important: If the transfer case shift control switch buttons all blink only once and then stop, no fault codes are stored in the transfer case shift control module. 

• When one DTC is stored in memory, that code will blink that number of times followed by a 3 second pause and then repeat. 

• If more than one code is stored, the first code will blink, followed by a 3 second pause and then the second code will blink. 

• This sequence will continue until PIN 13 on the DLC is no longer grounded. 

• If the TCCM will not communicate the presence or absence of DTCs, test the above circuits in Self-Test Step 2. If the circuits are complete, then replace the TCCM. 

Here is a break down of your 4WD system:

1) let's start off with the easy things -- have you checked your fuses? Don't assume that just because the fuses are labeled 4WD that they are the only ones for your 4WD system! Fuse 10 (on the Jimmy/Blazer) is for the courtesy lights but guess what? It also controls the logic side of the TCCM (+5VDC). Pin 6 (thinner orange wire) should produce +5VDC and should be HOT AT ALL TIMES (meaning you should be able to read +5VDC on the line anytime, key on or off). The two large orange wires are your +12VDC lines and are controlled from the 10A fuse located in spot #15. 

Check your LARGE orange wires as you are getting +5VDC logic as the lights are coming on on the dash. The +12VDC is used for the encoder motor, check to make sure you have +12VDC at both the large orange wires (they are right beside each other, and there are two large black wires beside them that are ground).

Notes: All black wires are ground -- all orange wires are power (hot). There is a 10A fuse (#15) for the 4WD system, located in the fuse panel. There is a 20A fuse, located under the hood, that is also for the 4WD system (I'll have to look up the fuse number). The 4WD system also pulls from the 10A courtesy lamp fuse (#10).

2) The vacuum switch (located on the firewall http://www.kylestubbins.com/files/blazer_vacuum_switch.jpg) or vacuum diaphram (located under the battery) could be malfunctioning. The job of these components is to pull on a cable which engages the front, right 4WD hub. I don't think this is likely to be your problem as you should probably hear the encoder motor running (changing the drive mode from 2Hi to 4Hi/4Lo) but there is a sensor on the hub to tell the TCCM when it is engaged, so it could be problem.

3) the encoder motor/module is bad. This is the module/motor that is mounted directly to the transfer case, who's job it is to physically move the gears of the transfer case to put the TC into the various modes (2Hi, 4Hi, 4Lo). You also want to check the wires at the encoder motor as they are exposed to the elements and could be damaged by something flying up under your vehicle (not likely, but possible).

4) The TCCM (located under the passengers kick panel) has wires that are corroded / broken. Poor connections anywhere along the route will cause problems and most times intermittently, which are a real PITA to find. The TCCM could be bad as well. If I had to guess either your encoder motor is shot, or bad wires on the TCCM. 

If you're really into it, I'll post the schematics for the wiring of the system -- this will allow you to trace and test points along the system to pinpoint the problem. I hope I have given you some direction to be able to start troubleshooting your 4WD system. 

Here is a picture of your wire harness to your TCCM that you need to inspect for corrosion and damaged wires. http://kylestubbins.com/files/images/03_blazer_tccm_01d.jpg


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## tom99S104x4

melarosc said:


> I am seeing the same thing on my 2003 s10. All the LEDs on the dash switch are out. Just stopped working one day. I have verified the switch to be OK. The TCCM (transfer case control module) has all power and ground connections. I read that you can get diagnositic codes out of the TCCM by grounding pin 13 of the OBD connector under the stearing wheel. I did that and still the LEDs on the dash switch do not blink. I think this points to a bad TCCM, but I want some ensurance that this is the case before I lay out $400 for a new one. Anyone have any comments?


hi, on my 1999 S10 the tccm every once in a will stop working, but when mine acts up the lights on the dash switch will blink on and off when you try to get it in fwd hi or low. i took mine to the dealer the first time this happened and they replace the tccm at 500. cost to me. 300. for tccm and 200. labor. and they warranted it for one year. of coarse one year and a week later it did the same thing so i ordered a tccm online for 275. and pulled the kick plate off and removed the 3 nuts myself took all about 10 minuts and paid myself 225. labor for 10 minuts work. i was told the relays in the tccm go bad at the dealer, so i took the one i took out to see about checking out the relays in it but they are built into the circuit board and looks to difacult to mess with. after playing with it for awile i just for the hell of it put it back in and it worked fine again. i keep the spare tccm in my truck and when this problem happens i just swich them out and it works fine. there is a connector pluged into the tccm with a mess of wires on it and after a while i thought that it may be one of the wires are loose,but i played with them to see if it would get the fwd working and it won't,pulled the connector on and off the tccm and nothing, swich the tccms and bag it works. when your tccm is working you will here the relays click when you press the fwd button. hope this helps. tom


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## melarosc

Thanks for the info, but I did already have all the schematics. I did indeed have pin 13 on the diagnostic port grounded. I even made sure that I had a connection from this pin to the pin on the TCCM connector. When I did this, none of the LEDs on the switch blinked, no self test, no code. I know the switch is good because I ohmed it. I also verified the LEDs would light up by connecting their voltage and ground pins on the switch itself. This means the diagnostic circuit is not wroking at the TCCM....correct? If the diagnostic system isn't working , then it seems reasonable to think the TCCM is bad.


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## FanEAW

Take your time and start with the simple like always and check your 4WD selection button. Remove the switch panel from the dash, just pops out and test the wire leads to the switch. Did the TCCM Self test performed without any issues as noted.

( TCCM Self-Test: Observe the transfer case shift control switch indicators while turning the ignition switch to RUN. A properly operating system will flash all indicators and then will return to the current gear. If the system is operating normally, then proceed to Displaying Codes. )

Once again take your time and keep me posted, be glad to help you save some money and get your 4WD system working again soon.


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