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GMC Forum: Four Wheel Drive Not Working
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  #1  
Old 08-08-2010, 03:51 PM
NITWIT NITWIT is offline
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Default Four Wheel Drive Not Working

When I push any of the buttons on the dash nothin happens. The 2 HI light is on as usual. When the iginition is first turned on they all light up for a sec. like they always did.
I pulled the button cluster out and resoldered the connections at the plugs thinking that maybe their was a bad connection.
Fuse is ok under the hood. Can anyone point me in the right direction?
Thanks.
2000 Sierra 2500
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Old 08-09-2010, 08:20 AM
Molson02536 Molson02536 is offline
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Quote:
Originally Posted by NITWIT View Post
When I push any of the buttons on the dash nothin happens. The 2 HI light is on as usual. When the iginition is first turned on they all light up for a sec. like they always did.
I pulled the button cluster out and resoldered the connections at the plugs thinking that maybe their was a bad connection.
Fuse is ok under the hood. Can anyone point me in the right direction?
Thanks.
2000 Sierra 2500
Have your Sierra scanned for a DTC code that may indicate where the issue may need to be addressed.

There are 2 types of shifts - mode shifts, and range shifts. A mode shift would be from 2HI to 4HI, and vise versa. A range shift would be in and out of 4LO. You can Mode shift any time when moving, but must be stopped in neutral to do a range shift.

Normal Operation: When the switch is pressed, the indicator light flashes, and the TCCM tells the encoder motor to move from its current position to the desired position. When the transfer case enters 4HI, it engages the vacuum switch to engage the front axle. The axle switch then tells the TCCM that it's engaged. Then the 4wd indicator light will come on. The transfer case has 3 positions. 2HI, 4HI, and 4LO, in that order. T he encoder motor senses which position it is in, and tells the TCCM definitively where the transfer case is.

Common problems:
Switch failure: Nothing works. Pushing either end causes NOTHING to actuate (No sound from dash or transfer case)

Encoder failure: Transfer case will not enter 4HI, but will enter 4LO. This is because the computer doesn't know exactly what position the case is in, so it just moves to either extreme (2HI or 4LO).

Actuator failure: The transfer case changes position, but the front axle never engages. Takes an extended time for the indicator lights to come on.

Secondary problem list:

4wd does not engage:
Front axle actuator wire harness is damaged
Faulty front axle actuator bad
Faulty transfer case switch
Faulty 4wd indicator lamp
Blown TCCM fuse
Bad electrical connections
Faulty switch
Faulty encoder motor
Faulty TCCM Faulty transfer case
Faulty front axle

4wd will not disengage:
Faulty wiring
Faulty lamp
Transfer case switch faulty
Actuator bad
Faulty switch
Faulty encoder motor
Faulty TCCM
Faulty front axle


For OBD-II vehicles with push button between the instrument panel and the radio/HVAC control stack:


The diagnostic trouble codes are displayed on the three transfer case shift select buttons located on the instrument panel. When the connector pin 13 on the data link cable is grounded to pin 4, and the ignition switch has been OFF for at least five seconds prior to positioning the ignition switch to run the shift select buttons will blink various times together in order to indicate a diagnostic trouble code from 1 to 4. http://www.2carpros.com/forum/automo...alic_DLC_1.jpg

Position the ignition switch to OFF. Ensure the ignition switch is positioned to OFF for at least 6 seconds. Connect pin 13 on the data link cable to a vehicle ground source. The data link connector is located in the cab under the instrument panel on the driver's side. Position the ignition switch to RUN. Note the shift select buttons for blinking codes.
If the shift select buttons all blink one time and stop, and do not continue to blink, no fault codes are stored in the TCCM. The transfer case shift select buttons will blink in order to identify any stored trouble code. If only one code is stored in the TCCM memory, that code will blink repeatedly with a three second delay between blinking sequences. If more than one code is stored, the first code will blink once, then after a three seconds delay, the next code will blink. This sequence will continue until pin 13 is no longer grounded.

When reading the diagnostic trouble codes, the number of shift select buttons blinks will indicate the code number.


The error codes are:
1 - When the ignition switch is positioned to RUN the TCCM test to determine if RAM standby Power (maintained battery power) to the TCCM was lost since the ignition was last turned OFF. When power is interrupted on pin C6 of the TCCM, the TCCM stores a loss of RAM standby power.

2 - During electronic shifting, the TCCM check the motor/encoder for normal operation. If the motor/encoder does not function correctly enough times, the TCCM stores a motor/encoder failure DTC 2.

3 - The TCCM performs a test each time the electronic-shift motor is turned ON or OFF. If the motor does not function properly the TCCM stores a motor circuit failure DTC 3, and the shift select buttons blink in order to inform the driver of a problem.

4 - Each time the ignition is turned ON, the TCCM tests the memory, the program, and the internal system in order to ensure that the TCCM is operating properly. If the TCCM detects a fault within the TCCM, the TCCM stores a RAM/ROM memory failure (DTC) 4.


How to fix common push button 4wd problems:

If you have codes 2 or 3 check all the encoder motor connections at the transfer case, if those check out OK, you will probably need a new encoder motor.
If you have code 4, replace the TCCM.

Make sure all connections are good and no corrosion, and then it's either an encoder or TCCM.
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Old 08-09-2010, 09:24 AM
NITWIT NITWIT is offline
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I scanned earlier for DTC codes and there was none. (I have the Auto Tap software installed on a computer here in my garage.)
I don't see a TCCM fuse but I do have a fuse labeled ATC which is good. I'll go underneath and the connections at the axle and transfercase and post back.
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Old 08-09-2010, 10:23 AM
NITWIT NITWIT is offline
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All the connections look good. I think I'll go ahead and order the push buttons. $34.00 plus shipping.
[IMG]<a href="http://s28.photobucket.com/albums/c201/camaro396/Other/?action=view&current=1ba05680.jpg" target="_blank"><img src="http://i28.photobucket.com/albums/c201/camaro396/Other/1ba05680.jpg" border="0" alt="Photobucket"></a>[/IMG]
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Old 08-09-2010, 10:27 AM
NITWIT NITWIT is offline
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Connections look good. I think I'll order the button switches. 34.00 plus shipping.


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  #6  
Old 08-09-2010, 10:28 AM
NITWIT NITWIT is offline
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Connections look good. I'll order new switches and try that.

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Old 08-09-2010, 10:39 AM
NITWIT NITWIT is offline
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Connections look ok. I think I'll order new button switches and try that.
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