GM Service Manual Online
For 1990-2009 cars only

Step

Action

Yes

No

Schematic Reference: Automatic Level Control Schematics

1

Did you perform the Automatic Level Control Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - Automatic Level Control

2

Is the rear of the vehicle low?

Go to Step 3

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

3

Inspect all air tubes and fittings for leaks.

Did you find and correct the condition?

Go to Step  12

Go to Step  4

4

  1. Connect a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. Use the scan tool to turn ON and OFF the compressor motor.

Does the compressor turn ON and OFF with each command?

Go to Step  5

Go to Step  7

5

  1. Turn OFF the ignition.
  2. Disconnect the compressor motor relay.
  3. Probe the battery positive voltage circuit of the compressor relay with a test lamp that is connected to a good ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Does the test lamp illuminate?

Go to Step  6

Go to Step  7

6

Connect a 20A fused jumper wire between the battery positive voltage circuit of the compressor motor relay and the compressor control circuit of the compressor motor relay.

Does the compressor motor turn on?

Go to Step  11

Go to Step  8

7

Test the compressor control circuit of the compressor motor relay for an open, short to ground and high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step  12

Go to Step  8

8

Test the positive battery voltage circuit of the compressor motor for an open and high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step  12

Go to Step  9

9

Test the ground circuit of the compressor motor for an open and high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step  12

Go to Step  10

10

Replace the compressor leveling module. Refer to Air Compressor Replacement .

Did you complete the replacement?

Go to Step  12

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11

Replace the compressor motor relay.

Did you complete the replacement?

Go to Step  12

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12

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 3