GM Service Manual Online
For 1990-2009 cars only

Diagnostic Instructions

    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

Automatic Level Control (ALC) Inflator Solenoid Valve B+

1

1

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Automatic Level Control (ALC) Inflator Solenoid Control

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1

--

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1. Automatic Level Control (ALC) Solenoid Valve Inoperative

Diagnostic Aids

Review the automatic level control (ALC) system Description and Operation. Refer to Automatic Level Control Description and Operation .

Reference Information

Schematic Reference

Automatic Level Control Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

Ignition ON, press the accessory inflator switch continuously for 3 seconds. This activates the ALC self test of the rear shocks. The rear of the vehicle will rise, and then hold the rear of the vehicle up for a calibrated amount of time, to check for leaks, and then lower the rear of the vehicle to trim height. The total self test time is 200 seconds.

Circuit/System Testing

  1. Ignition OFF, disconnect the air inflator air switch harness connector at the ALC sensor.
  2. Ignition ON, connect a 10A fused jumper wire between the ALC relay inflation timer relay coil control terminal 85 and the ground circuit terminal of the air inflator switch.
  3. Verify that a test lamp illuminates between the B+ circuit terminal A and ground.
  4. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the ALC compressor relay.
  5. Ignition OFF, disconnect the ALC solenoid valve harness connector at the ALC sensor.
  6. Verify that a test lamp illuminates between the ALC solenoid valve B+ circuit terminal B and ground.
  7. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the ALC solenoid valve.
  8. Verify that a test lamp illuminates between the ALC inflator solenoid valve B+ circuit terminal B and the ALC inflator solenoid valve ground terminal A.
  9. If the test lamp illuminates, test or replace the ALC air inflator solenoid valve.
    If the test lamp does not illuminate, test the ground circuit for open/high resistance.
  10. If all circuits test normal, test or replace the air inflator solenoid valve.

Component Testing

  1. Ignition OFF, disconnect the ALC solenoid valve harness connector at the automatic level control sensor.
  2. Test for 0-2 ohms between the signal terminal B and the low reference circuit terminal A.
  3. If not within the specified range, replace the ALC air inflator solenoid.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Automatic Level Control Relay Replacement
    •  Inflator Solenoid Replacement