The automatic level control (ALC) adjusts the vehicle suspension ride height. The electronic suspension control (ESC) module determines the height of the vehicle based on the signal from the rear height sensors. The ESC raises and lowers the vehicle in order to keep the vehicle level.

The exhaust valve control circuit is shorted to voltage, ground, or open.

The ALC will be inoperative.

Ignition ON, command the Automatic Level Control (ALC) exhaust solenoid valve ON and OFF with a scan tool. The exhaust solenoid valve should turn ON and OFF with each command.

1. Ignition OFF, disconnect the automatic level control (ALC) compressor.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal A and ground.

⇒	If the test lamp illuminates, test the control circuit for a short to voltage.

3. Verify that a test lamp illuminates between the B+ circuit terminal C and ground.

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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 MDL fuse is open, test the control circuit for a short to ground. If the circuit tests normal, test or replace the automatic level control (ALC) compressor assembly.

4. Connect a test lamp between the B+ circuit terminal C and the control circuit terminal A.
5. Command the exhaust 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 ESC module.

⇒	If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ESC module.