4x4 not working

[BigBoomer]

4x4 not working(update now working)

Hello, I have read through all the 4x4 posts I could find and I don't see any that answers my problem. Let me start off with what was happening last winter. Oh BTW I have a 99 GMC suburban with the auto 4wd transfer case.

Last winter when I would put it in 4wd it was making a bad noise(almost like a wheel bearing roaring) but the 4wd was working then. The other strange thing that it was doing while in 4wd is when I would accelerate the steering was scary...I mean it was like only one front wheels was driving it. Not sure why I only had noise when it was in 4wd. I did replace the pitman arm since then so I don't know if that was part of the steering problem or not since I have not been able to get it in 4wd since replacing the arm.

Then in the spring one morning on the way to work the Service 4wd Light came on and then I could not get the 4wd to engage. I had no lights on the switch excect for at start up when all the lights will light up for a few seconds and then go out. So I started doing research and found the 4wd push button switch is a common problem. I found one out of a parts burban and swapped them and nothing. I can't even get the other switch I got to light up at start up. So randomly the indicator lights on the orignal switch would come on. One day I pulled in the driveway after work and the switch was lit up so I pushed the switch and I could hear the actuator on the front axle moving but it would not engage, the actuator would move but all that happened is the lights on the switch just blink.

Now for the past month I get nothing, the lights on the switch will not light up. When I push the switch I get no movement anywhere. I don't know what to try next. I don't know if the t-case switch is bad, or something in the front axle is not allowing it to engage or if the tccm is bad. Since the switch did work for a short time and I got movement at the actuator that really confused me.

I know this is a long post, sorry. I hope one of you could maybe point me in the right direction to go next. Thank you for reading this.

 

[SunlitComet]

I have not got all the tech data for the auto4's yet until maybe next month when I have some money but a few things:

0. Check the area that you were near for damage when it you did your pitman arm. And the fuses for the 4x4. #2 & #4 I think.

1. If your front acuator actually engages and stays that way the your t-case showed a complete shift internally.

2. If it tries to and then backs off your transfer case switch has gone bad or the cam inside that hits it.

3. It did not happen at all the switch could completely broken or the t-case has a problem.

4. If your light service light came on the tccm has either has an internal problem or your shift motor is having problems.

5. If your noise was there when you selector switch had a constant light that stayed that way and you had all four wheels active that would indicate a mechanical issuse. Could you specificy if the sound was at the front or under you?

6. If all your 4x4 fuses and wiring are intact with no lights at all your tccm would be the first thing to do. If you notice afterward that it shows a normal 2 hi but malfunctions in 4wd try the steps above. Any noise along the way pinpoint it and have that component inspected.

7. A blinking light on the function you selected would indicate the front axle actuator or sensor is not working but the transfer case has like ly completed his shift.

Start with that.

It sounds light shift motor malfunctioned and took out your tccm.

 

[BigBoomer]

Opps forgot to mention in my last post. I have checked all the fuses none are blown. The truck has never been in accident that I know of so there is no damage to the front axle. The truck has 190k on it, but the engine only has about 60k.

The noise it was making last winter sounded like it was coming from the front axle. It sounded like a wheel bearing or a rear end whine but I only heard while in 4wd. The sound was worse when I was on the gas. But looking back it may have been coming from the T-case. Since I would only hear it when the 4wd was engaged. I have checked all the fluid levels in the T-case and the front diff and they were fine.

After the Service 4wd light came on and when I could get the switch to work. I could push the 4hi button the actuator would move then pause for a second then move back out then lights would flash. Now I can't get the buttons to respond at all. That's what has me stumped. It seems like the switch is intermittent, but it also seems like there is another problem. The service 4wd light has been on and stayed on almost the whole time I've had this issue. There have been about 3 or 4 times it has went out and stayed out for about a day. Then it would come back on.

As of this moment now, the Service 4wd light is on. The lights only come on when I start the truck, then all four come on for a couple of seconds then go back out. The switch is not working at all.

Is there a way to test the TCCM or the dash switch? If I took it to a shop could they plug it in and read if there are any error codes stored in the tccm?
I can do any of the work to fix it myself I just don't have the scan tools to read trans codes or abs codes.

I know there are probably endless possibilities, I am just looking for a direction to go and check next. Sorry for the long post, I really do appreciate your help and response.

Thank you
Booomer

 

[SunlitComet]

There is a way to read them by blinking on mine anyway the switch light. What I have below to start with is for a 96 so verify thru a manual of yours if possible that the wire is the same on yours or take a chance. At least verify the color coding before trying with the pictue I included below. I have not purchased the service subsricption that gives full access to systems with auto 4wd. I do expect the procedures and codes will be the same with some extra stuff added.

http://www.sunlitcomet.com/images/automotive/62392543.gif

Displaying Diagnostic Trouble Codes

1. Install jumper wire between DLC terminal 13 and ground, Fig. 25 . The DLC is located under the lefthand side of the instrument panel, right of the steering column.
2. Turn ignition switch to On position.
3. Wait three seconds, then observe transfer case switch status lamps.

Reading Diagnostic Trouble Codes
The transfer case status lamps will flash to indicate the DTC's stored in memory. If only one DTC is stored in memory, that DTC flashes repeatedly with a three second delay between flash sequences. If more than one DTC is stored in memory, the first DTC flashes once, then the next code is flashed. This sequence continues to flash until the jumper wire is disconnected.

 

[BigBoomer]

Ok just got home from getting the codes read. They are co308 and co323. Not sure yet but I think it is pointing to the transfer case encoder motor. I am going to check the wiring harness that leads to the tcase motor first to make sure there are no broken wires. I'll keep you posted.

 

[bsamoul]

There is a way to read them by blinking on mine anyway the switch light. What I have below to start with is for a 96 so verify thru a manual of yours if possible that the wire is the same on yours or take a chance. At least verify the color coding before trying with the pictue I included below. I have not purchased the service subsricption that gives full access to systems with auto 4wd. I do expect the procedures and codes will be the same with some extra stuff added.

http://www.sunlitcomet.com/images/automotive/62392543.gif

Displaying Diagnostic Trouble Codes

1. Install jumper wire between DLC terminal 13 and ground, Fig. 25 . The DLC is located under the lefthand side of the instrument panel, right of the steering column.
2. Turn ignition switch to On position.
3. Wait three seconds, then observe transfer case switch status lamps.

Reading Diagnostic Trouble Codes
The transfer case status lamps will flash to indicate the DTC's stored in memory. If only one DTC is stored in memory, that DTC flashes repeatedly with a three second delay between flash sequences. If more than one DTC is stored in memory, the first DTC flashes once, then the next code is flashed. This sequence continues to flash until the jumper wire is disconnected.

I should have you take a look at mine since we're so close, because for the life of me can't figure it out

 

[SunlitComet]

Use this link and seperate text below to help you.

http://www.justanswer.com/uploads/MCVGreg/2008-02-15_210716_1998-Tahoe-C0323-Debug.pdf


C0308

NVG 236/246-NP8 Two-Speed Automatic



Circuit Description
The transfer case motor is a bidirectional, permanent magnet, D.C. motor. When energized, (through Motor Feed A or Motor Feed B. the ground is provided by the opposing Motor Feed circuit and then grounded through the transfer case shift control module ground circuit), the motor, through a series of gears, rotates the sector shaft which moves the mode and range forks to shift the transfer case between 4H, AUTO 4WD, 2H, N. and 4L ranges. While the transfer case motor is energized the transfer case shift control module also energizes the solenoid for the transfer case lock. The motor lock is disabled (locking action released) and free turning of the transfer case motor and sector shaft is then allowed.


This DTC detects a short to ground in Motor Feed A or Motor Feed B CKT.

Conditions for Setting the DTC

* The system will test the motor circuits:
* First, the system checks for unwanted voltage.
* Then, the system supplies voltage on one circuit and reads the voltage back on the other.
* If the system detects a problem with the circuits, the DTC is logged.
* The transfer case shift control module senses a low voltage return in Motor Feed A or Motor Feed B when a high voltage is expected.

Action Taken When the DTC Sets

* All shifting will be disabled.
* The SERVICE indicator (4WD/AWD) lamp will be latched on for the remainder of the current ignition cycle.

Conditions for Clearing the DTC

* The transfer case shift control module will clear the DTC if the condition for setting the DTC no longer exists.
* A history DTC will clear after 100 consecutive ignition cycles without a fault present.
* History DTCs can be cleared using a scan tool.




Test Description
The number(s) below refer to the step number(s) on the diagnostic table.
Listen for an audible motor noise when the encoder motor operates. Command both the ON and OFF states. Repeat the commands as necessary.

3. Tests for a short to ground in the Motor Feed A circuit.
4. Tests for a short to ground in the Motor Feed B circuit.
5. Tests for a higher than normal resistance in the Motor Feed A and B circuits through the module.
6. Tests for a short to ground in the encoder motor windings.
7. Tests for continuity across the motor circuit. Resistance readings vary depending on the location of the brush contact inside the motor assembly.
8. Tests Motor Feed A circuit for a short to ground.
9. Tests Motor Feed B circuit for a short to ground.
10. Tests Motor Feed A and B circuits for an open or high resistance.

 

[SunlitComet]

Hey Boomer, I got that data for 98-99 models I was was hoping for and you are actually on the right track go for you wires and motor. Let me know if you want more info on the system.

---------- Post added at 07:23 AM ---------- Previous post was at 07:22 AM ----------

Bsamoul, my offer still applies for documentation for you if you have a fax. You never responded to my last post in another thread about that.
I will have in the next two weeks the original 1996 4x4 system paper manual which should also cover a few more years accept auto 4wd but I should have a alldata subscription for that and applicable model year vehicle service manuals maybe thursday.

 

[BigBoomer]

Thanks sunlit, I really appreciate the help. I think I will try to go through it this weekend. Of course we are going to get snow on Sat so we'll see how it goes. Any other info you have on it would be great. Like I said Thank You very much for all the data and help you have given me so far.

Thank you
Boomer

 

[TeaDubya2011]

these are some long post..so if one of yall already said it, sorry..i'll bet it's the transfer case..mine was messed up, && it's gonna cost ya..ALOT