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Air Suspension Malfunction




Air Suspension Malfunction

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.

Diagnostic Fault Information





Circuit/System Description

The air suspension system uses level sensors, a control module, compressor, pressure sensor, right and left pressure valves, and exhaust valve to increase or decrease air pressure in the system to control trim height. The air suspension control module supplies battery voltage to the exhaust valve, pressure valves, and compressor relay. The air suspension control module also controls the ground circuits that activate the exhaust valve, pressure valves, and compressor relay which maintain trim height based on the level sensor input voltage.

Diagnostic Aids

* If the compressor runs continuously, inspect the system for any leaks or damaged components.
* Performing the Suspension Position Calibration (Programming and Relearning) procedure may correct the condition.

Reference Information
Schematic Reference

Automatic Level Control Schematics (Automatic Level Control)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

Automatic Level Control Description and Operation (W/O F55) (Automatic Level Control Description and Operation (W/O F55))Automatic Level Control Description and Operation (With F55) (Automatic Level Control)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information

Circuit/System Verification

1. Ignition ON, command the Compressor Relay ON and OFF with a scan tool. Verify that the compressor turns ON and OFF with each command.

• If the compressor does not operate or operates continuously, refer to Compressor Malfunction.

2. Ignition ON, command the exhaust valve ON and OFF with a scan tool. Verify the exhaust valve clicks and the vehicle height changes with each command.

• If the exhaust valve does not click or the vehicle height does not change, refer to Exhaust Valve Malfunction.

3. Ignition ON, command the LR and RR Control Valves ON and OFF with a scan tool. Verify the control valves click and the vehicle applicable rear corner height changes with each command.

• If a control valve does not click or the applicable rear corner height does not change, refer to Control Valve Malfunction.

Circuit/System Testing

Compressor Malfunction
1. Ignition OFF, disconnect the harness connector at the leveling compressor.
2. Test for less than 1 ohm between the compressor ground circuit terminal and ground.

• If greater than the specified range, test the ground circuit for an open/high resistance. If the circuit tests normal, test or replace the air compressor assembly.

3. Connect the test lamp between the control circuit terminal and ground.
4. Ignition ON, command the compressor relay ON and OFF with the scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

• If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ELC MDL fuse is open, test or replace the ALC compressor assembly. If the circuit tests normal and the ELC MDL fuse is not open, test or replace the ELC compressor relay.
• If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, test or replace the ELC compressor relay.

5. Test or replace the air compressor.

Exhaust Valve Malfunction
1. Ignition OFF, connect a test lamp between the exhaust valve connector control circuit terminal and the B+ circuit terminal.
2. Ignition ON, command the exhaust valve 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 an open/high resistance. If the circuit tests normal, replace the air suspension control module.

3. If all circuits test normal, test or replace the air suspension compressor assembly.

Control Valve Malfunction
1. Ignition OFF, connect a test lamp between the affected control valve connector control circuit terminal and the B+ circuit terminal.
2. Ignition ON, command the affected control valve 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 an open/high resistance. If the circuit tests normal, replace the air suspension control module.

3. If all circuits test normal, test or replace the air suspension compressor assembly.

Component Testing

1. Ignition OFF, disconnect the relay.
2. Test for 50-200 ohms between terminals 85 and 86.

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

4. Install a 20A fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2.0 ohms between terminals 30 and 87.

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

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Suspension Position Calibration (Programming and Relearning)
* Automatic Level Control Air Compressor Replacement (Automatic Level Control Air Compressor Replacement)
* Compressor Assembly Automatic Level Control Air Replacement (Compressor Assembly Automatic Level Control Air Replacement)
* Air Spring Replacement (Service and Repair)
* Air Suspension Air Line Replacement (Air Suspension Air Line Replacement)
* Relay Replacement (Attached to Wire Harness) (Relay Replacement (Attached to Wire Harness))Relay Replacement (Within an Electrical Center) (Relay Replacement (Within an Electrical Center))
* Control Module References (Programming and Relearning) for air suspension control module replacement, setup and programming

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