• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
• | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
• | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
---|---|---|---|---|
Automatic Level Control Exhaust Solenoid B+ | C0660 06 | C0660 06 | -- | -- |
Automatic Level Control Exhaust Solenoid Control | C0660 06 | C0660 06 | C0660 01 | -- |
Automatic Level Control Relay Coil B+ | C0712 06 | C0712 06 | -- | -- |
Automatic Level Control Relay Coil Control | C0712 06 | C0712 06 | C0712 01 | -- |
Automatic Level Compressor Control | 2 | 2 | 1 | -- |
Automatic Level Control Compressor Ground | -- | 2 | -- | -- |
1. Rear of Vehicle High 2. Rear of Vehicle Low |
The automatic level control (ALC) System uses the electronic suspension control module (ESCM), level sensors, compressor, and exhaust valve to increase or decrease air pressure in the system to control trim height. Battery voltage is supplied to the exhaust valve and compressor relay. The ESCM controls the ground circuits that activate the exhaust valve and compressor relay which maintain trim height based on the level sensor input voltage.
Inspect for:
• | Leaking lines or components. Perform the Automatic Level Control System Leak Test and Air Compressor Leak Test as necessary. |
• | Performing the Suspension Position Calibration procedure may correct the condition. |
Automatic Level Control Schematics
Automatic Level Control Description and Operation
Control Module References for scan tool information
Ignition ON, command the compressor relay ON and OFF with a scan tool. Listen for the compressor running or relay clicks.
Important: Whenever repairing and/or replacing ALC system components, perform the Suspension Position Calibration procedure.
⇒ | If the test lamp illuminates, test the control circuit for a short to voltage. |
⇒ | 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 R8 for a short to ground or faulty ALC compressor motor. If all circuits test normal, test or replace the ELC relay. |
⇒ | If the test lamp does not illuminate, test the B+ circuit for an open/high resistance. |
⇒ | If greater than 1 ohm, test the ground circuit for an open/high resistance. |
⇒ | 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. |
⇒ | If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the ESCM. |
⇒ | 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 ESCM. |
⇒ | If the compressor does not run, test or replace the relay. |
⇒ | 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 fuse is open, test or replace the ALC compressor. |
⇒ | If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the ESCM. |
⇒ | If the test lamp is always OFF, test the control circuit for an open/high resistance. If the circuit tests normal, replace the ESCM. |
⇒ | If the resistance is not within the specified range, replace the relay. |
• | 30 and 86 |
• | 30 and 87 |
• | 30 and 85 |
• | 85 and 87 |
⇒ | If not the specified value, replace the relay. |
⇒ | If greater than the specified range, replace the relay. |
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
• | Control Module References for electronic suspension control module (ESCM) replacement, setup, and programming |