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For 1990-2009 cars only

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.

  1. This step tests for proper ignition 3 voltage at the two-speed rear axle air shift switch.

  2. This step tests for proper operation of the two-speed rear axle air shift switch.

  3. This step tests for proper operation of the two-speed rear axle air shift switch.

  4. This step tests the ignition 3 voltage circuit for an open or high resistance.

  5. 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

Go to Symptoms - Rear Drive Axle

2

Verify the fault is present.

Does the system operate normally?

--

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 3

3

  1. Turn ON the ignition, with the engine OFF.
  2. Disconnect the two-speed rear axle air shift switch connector.
  3. Test the ignition 3 voltage circuit for proper voltage.

Does the voltage measure within the specified value?

9-14 V

Go to Step 4

Go to Step 6

4

  1. Verify the two-speed rear axle shift control valve is in the LOW position.
  2. Disconnect the two-speed rear axle air shift switch connector.
  3. Test the two-speed rear axle air shift switch for continuity.

Is continuity present across the switch?

--

Go to Step 5

Go to Step 8

5

  1. Place the shift control valve in the HIGH position.
  2. Test the two-speed rear axle air shift switch for continuity.

Is continuity present across the switch?

--

Go to Step 8

Go to Step 7

6

Test for an open or high resistance in the ignition 3 voltage circuit. Refer to Circuit Testing and Wiring Repairs .

Did you complete the repair?

--

Go to Step 9

--

7

Repair the open, high resistance, or short to ground in the air shift switch signal circuit. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 9

Go to Speedometer and/or Odometer Inaccurate or Inoperative

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.

  1. This step inspects for voltage through the axle minifuse.

  2. This step inspects for voltage and ground at the motor.

  3. This step inspects for voltage and ground at the relay.

  4. This step inspects for output voltages on the secondary side of the relay.

  5. This step inspects for voltages at the relay.

  6. 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

Go to Step 3

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

4

Inspect for voltage and ground at the motor.

  1. Disconnect the connector at the motor.
  2. Connect a test lamp between terminal C and B.
  3. Observe the test lamp.
  4. Connect a test lamp between terminal A and B.
  5. Have a helper move the switch to HI range while the technician observes the test lamp.

Did the test lamp illuminate on both tests?

Go to Step 15

Go to Step 5

5

Using a test lamp, test for voltage and ground at the relay connector.

  1. Turn the ignition switch OFF.
  2. Connect the motor connector.
  3. Disconnect the relay connector.
  4. Turn the ignition switch to RUN.
  5. Connect the test lamp between terminal 85 and 86.
  6. Observe the test lamp.
  7. Connect the test lamp between terminal 85 and 30.
  8. Observe the test lamp.

Did the test lamp illuminate on both tests?

Go to Step 6

Go to Step 7

6

Test for voltage on the secondary side of the relay.

  1. Turn the ignition switch to OFF.
  2. Connect the relay.
  3. Turn the ignition switch to RUN.
  4. Connect the test lamp to a known ground.
  5. Back probe the shift motor control high gear circuit at the relay while observing the test lamp.
  6. Turn the switch to LOW.
  7. Back probe the shift signal circuit while observing the test lamp.

Did the test lamp light on both tests?

Go to Step 9

Go to Step 13

7

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

8

  1. Turn the ignition switch to OFF.
  2. Turn the two-speed rear axle switch to LOW.
  3. Connect the relay.
  4. Disconnect the two-speed rear axle switch.
  5. Put the two-speed rear axle switch in HI.
  6. Using a DMM, test for continuity on the closed switch.

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 .

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 .

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 .

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 .

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