GM Service Manual Online
For 1990-2009 cars only

Step

Action

Value(s)

Yes

No

1

  1. Check vehicle trim height.
  2. Reset the automatic level control (ALC) system by cycling the ignition.
  3. Place a 136 kg (300 lb) weight in the rear compartment.
  4. Turn the ignition switch to the ON position.
  5. Check the operation of the rear suspension leveling air compressor.

Does the compressor activate after 25 seconds?

--

Go to Step 2

Go to Step 9

2

Did the compressor remain active longer than 3 minutes?

--

Go to Step 3

Go to Step 4

3

Go to the Automatic Level Control System Operation Check for diagnosis.

Is the repair procedure complete?

--

System OK

--

4

Did the rear of the vehicle return to the original trim height?

--

Go to Step 6

Go to Step 5

5

Go to Height Sensor Operational Check for diagnosis.

Is the repair procedure complete?

--

System OK

--

6

  1. Remove the 136 kg (300 lb) weight from the rear compartment.
  2. Check the operation of the exhaust solenoid valve.

Does the valve activate after 25 seconds?

--

Go to Step 7

Go to Step 9

7

Check the vehicle trim height after 5 minutes.

Did the rear of the vehicle return to the original trim height?

--

Go to Step 9

Go to Step 8

8

Go to Automatic Level Control Compressor Inoperative - No DTC Set for diagnosis.

Is the repair procedure complete?

--

System OK

--

9

  1. Turn the ignition switch to the OFF position.
  2. Install the scan tool.
  3. Establish communication with the Automatic Level Control (ALC) Sensor.

Does the scan tool communicate with the ALC Sensor?

--

Go to Step 11

Go to Step 10

10

Go to Scan Tool Does Not Communicate with Automatic Level Control Sensor for diagnosis.

Is the repair procedure complete?

--

System OK

--

11

Are any current DTCs displayed?

--

Go to Step 12

Go to Step 13

12

Go to the Diagnostic Trouble Code (DTC) List/Type for the applicable DTC for diagnosis.

Is the repair procedure complete?

--

System OK

--

13

Are any history or intermittent DTCs displayed?

--

Go to Step 14

System OK

14

  1. There is an intermittent problem within the system.
  2. Go to the Diagnostic Aids relating to the DTC for diagnosis.

Is the repair procedure complete?

--

System OK

--