GM Service Manual Online
For 1990-2009 cars only

Automatic Level Control System Does Not Raise Vehicle without Inflator

Step

Action

Yes

No

Schematic Reference: Automatic Level Control Schematics

1

Did you review the Automatic Level Control System Description and Operation and perform the necessary inspections?

Go to Step 2

Go to Symptoms - Automatic Level Control

2

  1. Turn ON the ignition, with the engine OFF.
  2. Add a load of 135 kg (300 lbs) to the rear of the vehicle.

Does the automatic level control (ALC) air compressor operate?

Go to Step 3

Go to Step 4

3

Does the rear of the vehicle rise and not leak down?

Go to Automatic Level Control Sensor Adjustment

Go to Automatic Level Control System Leak Test

4

  1. Disconnect the automatic level control (ALC) sensor connector.
  2. Connect a test lamp between the battery positive voltage circuit of the ALC sensor and a good ground.

Does the test lamp illuminate?

Go to Step 5

Go to Step 14

5

Connect a test lamp between the ALC height sensor circuit and the ALC sensor ground circuit.

Does the test lamp illuminate?

Go to Step 6

Go to Step 15

6

Connect a test lamp between the ALC relay coil supply voltage circuit and a good ground.

Does the test lamp illuminate?

Go to Step 7

Go to Step 8

7

Connect a 10 amp fused jumper wire between the ALC relay coil supply voltage circuit and a good ground.

Does the ALC air compressor activate?

Go to Step 20

Go to Step 10

8

Probe the ALC relay coil supply voltage circuit of the ALC relay connector with a test lamp connected to a good ground.

Does the test lamp illuminate?

Go to Step 16

Go to Step 9

9

Probe the accessory voltage circuit of the ALC relay connector with a test lamp connected to a good ground.

Does the test lamp illuminate?

Go to Step 21

Go to Step 17

10

  1. Remove the ALC air compressor relay.
  2. Connect a 10 A fused jumper wire between pin 1 and pin 4 of the ALC air compressor relay connector.

Does the ALC air compressor activate?

Go to Step 21

Go to Step 11

11

  1. Disconnect the ALC air compressor connector.
  2. Connect a test lamp between the battery positive voltage circuit of the ALC air compressor connector and ground.

Does the test lamp illuminate?

Go to Step 12

Go to Step 19

12

Connect a test lamp between the battery positive voltage circuit and the ground circuit of the ALC air compressor connector.

Does the test lamp illuminate?

Go to Step 13

Go to Step 18

13

Test the ALC compressor harness for a poor connection or an open. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs or Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 23

Go to Step 22

14

Repair the open in the battery positive voltage circuit to the ALC sensor. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 23

--

15

Repair the open in the ALC sensor ground circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 23

--

16

Repair the open in the ALC relay coil supply voltage circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 23

--

17

Repair the open in the accessory voltage circuit to the ALC relay. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 23

--

18

Repair the open in the ALC air compressor ground circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 23

--

19

Repair the open in the battery positive voltage circuit of the ALC air compressor. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 23

--

20

Replace the ALC sensor. Refer to Automatic Level Control Sensor Replacement .

Did you complete the replacement?

Go to Step 23

--

21

Replace the ALC air compressor relay.

Did you complete the replacement?

Go to Step 23

--

22

Replace the ALC air compressor. Refer to Air Compressor Replacement .

Did you complete the replacement?

Go to Step 23

--

23

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 3

Automatic Level Control System Does Not Raise Vehicle with Inflator

Step

Action

Yes

No

Schematic Reference: Automatic Level Control Schematics

1

Did you review the Automatic Level Control System Description and Operation and perform the necessary inspections?

Go to Step 2

Go to Symptoms - Automatic Level Control

2

  1. Turn ON the ignition, with the engine OFF.
  2. Add a load of 135 kg (300 lbs) to the rear of the vehicle.

Does the automatic level control (ALC) air compressor operate?

Go to Step 3

Go to Step 4

3

Does the rear of the vehicle rise and not leak down?

Go to Automatic Level Control Sensor Adjustment

Go to Automatic Level Control System Leak Test

4

  1. Disconnect the ALC sensor connector.
  2. Connect a test lamp between the automatic level control height sensor circuit and a good ground.

Does the test lamp illuminate?

Go to Step 5

Go to Step 13

5

Connect a test lamp between the ALC height sensor circuit and the ALC sensor ground circuit.

Does the test lamp illuminate?

Go to Step 6

Go to Step 18

6

Connect a test lamp between the ALC relay coil supply voltage circuit and a good ground.

Does the test lamp illuminate?

Go to Step 7

Go to Step 8

7

Connect a 10 amp fused jumper wire between the ALC relay coil supply voltage circuit and a good ground.

Does the ALC air compressor activate?

Go to Step 23

Go to Step 10

8

Probe the ALC relay coil supply voltage circuit of the ALC relay connector with a test lamp connected to a good ground.

Does the test lamp illuminate?

Go to Step 19

Go to Step 9

9

Probe the accessory voltage circuit of the ALC relay connector with a test lamp connected to a good ground.

Does the test lamp illuminate?

Go to Step 24

Go to Step 20

10

  1. Remove the ALC air compressor relay.
  2. Connect a 10 A fused jumper wire between battery positive voltage circuit and compressor signal circuit of the ALC air compressor relay connector.

Does the ALC air compressor activate?

Go to Step 24

Go to Step 11

11

  1. Disconnect the ALC air compressor connector.
  2. Connect a test lamp between the battery positive voltage circuit of the ALC air compressor and ground.

Does the test lamp illuminate?

Go to Step 12

Go to Step 22

12

Connect a test lamp between the battery positive voltage circuit and the ground circuit of the ALC air compressor.

Does the test lamp illuminate?

Go to Step 15

Go to Step 21

13

Probe the ALC height sensor circuit of the automatic level control inflation time relay connector with a test lamp connected to a good ground.

Does the test lamp illuminate?

Go to Step 16

Go to Step 14

14

Probe the battery positive voltage circuit of the ALC inflation time relay connector with a test lamp connected to a good ground.

Does the test lamp illuminate?

Go to Step 25

Go to Step 17

15

Test the ALC compressor harness for a poor connection or an open. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs or Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 27

Go to Step 26

16

Repair the open in the ALC height sensor circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 27

--

17

Repair the open in the battery positive voltage circuit to the automatic level control inflation time relay. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 27

--

18

Repair the open in the ALC sensor ground circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 27

--

19

Repair the open in the ALC relay coil supply voltage circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 27

--

20

Repair the open in the accessory voltage circuit to the ALC relay. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 27

--

21

Repair the open in the ALC air compressor ground circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 27

--

22

Repair the open in the battery positive voltage circuit of the ALC air compressor. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 27

--

23

Replace the ALC sensor. Refer to Automatic Level Control Sensor Replacement .

Did you complete the replacement?

Go to Step 27

--

24

Replace the ALC air compressor relay.

Did you complete the replacement?

Go to Step 27

--

25

Replace the ALC inflation time relay.

Did you complete the replacement?

Go to Step 27

--

26

Replace the ALC air compressor. Refer to Air Compressor Replacement .

Did you complete the replacement?

Go to Step 27

--

27

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 3