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.

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

Ignition ON, command the exhaust valve solenoid ON and OFF with a scan tool. Listen for the exhaust valve clicking.

1. Ignition OFF, disconnect the harness connector at the ALC compressor.
2. Ignition ON, verify that a test lamp illuminates between the ALC compressor connector B+ circuit terminal C and ground.

⇒	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 ELC fuse is open, replace the ALC compressor.

3. Connect a test lamp between the ALC compressor connector control circuit terminal A and the B+ circuit terminal C.
4. 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 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.

5. If all circuits test normal, test or replace the ALC compressor.

1. Install any components or connectors that have been removed or replaced during diagnosis.
2. Perform any adjustment, programming or setup procedures that are required when a component or module is removed or replaced. This would include the Suspension Position Calibration procedure.
3. Clear the DTCs.
4. Turn OFF the ignition for 60 seconds.
5. Turn ON the ignition.
6. If the repair was related to a DTC, duplicate the Conditions for Running the DTC and use the Freeze Frame/Failure Records, if applicable, in order to verify the DTC does not reset. If the DTC resets or another DTC is present, refer to the Diagnostic Trouble Code (DTC) List - Vehicle and perform the appropriate diagnostic procedure.