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

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

The air suspension will be inoperative.

The ASCM 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 ASCM retries the output every 15 seconds to try to recover from the fault.

Schematic Reference

Air Suspension Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Air Suspension Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

Ignition ON, command the compressor relay ON with a scan tool. Listen for the operation of the ECAS relay and the air suspension compressor.

1. Ignition OFF, disconnect the ECAS relay.
2. Test for less than 2.0 ohms between the relay ground circuit terminal 86 and ground.

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

3. Ignition ON, verify that a test lamp does not illuminate between the ECAS relay control circuit terminal 30 and ground.

⇒	If the test lamp illuminates, test the control circuit terminal 30 for a short to voltage.

4. Verify that a test lamp illuminates between the ECAS relay underhood fuse block B+ circuit terminal 87 and ground.

⇒	If the test lamp does not illuminate, test the relay B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the air suspension control module.

5. Connect a test lamp between the ECAS relay B+ circuit terminal 87 and the control circuit terminal 30.
6. Command the 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 air 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 air suspension control module.

7. If all circuits test normal, test or replace the ECAS relay.

Relay Test

1. Ignition OFF, disconnect the ECAS Relay.
2. Test for 0-2 ohms 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. Install a 40A fused jumper between the relay 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less then 2.0 ohms between terminals 30 and 87.

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

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.