The electronic suspension control module (ESCM) adjusts the vehicle suspension ride height. The ESCM determines the height of the vehicle based on the voltage from the suspension position sensors. The module grounds the ELC relay and the exhaust control solenoid to raise and lower the vehicle in order to keep the vehicle level.

The compressor relay control circuit is shorted to voltage, ground, or open for 5 seconds.

The automatic level control (ALC) system will be inoperative.

The ESCM does not detect a failure during the self test.

This circuit is monitored during every functional operation of the compressor relay output and every 3.3 milliseconds when output is active. If a compressor relay fault is detected, the ESCM retries the output every 15 seconds to try to recover from the fault.

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 compressor relay ON with a scan tool. Listen for the operation of the ELC relay and the automatic level control compressor.

1. Ignition OFF, disconnect the ELC relay from the rear fuse block.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 12 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 relay B+ circuit terminal 14 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 B+ circuit fuse is open, test the control circuit terminal 12 for a short to ground or faulty ALC compressor motor. If all circuits test normal, test or replace the ELC relay.

4. Verify that a test lamp illuminates between the relay B+ circuit terminal 15 and ground.

⇒	If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.

5. Disconnect the harness connector at the air compressor.
6. Test for less than 1 ohm of resistance between the ALC compressor ground circuit terminal D and ground.

⇒	If greater than 1 ohm, test the ground circuit for an open/high resistance.

7. Connect the harness connector at the ALC compressor.
8. Connect a 40A fused jumper wire between the relay B+ circuit terminal 14 and the control circuit terminal 12. Verify the ALC compressor is activated.

⇒	If the ALC compressor does not activate, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the ALC compressor.

9. Connect a test lamp between the B+ circuit terminal 15 and the control circuit terminal 11.
10. Command the ALC compressor relay 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 electronic suspension control 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 electronic suspension control module.

11. If all circuits test normal, test or replace the ELC relay.

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.