GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 1999 🢒 Catera 🢒 Body and Accessories 🢒 Wiring Systems 🢒 Automatic Level Control System Operation Check

Support the rear wheels or support the rear lower control arms when certain tests require raising the vehicle on a hoist. Use two additional jack stands in order to support the rear lower control arms in the normal curb weight position when a frame type hoist is used. Refer to Trim Height Specifications in Suspension General Diagnosis.

Refer to ALC Suspension System Check for electrical troubleshooting of the Automatic Level Control (ALC) system, or if DTC's are present.

Diagnosing Leveling Complaints Without DTCs Present Procedure

Perform the following preliminary inspections before performing the system performance test:

  1. Inspect the ignition (pin A & pin H) at the ALC sensor connector.
  2. Ensure that the ignition (pin A & pin H) at the ALC sensor connector connection is secure.
  3. Inspect the ground (pin E) at the ALC sensor connector.
  4. Ensure that the ground (pin E) at the ALC sensor connector connection is secure.
  5. Inspect the ALC sensor link.
  6. Ensure that the ALC sensor link is properly secured to the actuator arm.
  7. Inspect the ALC sensor actuator arm for damage.

ALC Diagnosis Table

Step

Action

Value(s)

Yes

No

1

Has the ALC compressor assembly and the air tube been replaced?

--

Go to Step 7

Go to Step 2

2
  1. Raise and support the vehicle. Lifting and Jacking the Vehicle in General Information.
  2. Inspect the air tubes running from the ALC compressor to both rear shock absorbers.
  3. Inspect the air tube connection at the ALC air dryer.

Are the air tubes damaged and/or disconnected?

--

Go to Step 13

Go to Step 3

3

Squeeze the left rear shock absorber in the middle of the air sleeve.

Did the air sleeve slightly compress?

--

Go to Step 5

Go to Step 4

4
  1. Operate the ALC system for 60 seconds.
  2. Test the air tube-to-air dryer connection for leaks using a soap bubble solution.

Is a leak evident?

--

Go to Step 20

Go to Step 5

5
  1. Disconnect the air tube from the ALC dryer.
  2. Connect the Pressure Gauge to the ALC dryer.
  3. Close the toggle valve on the Pressure Gauge .
  4. Operate the ALC compressor.

Did the pressure build to the specified value?

80 psi

Go to Step 6

Go to Step 10

6
  1. Shut off the compressor when the pressure reaches 80 psi.
  2. Monitor the gauge for 1 minute.

Did the pressure leak down?

--

Go to Step 10

Go to Step 7

7
  1. Connect the Pressure Gauge to the right rear shock absorber. Ensure that the toggle valve on the Pressure Gauge is away from the shock absorber.
  2. Close the toggle valve.
  3. Pressurize the shock absorber at the toggle valve on the Pressure Gauge to 80 psi.
  4. Monitor the gauge for 1 minute.

Did the system leak down?

--

Go to Step 11

Go to Step 8

8
  1. Use the toggle valve on the Pressure Gauge in order to slowly release the air pressure.
  2. Disconnect the Pressure Gauge from the right rear shock absorber.
  3. Connect the Pressure Gauge to the left rear shock absorber.
  4. Pressurize the Pressure Gauge to 80 psi.
  5. Monitor the gauge for 1 minute.

Did the pressure leak down?

--

Go to Step 12

Go to Step 9

9
  1. Use the toggle valve on the Pressure Gauge in order to slowly release the air pressure.
  2. Disconnect the Pressure Gauge from the left rear shock absorber.
  3. Connect the Pressure Gauge , inline, at the tee near the rear of the vehicle.
  4. Reconnect the air tube to the ALC dryer.
  5. Open the toggle valve on thePressure Gauge .
  6. Using shop air, pressurize the system to 80 psi at the service connection of the Pressure Gauge .
  7. Monitor the pressure gauge for 1 minute.

Did the pressure leak down?

--

Go to Step 14

Go to Step 20

10

Replace the following components:

    • Replace the ALC compressor. Refer to Air Compressor Replacement .
    • Replace the air tube. Refer to Air Tube Replacement .

Are the replacements complete?

--

Go to Step 20

--

11
  1. Slowly open the toggle valve on the Pressure Gauge in order to relieve the air pressure.
  2. Replace the right rear shock absorber. Refer to Shock Absorber Replacement in Rear Suspension.
  3. Reconnect all of the air tube connections.

Is the shock absorber replaced, and are all of the air tube connections reconnected?

--

Go to Step 20

--

12
  1. Slowly open the toggle valve on the Pressure Gauge in order to relieve the air pressure.
  2. Replace the left rear shock absorber. Refer to Shock Absorber Replacement in Rear Suspension.
  3. Reconnect all of the air tube connections.

Is the shock absorber replaced, and are all of the air tube connections reconnected?

--

Go to Step 20

--

13

Are any of the air tubes damaged?

--

Go to Step 14

Go to Step 18

14

Replace the air tube that runs from the air dryer to the two rear shock absorbers.

Is the replacement complete?

--

Go to Step 15

--

15
  1. Remove the ALC air dryer from the compressor assembly.
  2. Shake the ALC air dryer with the head connection down.

Did water/moisture come out of the ALC air dryer when the dryer was shaken?

--

Go to Step 16

Go to Step 17

16

Replace the ALC air dryer. Refer to Automatic Level Control Air Dryer Replacement .

Is the replacement complete?

--

Go to Step 17

--

17

Replace the air compressor head. Refer to Automatic Level Control Air Compressor Head Replacement .

Is the replacement complete?

--

Go to Step 18

--

18
  1. Install the ALC compressor on the vehicle.
  2. Reconnect all of the air tube connections.

Is the ALC compressor reinstalled, and are all of the air tube connections reconnected?

--

Go to Step 20

--

19

Repair the air tube-to-air dryer connection leak.

Is the repair complete?

--

Go to Step 20

--

20
  1. Reconnect all of the connectors that were disconnected.
  2. Reconnect all of the components that were removed.
  3. Clear all of the codes with the ignition ON and with the engine OFF.
  4. Wait at least 5 minutes.

Is the rear of the vehicle trim level?

--

System OK

--