Hello,
I'm new to the world for pick-up trucks and 4x4's and I just bought a 1997 Sierra 1500 which is currently locked in 4x4 at all times. It is an automatic and I was wondering what the problem most likely is, how can I more precisely diagnose it and how do I fix it ?
Thanks,
Greg McCool
On the full size, the front actuator is electric, not vacuum.
When in 4wd mode, a switch on top of the transfer case conducts 12 volts out to the actuator. Wire #50 (brown) is the 12v feed, and it conducts to the light blue wire (#900) to the actuator.
When shifted out of 4wd, the switch opens up and no voltage goes to the actuator.
I'll assume it is the actuator, if the plug to the actuator is getting 12 volts when in 4wd. The way this actuator works, is it is a sealed chamber that gets heated by voltage. When it heats, the pin in the end swells and pushes a shift fork in the front differential. The shift fork engages a spline on the passenger side of the differential, and boom! you have 4WD.
GM offered an upgrade to this actuator that is a motor instead of a heated device. However, it requires a small harness addition, a spacer, and a new actuator. It is about a $150 to $200 option.
Good luck. The actuator is usually the problem 90% of time but recheck all of the wire harness just to maker sure there is no short before replacing any parts. The actuator may not be fully engaged or disengaged and the fork to the spline may be what is causing the whining or grinding noise you hear.
88-UP C/K ACTUATOR UPGRADE
VEHICLE SERVICED: GM/
CHEVROLET FULL SIZE
PURPOSE: IMPROVE AXLE CONNECT ENGAGEMENT TIME AND
COMPONENT RELIABILITY.
SYMPTOMS: NO FRONT DRIVE AXLE ENGAGEMENT WHEN SHIFTED INTO 4X4.
Obtain the following GM part numbers:
(1) 26060073 Actuator
(1) 88959465 Harness/Spacer Kit
On the passenger side of the front axle the actuator is screwed in, if it's still the old thermal actuator it is metal with a 2 wire plug, the newer ones are plastic and have three wires(production started in 98) and the axle engages immediately.
First look at the passenger side of the front axle about even with the extension(part the CV axle bolts to on pass. side), if its metal with a 2 wire plug its part number 26013495(thermal actuator). If its a plastic unit extending 5 inches or so out of the axle with 3 wires, you have the newer style actuator- stays locked in with key off, don't have to wait more than 2 seconds for axle to lock in- part number 26060073. If you want to upgrade to the new style and your vehicle GVW is not over 8500 lbs you will need part number 26060073 and a adapter wiring harness # 88959465 Harness/Spacer Kit.
Good luck and keep us posted.
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, 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.
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 drivers 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.
How to replace the TCCM
The TCCM is located behind the glove box, and is accessed from underneath the dash. In order to get to it, the kick panel and black cover need to be removed. Then a 1/4" screw holds the TCCM and ECM in the dash. The middle computer is the ECM, the one on the backside is the TCCM, and on the front is the small ABS computer. Simply loosen the two 10mm nuts on each side, and they will separate.
How to fix the encoder motor
Cheap way - To clear the codes and reset the computer, pull the 5 amp TCCM fuse, located at the bottom of the fuse box. Wait at least a half hour, and then replace the fuse. Turn the ignition key to run, wait for the 4x4 lights to blink, and then turn off. Repeat 5 times, and then start the truck.
Reasonably priced way -
http://www.northernautoparts.com. The part costs around $140 with a 1 year warranty and $38 core refund when you send the old one back.
Expensive way - buy a brand new one from GM for over $300.
How to install the encoder motor
Lucky way - The only thing that needs to be removed is the encoder motor itself. Tools needed are a 10mm hand wrench and an 8mm and 10mm socket wrench. The 10mm socket will work on the upper and lower bolts, while the regular wrench is needed for the middle bolt. (Tight squeeze!). The 8mm socket is for the electric plug. Remove the bolts and connector, then, just pull and wiggle it out of the truck. Install in reverse order.
Unlucky way - This means the encoder motor did not just wiggle out. Now the front drive shaft will have to be removed at the transfer case. Then, a yolk puller is needed in order to remove the yolk from the transfer case. Once this is done, go back to the directions in lucky way.
