Operation CHARM: Car repair manuals for everyone.
Home >> Buick >> 2011 >> Lucerne V6-3.9L >> Repair and Diagnosis >> Steering and Suspension >> Suspension >> Suspension Control ( Automatic - Electronic ) >> Testing and Inspection >> Symptom Related Diagnostic Procedures >> Rear of Vehicle Low

Rear of Vehicle Low




Rear of Vehicle Low

Diagnostic Instructions

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

Diagnostic Fault Information





Circuit/System Description

The automatic level control (ALC) system uses a combination level sensor/module, 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 ALC module controls the ground circuits that activate the exhaust valve and compressor relay which maintain trim height based on the level sensor input voltage.

Diagnostic Aids

* Inspect for leaking lines or components. Perform the Automatic Level Control System Leak Test (Automatic Level Control System Leak Test) and Air Compressor Leak Test (Air Compressor Leak Test) as necessary.
* Performing the Suspension Position Calibration (Service and Repair) 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 End Views By Name)
Description and Operation

Automatic Level Control Description and Operation (Automatic Level Control)
Electrical Information Reference

* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)

Scan Tool Reference

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

Circuit/System Verification

Ignition ON, command the compressor relay ON and OFF with a scan tool. Listen for the compressor running or relay clicks.

Circuit/System Testing

Important: Whenever repairing and/or replacing ALC system components, perform the Suspension Position Calibration procedure.


1. Ignition OFF, disconnect the ELC relay from the rear fuse block.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 87 and ground.

• If the test lamp illuminates, test the control circuit for a short to voltage.

3. Verify that a test lamp illuminates between the B+ circuit terminal 30 and ground.

• 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 87 for a short to ground or faulty ALC compressor motor. If all circuits test normal, test or replace the ELC relay.

4. Verify that a test lamp illuminates between the B+ circuit terminal 85 and ground.

• If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.

5. Disconnect the harness connector at the air compressor.
6. Test for less than 2 ohms between the ALC compressor ground circuit terminal D and ground.

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

7. Connect the harness connector at the ALC compressor.
8. Connect a 40A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the ALC compressor is activated.

• 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.

9. Connect a test lamp between the B+ circuit terminal 85 and the control circuit terminal 86.
10. Command the ALC 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 ALC sensor/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 ALC sensor/module.

11. Connect the ELC relay. Command the ALC compressor ON with a scan tool. Verify the compressor is running.

• If the compressor does not run, test or replace the relay.

12. Ignition OFF, disconnect the harness connector at the ALC compressor.
13. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal C and ground.

• 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.

14. Connect a test lamp between the control circuit terminal A and the B+ circuit terminal C.
15. 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 ALC sensor/module.
• If the test lamp is always OFF, test the control circuit for an open/high resistance. If the circuit tests normal, replace the ALC sensor/module.

16. If all circuits test normal, test or replace the ALC compressor.

Component Testing

Relay Test
1. Ignition OFF, disconnect the relay.
2. Test for 50-200 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 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.

* Relay Replacement (Service and Repair)
* Air Compressor Replacement (Service and Repair)
* Suspension Position Calibration (Service and Repair)
* Control Module References (Programming and Relearning)for automatic level control sensor/module replacement, setup and programming

pro multis · About Operation CHARM