SCHEMATIC REFERENCE: Automatic Level Control Schematics

Did you perform the ALC Diagnostic System Check?

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Go to Step 2

Go to Automatic Level Control Diagnostic System Check

1. Install a scan tool.
2. Turn ON the ignition, with the engine OFF.
3. With the scan tool, observe the suspension position sensor parameter in the rear integration module (RIM) and record the voltage value displayed.
4. Using the scan tool, command the ALC exhaust solenoid to open, to vent the system (an audible hiss sound may be heard).

Did the ALC system vent and the vehicle lower?

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Go to Step 3

Go to Step 15

Did the suspension position sensor parameter voltage change?

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Go to Step 8

Go to Step 4

Important: A false DTC may be set.

1. Disconnect the suspension position sensor harness connector.
2. With a scan tool, observe the suspension position sensor parameter.

Does the suspension position sensor reading indicate 0 volts?

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Go to Step 5

Go to Step 9

1. Turn OFF the ignition.
2. Disconnect the suspension position sensor.
3. Turn ON the ignition, with the engine OFF.
4. Measure the voltage from the suspension position sensor 5 volt signal circuit to a good ground.

Does the voltage measure near the specified value?

5 V

Go to Step 6

Go to Step 10

1. Turn OFF the ignition.
2. Connect a 3 amp fused jumper wire between the 5 volt signal circuit and the 5 volt reference circuit of the suspension position sensor.
3. Turn ON the ignition, with the engine OFF.
4. Measure the voltage between the suspension position sensor 5 volt signal circuit and the suspension position sensor 5 volt reference circuit.

Does the voltage measure greater than the specified value?

4.75 V

Go to Step 7

Go to Step  11

1. Turn OFF the ignition.
2. Disconnect the fused jumper wire.
3. Turn the ignition ON, with the engine OFF.
4. Measure the voltage between the suspension position sensor 5 volt signal circuit and suspension position sensor ground circuit.

Does the voltage measure near the specified value?

4.75 V

Go to Step  13

Go to Step 12

Perform the ALC relearn procedure. Refer to ALC Trimset under Chassis/Output Controls/Recalibration.

Did you complete the procedure?

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Go to Step 23

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Test the 5 volt reference circuit of the suspension position sensor for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

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Go to Step 23

Go to Step 14

Test the 5 volt signal circuit of the suspension position sensor for a short to ground, high resistance or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

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Go to Step 23

Go to Step 14

Test the 5 volt reference circuit of the suspension position sensor for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

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Go to Step 23

Go to Step 14

Test the ground circuit of the suspension position sensor for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

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Go to Step 23

Go to Step 14

Inspect for poor connections at the harness connector of the suspension position sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

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Go to Step 23

Go to Step 20

Inspect for poor connections at the harness connector of the RIM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

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Go to Step 23

Go to Step 22

Important: The vehicle must be raised on a drive on lift. Full vehicle weight must be on the rear tires.

1. Raise and support the vehicle.
2. Disconnect the air tube assembly from the air dryer.

Did the ALC system vent and the vehicle lower?

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Go to Step 16

Go to Step 17

Inspect for poor connection/terminal tension at the harness connector of the Automatic Level Control Compressor Assembly. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

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Go to Step 23

Go to Step 21

Disconnect the air tube assembly from both shock absorbers.

Did the vehicle lower?

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Go to Step 18

Go to Step 19

Replace the air tube assembly. Refer to Air Tube Replacement .

Did you complete the replacement?

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Go to Step 23

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Replace the shock that did not lower. Refer to Shock Absorber Replacement in Rear Suspension.

Did you complete the replacement?

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Go to Step 23

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Replace the suspension position sensor. Refer to Automatic Level Control Sensor Replacement .

Did you complete the replacement?

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Go to Step 23

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Replace the automatic level control compressor head assembly. Refer to Air Compressor Replacement .

Did you complete the replacement?

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Go to Step 23

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Replace the RIM. Refer to Rear Integration Body Control Module Replacement in Body Control Systems.

Did you complete the replacement?

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Go to Step 23

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Operate the vehicle within the conditions for enabling the automatic level control.

Does the ALC operate correctly?

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System OK

Go to Step 2

SCHEMATIC REFERENCE: Automatic Level Control Schematics

Did you perform the Automatic Level Control (ALC) Diagnostic System Check?

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Go to Step 2

Go to Automatic Level Control Diagnostic System Check

1. Turn the ignition ON with the engine OFF.
2. Listen for the ALC air compressor to activate.

Is the ALC air compressor running for more than 5 minutes?

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Go to Step 3

Go to Step 6

1. Turn the ignition OFF.
2. Remove the ALC compressor relay.
3. Turn the ignition ON with the engine OFF.

Is the air compressor running?

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Go to Step 4

Go to Step 5

1. Turn the ignition OFF.
2. Reinstall the ALC compressor relay.
3. Repair the short to voltage in the ALC air compressor control circuit.

Is the repair complete?

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Go to Step 13

Go to Step 1

1. Turn the ignition OFF.
2. Replace the ALC air compressor relay.

Is the repair complete?

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Go to Step 13

Go to Step 1

Inspect the left and right rear position sensors for damage and disconnected links.

Are any damaged sensors or disconnected links present?

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Go to Step 7

Go to Step 8

Replace the damaged rear position sensor or reconnect the link.

Is the repair complete?

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Go to Step 13

Go to Step 1

Important: Do not remove the ALC intake filter from the ALC air compressor or hose.

1. Remove the ALC intake filter from the vehicle body .
2. Using the scan tool, cycle ALC air compressor.
3. After 1 minute, stop cycling.
4. Cycle the ALC exhaust while checking to see if air is exiting the ALC intake air filter.

Is air exiting the ALC intake air filter?

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Go to Step 11

Go to Step 9

1. Stop exhausting.
2. Disconnect the air tubes from both rear shock absorbers.
3. Connect the J 22124-B to both (between) the air tubes.
4. Open the gage toggle valve.
5. Disconnect the air tube from the ALC air dryer.
6. Apply shop air to the gage schrader valve.

Is air exiting both of the air tubes at the ALC air dryer connection?

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Go to Step 10

Go to Step 12

1. Turn the ignition OFF.
2. Replace the ALC air compressor assembly. Refer to Air Compressor Replacement .
3. Install the ALC intake air filter on the vehicle body.

Are all of the replacements and/or installations complete?

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Go to Step 13

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1. Turn the ignition OFF.
2. Connect the scan tool.
3. Turn the ignition ON with the engine OFF.
4. Preform the ALC Trim Height Adjustment. Refer to Trim Height Adjustment.

Has the ALC Trim Height Adjustment been completed?

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Go to Step 13

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Replace the air tube going from the air dryer to both rear shock absorbers. Refer to Air Tube Replacement .

Is the repair complete?

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Go to Step 13

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1. Turn the ignition OFF
2. Turn the ignition ON with the engine OFF
3. Wait for at least 5 minutes.

Is the rear of the vehicle trim (level)?

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Go to Step 14

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Operate the system in order to verify the repair.

Did you correct the condition?

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System OK

Go to Step 1