Two Speed Rear Axle Inoperative Air Operated
Circuit Description
This symptom is usually the result of actions that are expected to take place during the transition between rear axle gears that have not occurred. This circuit only affects speedometer operation, which assumes the two-speed rear axle system is operating normally. 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 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 ignition 3 voltage circuit for an open or high resistance.
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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 System 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 | |
Test for 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 the symptom to occur as specified in the supporting text. Does the symptom occur? | -- | Go to Step 2 | System OK |
Two Speed Rear Axle Inoperative Electric Operated
Circuit Description
This symptom table aids in diagnosing a failed two-speed rear axle shift attempt. When the ignition switch is in the RUN position, the voltage is present on the ignition 3 voltage circuit at the two-speed rear axle relay. The two-speed rear axle switch provides a ground path for the coil in the relay. When the switch is in LOW range, the relay is de-energized and voltage is present on the shift signal circuit at the two-speed rear axle motor. When HI range is requested, the switch closes and the relay energizes. Voltage is no longer present on shift signal circuit at the motor, but is present on the shift motor control high gear circuit at the motor. When voltage is present on the shift motor control high gear circuit, the motor completes the shift and brake automatically. The motor has its own external ground circuit.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This step inspects for voltage through the axle minifuse.
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This step inspects for voltage and ground at the motor.
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This step inspects for voltage and ground at the relay.
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This step inspects for output voltages on the secondary side of the relay.
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This step inspects for voltages at the relay.
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This step inspects the integrity of the switch.
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Two-Speed Rear Axle Schematics | |||
1 | Did you review the Two-Speed Rear Axle Shift System Description and Operation and perform the necessary inspections? | Go to Step 2 | Go to Two Speed Rear Axle Shift System Description and Operation |
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 |
Turn the ignition switch to RUN. Using a test lamp, inspect for voltage at the axle fuse in the minifuse box. Does the test lamp illuminate? | Go to Step 4 | Go to Step 10 | |
Inspect for voltage and ground at the motor.
Did the test lamp illuminate on both tests? | Go to Step 15 | Go to Step 5 | |
Using a test lamp, test for voltage and ground at the relay connector.
Did the test lamp illuminate on both tests? | Go to Step 6 | Go to Step 7 | |
Test for voltage on the secondary side of the relay.
Did the test lamp light on both tests? | Go to Step 9 | Go to Step 13 | |
Test for voltage to the relay at both ignition 3 voltage circuits. Did the test lamp illuminate on both tests? | Go to Step 8 | Go to Step 11 | |
Do you have continuity? | Go to Step 12 | Go to Step 14 | |
9 | Repair the open or short to ground in the shift motor control high gear circuit or the shift signal circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 16 | -- |
10 | Repair the open or short to ground in the ignition 3 voltage circuit leading to the axle fuse or replace the fuse. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 16 | -- |
11 | Repair the open or short to ground in the ignition 3 voltage circuit between the axle fuse and the relay. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 16 | -- |
12 | Repair the open in the relay ground circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 16 | -- |
13 | 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 16 | -- |
14 | Replace the two-speed rear axle shift switch. Refer to Two Speed Rear Axle Shift Control Switch Replacement . Did you complete the replacement? | Go to Step 16 | -- |
15 | 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 16 | -- |
16 | Test drive the vehicle and operate the two-speed rear axle system as described in the supporting text. Does the symptom occur? | Go to Step 3 | System OK |
