Electronic Rear Differential Lock Will Not Engage

Electronic Rear Differential Lock Will Not Engage

Circuit Description

The rear differential control circuit consists of an actuator which engages and disengages the rear axle differential lock. The rear differential actuator consists of a coil assembly, and a locking assembly with springs and pins to lock the rear differential, all within the rear differential assembly.

The rear axle differential lock actuator consists of the following circuits:

* The rear differential lock control circuit, which is connected to the transfer case shift control module and supplies battery voltage.
* The rear differential lock return ground circuit, which is also connected to the transfer case shift control module.

Whenever the rear differential lock has been requested the transfer case shift control module provides battery voltage through the rear differential lock control circuit, and provides ground through the rear differential lock return circuit through a current limiting driver.

Whenever a rear differential lock is requested the transfer case must be in 4LO and the vehicle speed must be below 5 km/h (3 mph) for the request to be accepted. The rear differential lock will remain locked up to 32 km/h (20 mph) after which the rear differential lock will disengage.

Test Description

The numbers below refer to the step numbers on the diagnostic table.
2. This step determines if the fault is present or intermittent.
3. This step determines if the transfer case shift control module is receiving a differential lock request from the transfer case shift control switch.
4. This step determines if a bad switch is causing the symptom.
5. This step determines if a short, open, or high resistance in the 5-volt reference or switch signal circuits is causing the symptom.
6. This step determines of the coil has excessive resistance or if the windings are shorted together.
7. This step determines if the coil or pigtail is shorted to ground.
8. This step determines if either the differential lock control or differential lock return circuits are shorted to ground.
9. This step tests for an open or high resistance in both the return and control circuits.
10. This step refers to transfer case shift control module replacement.
11. This step refers to encoder motor replacement.
12. This step replaces the transfer case shift control switch.

Step 1 - Step 10:

Step 11 - Step 13: