GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2007 🢒 Avalanche - 2WD 🢒 Driver Information and Entertainment 🢒 Cellular, Entertainment, and Navigation 🢒 DTC C0660

Diagnostic Instructions
    • 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.

DTC Descriptors

DTC C0660 01: Level Control Exhaust Valve Circuit Short to Voltage

DTC C0660 06: Level Control Exhaust Valve Circuit Short to Ground or Open

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.

Conditions for Running the DTC

C0660 01

    • The ignition is ON.
    • The exhaust valve is commanded ON.

C0660 06

    • The ignition is ON.
    • The exhaust valve is commanded OFF.

Conditions for Setting the DTC

C0660 01

The exhaust valve or the circuits to the valve are shorted to voltage.

C0660 06

The exhaust valve or the circuits to the valve are shorted to ground, or open.

Action Taken When the DTC Sets

C0660 01, C0660 06

    • DTC C0660 is stored in memory.
    • The driver information center (DIC) displays the SERVICE SUSPENSION SYSTEM message after 3 consecutive ignition ON cycles.
    • The ALC system is disabled.

Conditions for Clearing the DTC
    •  A current DTC will clear when the malfunction is no longer present.
    • The history DTC will clear after 100 fault-free ignition cycles.

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.
    3. ⇒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, test or replace the air compressor.
  3. Connect a test lamp between the control circuit terminal C and the Ignition circuit terminal B.
  4. With a scan tool, clear all ALC DTCs.
  5. 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.
    6. ⇒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.
  6. If all circuits test normal, replace the air compressor.

Component Testing
  1. Ignition OFF, disconnect the air compressor harness connector.
  2. Test the exhaust valve for 18-45 ohms between the control terminal and the battery positive terminal.
    3. ⇒If resistance is not within the specified range, replace the air compressor.
  3. Test for infinite resistance between the control terminal and ground.
    4. ⇒If less than infinite resistance, replace the air compressor.

Repair Instructions

Air Compressor Replacement

Control Module References for ESCM replacement, setup, and programming

Repair Verification
  1. Install any components or connectors that have been removed or replaced during diagnosis.
  2. Perform any adjustment, programming or setup procedures that are required when a component or module is removed or replaced.
  3. Clear the DTCs.
  4. Use the scan tool Diagnostic Counter Reset output control function to bypass the 3 consecutive ignition cycle requirement for setting a DTC. This will ensure that if a DTC was to be reset during the repair verification process, it will be displayed on the scan tool.
  5. Turn OFF the ignition for 60 seconds.
  6. Turn ON the ignition.
  7. If the repair was related to a DTC, duplicate the Conditions for Running the DTC and use the Freeze Frame/Failure Records, if applicable, in order to verify the DTC does not reset. If the DTC resets or another DTC is present, refer to the Diagnostic Trouble Code (DTC) List - Vehicle and perform the appropriate diagnostic procedure.