05 TB EXT - Service 4WD light on - No 4WD

[Trale Blayzen]

My "Service 4WD" light is on and I am unable to switch out of 2WD. When I select another mode, the 2WD LED remains lit while the un-attainable 4WD mode LED just flashes.

I recently bought a Innova 5510 scanner but it does not detect any TCCM, so trouble-shooting is a challenge. I would like to at least visually inspect the TCCM connectors.

My research has turned up some sources that say the TCCM is below the driver's side dash, but I do not see one. Other sources say the 2005 TB doesn't have a separate module, and TCCM is integrated into the PCM or TCM?

I have downloaded and read the related great tech docs on this site. 2005 model year diagrams are not there, but the '04 and '06 docs are very useful. Thank You Mooseman!

So my questions are:
Does a 2005 TB EXT have a separate TCCM? If so, where is it located?
Do you know if the Innova 5510 is able to query the TCCM? (it's sold as an "all systems scanner).

Possibly useful/related background info. The "service 4WD" light came on within a few minutes of the "Check Engine" light on a short 5 mile drive. I was not trying to change out of 2WD. 4WD has only been used occasionally in the winter during the past 15 years.

The check engine error code pointed to an open circuit on the Intake Air Temp sensor. I fixed this but I'm suspicious of an electrical problem with TCCM also.

adTHANKSvance for any insight.

 

[Mike534x]

If I recall correctly, those Innova scanners are more general purpose while providing a bit more detailed information. You'd need a more advanced scanner like the Autel MK808BT, Snap On Solus or a GM Tech 2 to really be able to access the PCM/TCM/TCCM on these trucks.

The TCCM is inside the driver side of the dash. When you open the door, there's a panel (as seen in the picture) with 4 connectors attached to it. Are you sure the TCCM is the issue?

A few things it could be;

1. TCCM
2. 4WD Selector Switch (they get flakey, sometimes turning the knob back and forth several times between each mode with the truck off will clear off any build up on the contacts. The switch itself is cheap at about 15 bucks on Amazon)
3. Transfer Case Encoder Motor
4. Faulty Encoder Motor Sensor
5. Wiring issue between the switch, TCCM or Encoder Motor

 

[Mooseman]

Another option for a scanner is a Bluetooth ELM327 and the Car Gauge Pro app on Android. That app can scan for all codes on all systems.

All GMT360/370 (SWB/LWB) have a separate TCCM and located as @Mike534x explained.

Another thing to check is the fuses.

The fact that the 4HI light flashes tells me that the TCCM is alive and trying to do something. If it was the TCCM itself, it would flash all the lights and then all go out. When you switch to 4hi, does first flash and then turn on the service 4x4 light? Or does it come on as soon as you turn on the ignition?

My shot in the dark guess would be a bad encoder motor, either the motor or its sensor.

 

[Chickenhawk]

Good advice from Mike and Moose. Starting with the easiest (and cheapest) solution, exercise the switch about 50 times with the vehicle off.

The TCCM is the least likely problem on an 05. Most likely is the encoder motor, especially if 4WD is used rarely.

Next on the list is wiring between the encoder motor and TCCM.

My money is on the encoder motor. But you can sometimes diagnose by sound. With the ignition on but the vehicle, fan, radio etc. all OFF, cycle through each setting on the switch and report back what you hear. If working properly, 2WD to A4WD should have two sounds; one is the disconnect and one is the encoder motor. A4WD to 4WD should only have one sound from the encoder.

 

[Trale Blayzen]

Thank you guys! I found a panel on the left side of the dash. (did not see a picture in your post) Underneath the panel was the module shown in the pic. Transfer Case Shift Control Module?

I am not sure the TCCM is the issue. It could be any of the things you listed except I think the selector switch is OK. It "acknowledges" a change in selection as it always used to by flashing the selected mode LED. Except now it just flashes continuously and doesn't change mode. When I set it back to 2WD, all is good (except the 4WD light on instrument cluster). The Service 4WD has stayed on continuously since it first came on.

My code reader is able to detect and query ECM, TCM and BCM (+many other systems) on my '04 Dodge and '12 Honda. on my TB, it detects/queries the PCM, BCM, both door and liftgate modules + other stuff but no TCM is shown. That seems odd.

I will try the sound test tomorrow. Thanks again.

 

[Trale Blayzen]

I did some more digging but no pay dirt yet.

I checked the fuses:
Rear under-seat fuse block [#35 TCM] and [#48 Four-Wheel Drive]
Engine compartment fuse block [#8 Automatic Transfer Case]
All good.

Sound diagnosis:
-When switching from 2WD to A4WD, short "bzzzzt" sound. Less than 1 second long. A4WD light flashes continuously, 2WD remains on solid
-When switch from A4WD to 4WD, similar sound. 4WD drive LED flashes continuously, 2WD LED solid on.
-Switching back, slightly different sounds, same duration.
-When going from A4WD to 2WD sound ends with a "hard stop"
This sounds like a stepper motor in action?
The 2WD to A4WD transition sound did not seem to have two distinct sounds.

Is the picture in my previous post the TCCM? I'm assuming the long narrow connector laying loose is ok?

Sounds like next stop is the Encoder Motor.

Thanks again.

 

[Mike534x]

Yeah the module in your picture is the TCCM. The connectors/wiring look to be in order, it doesn't look loose? Sounds like a possibly bad encoder motor.

This is an older "How-to" for diagnosing a non-functioning 4WD posted here a while ago.

4WD not working? Step inside.

There seems to be quite a lot of mystery to newer folks when their 4x4 functions stop working. Since crappy weather season is upon us a lot of people are trying their 4WD functions for the first time this year... and discovering all isn't as it should be. Here's my attempt at a troubleshooting...

gmtnation.com

 

[Mooseman]

Is the picture in my previous post the TCCM? I'm assuming the long narrow connector laying loose is ok?

That long black single row connector is the data bus connector with its "comb" inside. It's basically where all modules connect and used for diagnosing issues with the network and modules.

 

[Trale Blayzen]

Thanks again guys. Great info!

This is an older "How-to" for diagnosing a non-functioning 4WD posted here a while ago.

4WD not working? Step inside.

There seems to be quite a lot of mystery to newer folks when their 4x4 functions stop working. Since crappy weather season is upon us a lot of people are trying their 4WD functions for the first time this year... and discovering all isn't as it should be. Here's my attempt at a troubleshooting...

gmtnation.com

I read the whole post and linked pages and learned a ton about this part of my truck. Very useful

That long black single row connector is the data bus connector with its "comb" inside. It's basically where all modules connect and used for diagnosing issues with the network and modules.

Also very informative. I'm new to GMs network implementation, and much more here. I'm guessing that the module I found under the dash near the steering wheel is the "data communications module". It looks like it has (at least) 2 of these data bus connectors (populated).

I did the sound test again with an assistant to operate the 2WD/A4WD switch. I don't know what a working unit sounds like, but it sounds like the encoder/motor is working. I do not hear a click from the front axle disconnect, even with my mechanic's stethoscope on the actuator. Connector/wires look OK externally, but I'll remove and inspect. Can this thing be checked with a multi-meter?

<speculation mode on>
I removed the front tire for better access and the wheel turns freely, so is safe to assume the actuator is stuck in the "disconnected" mode and it's OK to drive the vehicle until this is fixed?

 

[Mike534x]

Just by chance, would you be able to record the sounds it's making when switching from 2WD, A4WD and 4Hi and then back to 2WD? Might help with giving us all an idea if it sounds like a working unit.

 

[Trale Blayzen]

Just by chance, would you be able to record the sounds it's making when switching from 2WD, A4WD and 4Hi and then back to 2WD? Might help with giving us all an idea if it sounds like a working unit.

I can do that.

All of the actuator wires and connector pins look good. I "worked" them to burnish contacts.
I removed the actuator and with it connected to the vehicle, it does nothing when changing 4WD modes. Cannot find a pin-out for the connector but looks like it's a motor with feedback sensor. The grease on it and inside the hole looks good.

Head-scratcher: While I was putting it all back together I ran across a broken wire. It appears to be light green with no stripe. It has its own black plastic tube breaking out near the actuator wiring tube.

 

[Trale Blayzen]

I recorded it but site will not permit upload .mp3 file.

 

[flyboy2610]

Head-scratcher: While I was putting it all back together I ran across a broken wire. It appears to be light green with no stripe. It has its own black plastic tube breaking out near the actuator wiring tube.

Fix it and see what happens. That might the issue.

 

[Mooseman]

I recorded it but site will not permit upload .mp3 file.

You have to upload it to a third party site, like YouTube or SndUp and post the link to it.

That wire sounds like it could be the problem but I don't see a green wire to the disconnect actuator. The only other wires around there I can think of are for the oil pressure switch however neither of those are green.

You could also check for the voltages according to the schematics attached but I'd bet that the actuator is borked. With the actuator out, use a screwdrive or something to push on the plunger inside the disconnect to see that it moves freely. It is spring loaded.

 

[Trale Blayzen]

As luck would have it, not too long after ordering a new actuator, I found the problem. It is a broken wire. My LED flashlight makes it look green. It looks a little more yellow in the picture as displayed on my computer monitor. No matter. GM must have switched from blue to yellowish-green on this wire. There's some other damage to a yellow/green twisted pair in the same conduit where the actuator wires break out. They are not severed, but the whole mess looks like it got caught in a grease monkey's oil filter tool to me. All of the conduits were clamped to the frame properly.

edited to ask: Does anyone know what the yellow/green twisted pair go to? They take a turn toward to top of the frame/engine.

 

[Mooseman]

Maybe the oil pressure switch? It's right above the oil filter.

 

[Trale Blayzen]

I tried to follow the conduit and it looks like one end goes to the right side of the frame and connects to a vacuum switch/sensor. What appears to be the vacuum line follows the suspension upper wishbone.
I have not been able to verify using the wiring diagrams.
Thanks!

 

[Mooseman]

Maybe the ABS wheel speed sensor?

 

[TollKeeper]

Let me ask a simple, but commonly overlooked, cause of the issues you described.

Whens the last time you opened up the fill port on the transfer case, and checked the fluid level?

If its low, or extremely low, the gearing could be dry, and not allowing the "slip" of the gears the needs to happen when engaging the system.

Also, when is the last time you changed your diff fluid. The GM transfer cases are VERY picky about fluid service intervals.

The transfer case takes, what is referred to around here as, Smurf Blood. Also known as Auto-Trak II fluid. Can be found at Advance Auto, NAPA, and Amazon. Just as the name indicates, its a VERY Blue fluid. And if its not BLUE, its way past its service interval, or if its red, someone put in the wrong fluid (very common occurrence).

If a service is required/needed. After performing the service, take it out for a good 25 mileish drive, to try to get that fluid worked back into the gears, gear faces, and bearings, and then try to select the 4WD, not A4WD, operation. @Mooseman has said previously its best to try full operation the system, rather than half operation, when trying to diagnose the 4x4 system.

You should hear a operation at the front passenger side of the vehicle, the inter-axle disconnect. With that corner jacked up, after hearing it engage, you should be able to turn that wheel, and either the wheel on the opposite side, or the drive shaft to the differential, should turn. If it doesnt, you have at least found the 1st of your problems