GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The automatic level control sensor monitors the compressor relay coil control circuity for a short to ground.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC 021 Compressor Relay Circuit Short to Ground

Conditions for Running the DTC

The ignition is ON.

Conditions for Setting the DTC

This DTC is set when the automatic level control sensor detects the compressor relay coil control circuit is shorted to ground.

Action Taken When the DTC Sets

    • The automatic level control sensor disables the compressor.
    • The automatic level control sensor disables inflator functions.
    • Lowering functions shall continue.

Conditions for Clearing the DTC

    • The conditions that caused the DTC to set have been removed.
    • The ignition has transitioned from OFF to ON.

Diagnostic Aids

    • Compressor motor will run continuously.
    • When this occurs, DTC 023 will be set.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step tests for short to ground in compressor relay control circuit.

  2. This step verifies that the automatic level control sensor is self tested after replacement.

Step

Action

Yes

No

Schematic Reference: Automatic Level Control Schematics

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

Test the control circuit of the compressor relay for a short to ground. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 4

Go to Step 3

3

Important: System untested codes will continue to flash until the self test has been completed after automatic level control sensor replacement .

Replace the automatic level control sensor. Refer to Automatic Level Control Sensor Replacement .

Did you complete the replacement?

Go to Step 4

--

4

Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

Go to Step 2

System OK