4d not working on 00 gmc yukon

[Soundguy]

wife needed to use 4wd tonight in her 2000 gmc yukon. it has the push buttons on the left of the dash.. auto, 2hi, 4 hi, 4 low.

nothing worked.. stayed in 2 hi... luckilly she managed to get unstuck without it.

when she got home I looked at it to mak sure it was a blonde moment or something. even read the manual as to operation to make sure there wasn't some arcane ritual of buttons to press while standing on yer head humming america the beautifull.. nope.. doing it right.. it's just not doing it right.

i looke dunder the hood at the fuse box.. didn't see one for the electric xfercase.. and nothing looked burned.. no relay's were id's as having anything to do with drivetrain other than ABS.

I scanned the truck for codes, no set codes, no pending codes, and the CE lamp wasn't on anyway.. so it was a stretch.. for the test.. etc..

any clues?

we don't use 4wd often.. but I have used it within the last 2 ys. and when i have used it in the past, it blinks and then goes into the selected gear.. or if using auto, that comes on.. and when shifting between, i recall heairng a motor running or some other electric oriented sound.. solenoid or servo shifting.. something. but not now.. it's like you are not even pushing the buttons.

can't even do the arcane shift transfer case to neutral by turning on key, setting parking brake, adn then pressing 2hi and 4 lo for 4 seconds to put xfer case into bneutral for towing. won't even do that.

i have had the xfer case and front diffy serviced before, and have done it myself ( oh so much fun.. )

manual is real helpfull.

tells you about the 4 buttons, adn then said if it doesn't work, take it to the dealer.

any guidance here?

thanks

soundguy

 

[lilranch2001]

wife needed to use 4wd tonight in her 2000 gmc yukon. it has the push buttons on the left of the dash.. auto, 2hi, 4 hi, 4 low.

nothing worked.. stayed in 2 hi... luckilly she managed to get unstuck without it.

when she got home I looked at it to mak sure it was a blonde moment or something. even read the manual as to operation to make sure there wasn't some arcane ritual of buttons to press while standing on yer head humming america the beautifull.. nope.. doing it right.. it's just not doing it right.

i looke dunder the hood at the fuse box.. didn't see one for the electric xfercase.. and nothing looked burned.. no relay's were id's as having anything to do with drivetrain other than ABS.

I scanned the truck for codes, no set codes, no pending codes, and the CE lamp wasn't on anyway.. so it was a stretch.. for the test.. etc..

any clues?

we don't use 4wd often.. but I have used it within the last 2 ys. and when i have used it in the past, it blinks and then goes into the selected gear.. or if using auto, that comes on.. and when shifting between, i recall heairng a motor running or some other electric oriented sound.. solenoid or servo shifting.. something. but not now.. it's like you are not even pushing the buttons.

can't even do the arcane shift transfer case to neutral by turning on key, setting parking brake, adn then pressing 2hi and 4 lo for 4 seconds to put xfer case into bneutral for towing. won't even do that.

i have had the xfer case and front diffy serviced before, and have done it myself ( oh so much fun.. )

manual is real helpfull.

tells you about the 4 buttons, adn then said if it doesn't work, take it to the dealer.

any guidance here?

thanks

soundguy

I had problems with my 2003 Silverado, dealer went through a whole list of parts, never did resolve it, so I went to the front door, walked in and traded it.
They asked me if I had any problems with it, I stated I just had the tranny serviced, they said ok, and we made the deal

 

[SSdoxie]

Getting power to the switch? Without power there the indicator light(s) won't work and the computer can tell when you are trying to shift so won't register a code.

 

[Soundguy]

green lamp for 2hi is on like normal, and at startup all lamps work for gear selections and neutral.

so.. yeah.. it's getting power.

soundguy

 

[JD230511]

Just a shot in the dark. Could it be a vacuum line??

 

[Soundguy]

i don't believe that is a vacume system, but rather a servo or solenoid engaged from the transfer case. and if it was a vac line.. I think it might TRY to shift, and blink the lmaps as if it was doing so. manual does mention that if it tries to shift, and can't, it will try to go back to the previous gear selection that worked. and any time trying to shift.. the coresponding lamps blink.

since no lamps try to blink.. I don't even think it is trying to shift.

wonder if it has some sort of smurf oil sensor in there or something..

soundguy

 

[Damifino]

Soundguy,

Had a similar proplem a few years back, I discovered a actuator that screws into the left side of front axle, I believe it was around 50 some dollars.

It has an electric plug in terminal on the end that heats the gas inside and pushes ram to engage.

Look up 4 wheel drive actuator and look for replacement for your model, it will at least let you know what to look for underneath, could be the wire was snagged off or broke or defective actuator.

Good Luck

 

[Zebrafive]

Does it have a "service 4wd" light? Is it ON?
Did you check instrument panel fuses? #2 T CASE, #24 4WD?
Look underneath for any wiring unplugged, snagged, broken.

 

[Cpjlube]

There is a transfer case control module (tccm) on those trucks, I believe. You can run a diagnostic on it to check some of its operation. Might be worth a shot before taking it in to the shop.

I have done it before with some success. But can't say it solved all my issues.

This is the best description I could find.


You don't need a reader to get the tccm code. TCCM codes are, 1, 2, 3, 4

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.

 

[automech]

You can try a light tap on the encoder motor at the transfer case while a helper is using the buttons to engage 4hi and 2hi. The encoder is the most common failure point on these. They tend to rust/stick into 2 hi if they are never used. If the hammer /light tap fails, go for the code next. If it moves after hitting it you know where the problem is. Normally I go straight for the codes, but my scanner will access and command the transfer. If I was out in the boonies, and needed 4 whl, I would go straight to the hammer.