Two Speed Rear Axle Inoperative (Electric-Operated)

Two Speed Rear Axle Inoperative (Electric-Operated)

Circuit Description

This symptom is usually the result of actions that were expected to take place during the transition between rear axle gears and have not occurred. When the two-speed rear axle driver control switch is in the LOW position, the two speed rear axle shift relay is de-energized and ignition 3 voltage is supplied to the speedo adapter (L18/early LG5) or the powertrain control module (late LG5). With ignition 3 voltage supplied to the speedo adapter/powertrain control module, speedometer calibration is set for low gear.

When the two speed rear axle driver control switch is placed in the HIGH position, the switch closes to ground removing ignition 3 voltage from the speedo adapter/powertrain control module and energizes the two speed rear axle shift relay. Voltage is supplied to the two speed rear axle shift motor from the two speed rear axle shift relay and shifts to high gear. The speedo adapter/powertrain control module then changes the calibration so that the speedometer reading matches road speed.

Test Description

The numbers below refer to the step numbers on the diagnostic table.
3. This step tests for proper ignition 3 voltage at the two speed rear axle shift relay.
4. This step checks the shift motor relay control circuit and the two speed rear axle driver control switch for a short to ground.
5. This step tests the shift motor relay control circuit and the two speed rear axle driver control switch for an open.
6. This step tests the high gear shift motor control circuit and the shift relay for proper operation.
7. This step tests the low gear shift motor control circuit and the shift relay for proper operation.
8. This step tests for a proper ground circuit.
9. This step tests the shift motor relay control circuit for a short to ground.
10. This step tests the shift motor relay control circuit for an open.
11. This step tests the rear axle shift relay.
12. This step tests the rear axle shift relay.