Rear of Vehicle High

Rear of Vehicle High

Diagnostic Instructions

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

Circuit/System Description

The Automatic Level Control (ALC) System uses an exhaust valve to release air from the rear shocks to lower to trim height, or during a compressor head pressure relief cycle. Battery voltage is supplied to the valve. The electronic suspension control module (ESCM) controls the ground to activate the valve and monitors the voltage level to ensure it agrees with its command state.

Diagnostic Aids

Inspect for:

^ Damaged rear suspension position sensors.
^ Kinked or pinched lines.

Reference Information
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

^ Circuit Testing
^ Connector Repairs
^ Testing for Intermittent Conditions and Poor Connections
^ Wiring Repairs

Scan Tool Reference

^ Scan Tool Data List
^ Scan Tool Data Definitions
^ Scan Tool Output Controls

Circuit/System Verification

Ignition ON, command the exhaust valve solenoid ON and OFF with a scan tool. Listen for the exhaust valve clicking.

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the ALC compressor.
2. Ignition ON, verify that a test lamp illuminates between Ignition circuit terminal B and ground.
^ If the test lamp does not illuminate, test the Ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal and the Ignition circuit fuse is open, replace the air compressor.

3. Connect a test lamp between the control circuit terminal C and the Ignition circuit terminal B.
4. Command the exhaust valve solenoid 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 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.

5. If all circuits test normal, test or replace the air compressor.
Repair Instructions

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

^ Air Compressor Replacement
^ Control Module References for ESCM replacement, setup, and programming