Two Speed Rear Axle Inoperative Air-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. This circuit will only affect speedometer operation, which assumes the two speed rear axle system is operating normal (mechanically). When the rear axle switches from LOW to HIGH, for example, the two-speed rear axle air shift switch opens, removing the voltage at the speedo adapter (LP4/L21/early LG5) or from the powertrain control module (late LG5). The speedometer then changes the calibration so that the speedometer reading matches road speed. When the two-speed rear axle shift control valve is placed back in the LOW position, the shift system's air supply is closed off. The loss of air pressure closes the two-speed rear axle air shift switch, allowing current to flow to the speedo adapter (early LG5) or powertrain control module (late LG5). Applying voltage to the speedo adapter/powertrain control module changes the speedo calibration to match the low gear.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This step tests for proper ignition 3 voltage at the two-speed rear axle air shift switch.
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This step tests for proper operation of the two-speed rear axle air shift switch.
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This step tests for proper operation of the two-speed rear axle air shift switch.
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This step tests the air shift switch signal circuit for an open or high resistance.
Step | Action | Value(s) | Yes | No |
Schematic Reference: Two-Speed Rear Axle Schematics | ||||
1 | Did you review the Two-Speed Rear Axle Shift Description and Operation and perform the necessary inspections? | -- | Go to Step 2 | |
2 | Verify the fault is present. Does the system operate normally? | -- | Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems | Go to Step 3 |
Does the voltage measure within the specified value? | 9-14 V | Go to Step 4 | Go to Step 6 | |
Is continuity present across the switch? | -- | Go to Step 5 | Go to Step 8 | |
Is continuity present across the switch? | -- | Go to Step 8 | Go to Step 7 | |
6 | Repair the an open or high resistance in the ignition 3 voltage circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 9 | -- |
Repair the open, high resistance, or short to ground in the air shift switch signal circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 9 | Go to Speedometer and/or Odometer Inaccurate or Inoperative in Instrument Panel, Gages, and Console | |
8 | Replace the two-speed rear axle air shift switch. Refer to Two Speed Rear Axle Shift Control Switch Replacement . Did you complete the replacement? | -- | Go to Step 9 | -- |
9 | Operate the vehicle within the conditions for causing the symptom as specified in the supporting text. Does the symptom re-occur? | -- | Go to Step 2 | System OK |
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 or the powertrain control module. 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 speedometer 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.
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This step tests for proper ignition 3 voltage at the two-speed rear axle shift relay.
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This step checks the shift motor relay control circuit and the two-speed rear axle driver control switch for a short to ground.
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This step tests the shift motor relay control circuit and the two-speed rear axle driver control switch for an open.
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This step tests the high gear shift motor control circuit and the shift relay for proper operation.
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This step tests the low gear shift motor control circuit and the shift relay for proper operation.
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This step tests for a proper ground circuit.
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This step tests the shift motor relay control circuit for a short to ground.
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This step tests the shift motor relay control circuit for an open.
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This step tests the rear axle shift relay.
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This step tests the rear axle shift relay.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Schematic Reference: Two-Speed Rear Axle Schematics | ||||
1 | Did you review the Two-Speed Rear Axle Shift Description and Operation and perform the necessary inspections? | -- | Go to Step 2 | |
2 | Verify the fault is present. Does the system operate normally? | -- | Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems | Go to Step 3 |
Does the voltage measure within the specified value? | 9-14 V | Go to Step 4 | Go to Step 13 | |
Does the test lamp illuminate? | -- | Go to Step 9 | Go to Step 5 | |
Set the two-speed rear axle driver control switch to the HIGH position. Does the test lamp illuminate? | -- | Go to Step 6 | Go to Step 10 | |
Does the voltage measure within the specified value? | 9-14 V | Go to Step 7 | Go to Step 11 | |
Does the voltage measure within the specified value? | 9-14 V | Go to Step 8 | Go to Step 12 | |
Connect a test lamp from the low gear shift motor control circuit to the ground circuit on the shift motor connector Does the test lamp illuminate? | -- | Go to Step 14 | Go to Step 15 | |
Does the test lamp illuminate? | -- | Go to Step 16 | Go to Step 17 | |
Does the test lamp illuminate? | -- | Go to Step 17 | Go to Step 18 | |
Does the voltage measure within the specified value? | 9-14 V | Go to Step 19 | Go to Step 20 | |
Does the voltage measure within the specified value? | 9-14 V | Go to Step 19 | Go to Step 21 | |
13 | Repair the open or short to ground in the ignition 3 voltage circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 22 | -- |
14 | Replace the two-speed rear axle shift motor. Refer to Two Speed Rear Axle Shift Motor Replacement . Did you complete the replacement? | -- | Go to Step 22 | -- |
15 | Repair the open in the ground circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 22 | -- |
16 | Repair the short to ground in the shift motor relay control circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 22 | -- |
17 | Replace the two-speed rear axle driver control switch. Refer to Two Speed Rear Axle Shift Control Switch Replacement . Did you complete the replacement? | -- | Go to Step 22 | -- |
18 | Repair the open in the shift motor relay control circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 22 | -- |
19 | Replace the two-speed rear axle shift relay. Refer to Two Speed Rear Axle Shift Motor Relay Replacement . Did you complete the replacement? | -- | Go to Step 22 | -- |
20 | Repair the open in the high gear shift motor control circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 22 | -- |
21 | Repair the open in the low gear shift motor control circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 22 | -- |
22 | Operate the vehicle within the conditions for causing the symptom as specified in the supporting text. Does the symptom re-occur? | -- | Go to Step 2 | System OK |
