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 Exhaust Solenoid Control Circuit | C0660 06 | C0660 06 | C0660 01 | -- |
Automatic Level Control Exhaust Solenoid Supply Voltage Circuit | C0660 06 | C0660 06 | -- | -- |
Automatic Level Control Relay Coil Control Circuit | C0712 06 | C0712 06 | C0712 01 | -- |
Automatic Level Control Relay Coil Supply Voltage Circuit | C0712 06 | C0712 06 | -- | -- |
Automatic Level Compressor Control Circuit | 2 | 2 | 1 | -- |
Automatic Level Control Compressor Ground Circuit | -- | 2 | -- | -- |
1. Rear of Vehicle High 2. Rear of Vehicle Low | ||||
Circuit/System Description
The Automatic Level Control (ALC) System uses the electronic suspension control module (ESCM), level sensors, compressor, and exhaust valve to increase or decrease air pressure in the system to control trim height. Battery voltage is supplied to the exhaust valve and compressor relay. The ESCM controls the ground circuits that activate the exhaust valve and compressor relay which maintain trim height based on the level sensor input voltage.
Diagnostic Aids
Performing the Suspension Position Calibration procedure may correct the condition.
Reference Information
Schematic Reference
Automatic Level Control Schematics
Connector End View Reference
Description and Operation
Automatic Level Control Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for Scan Tool Information
Circuit/System Verification
Ignition ON, command the exhaust valve solenoid ON and OFF with a scan tool. Listen for the exhaust valve clicking.
Circuit/System Testing
- Ignition OFF, disconnect the harness connector at the ALC compressor.
- Ignition ON, verify that a test lamp illuminates between the ALC compressor connector B+ circuit terminal B and ground.
- Connect a test lamp between the ALC compressor connector control circuit terminal C and the B+ circuit terminal B.
- Command the exhaust valve solenoid ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
- If all circuits test normal, test or replace the ALC compressor.
| ⇒ | 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 and the ESC/ALC EXH fuse is open, test the exhaust valve control circuit for a short to ground. If all circuits test normal, test or replace the ALC compressor. |
| ⇒ | If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the ESCM. |
| ⇒ | If the test lamp is always OFF, test the control circuit for an open/high resistance. If the circuit tests normal, replace the ESCM. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for electronic suspension control module (ESCM) replacement, programming and setup |
