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 voltage from the ALC sensor. The ESC module grounds the ELC COMPRSR relay and the exhaust control solenoid to raise and lower the vehicle in order to keep the vehicle level. The relay control 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 ESC module retries the output every 15 seconds to try to recover from the fault.

The compressor relay output is shorted to voltage, ground, or open for 10 seconds.

The ALC will be inoperative.

The ESC module does not detect a failure during the self test.

Schematic Reference

Automatic Level Control Schematics

Connector End View Reference

Automatic Level Control Connector End Views

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 COMPRSR relay and the ALC compressor.

1. Ignition OFF, disconnect the ELC COMPRSR relay.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 11 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 15 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 COMPRSR fuse is open, test the control circuit terminal 12 for a short to ground. If the circuit tests normal, test or replace the ELC COMPRSR relay.

4. Connect a test lamp between the B+ circuit terminal 15 and the control circuit terminal 11.
5. Command the ELC COMPRSR 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 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.

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

Relay Test

1. Ignition OFF, disconnect the ELC COMPRSR relay.
2. Test for 40-200 ohms of resistance between terminals 85 and 86.

⇒	If the resistance is not within the specified range, replace the relay.

3. Test for infinite resistance between the following terminals:

•

30 and 86

•

30 and 87

•

30 and 85

•

85 and 87

⇒	If not the specified value, replace the relay.

4. Test for less than 2 ohms of resistance between terminals 30 and 87A.

⇒	If greater than the specified range, replace the relay.

5. Install a 3 amp fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms of resistance between terminals 30 and 87.

⇒	If greater than the specified range, replace the relay.