GM Service Manual Online
For 1990-2009 cars only

Step

Action

Value(s)

Yes

No

1

Did you review the automatic level control suspension system operation and perform the necessary inspections?

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Go to Step 2

Go to Symptoms

2

Verify that the ALC compressor motor does not activate.

Does the ALC system operate normally?

--

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

Go to Step 3

3

Inspect the LD LEV Fuse for an open.

Is the fuse open?

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Go to Step 4

Go to Step 5

4

Repair the short to ground in CKT 1840 (ORN). Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Replace the LD LEV Fuse.

Is the repair complete?

--

Go to Step 32

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5

  1. Ensure that the ALC inflator air switch is in the OFF position.
  2. Turn the ignition switch to the LOCK position.
  3. Disconnect the ALC Air Compressor connector.
  4. Turn the ignition switch to the RUN position. Do not start the engine.
  5. Using a DMM, test for voltage present at the ALC Air Compressor cavity E.

Is voltage present?

9-16V

Go to Step 7

Go to Step 6

6

Repair the open or high resistance in CKT 1840 (ORN). Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Step 32

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7

Inspect the IGN E Fuse for an open.

Is the fuse open?

--

Go to Step 8

Go to Step 9

8

Repair the short to ground in CKT 639 (PNK). Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Step 32

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9

With the ignition switch in the RUN position, test for voltage present at the ALC Air Compressor cavity A.

Is voltage present?

9-16V

Go to Step 11

Go to Step 10

10

Repair the open or high resistance in CKT 639 (PNK). Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Step 32

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11

Using a test lamp, connect from the ALC Air Compressor connector cavity E to cavity G.

Did the test lamp light?

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Go to Step 13

Go to Step 12

12

Repair the open or high resistance in CKT 1350 (BLK) or G470. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Step 32

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13

  1. Turn the ignition switch to the LOCK position.
  2. Reconnect the ALC Air Compressor
  3. Disconnect the ALC sensor.
  4. Turn the ignition switch to the RUN position. Do not start the engine.
  5. Test CKT 639 (PNK) at terminal D for voltage.

Is voltage present?

9-16V

Go to Step 15

Go to Step 14

14

Repair the open or high resistance in CKT 639 (PNK) between the ALC sensor and S473. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Step 32

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15

Using a test lamp, connect from the ALC sensor connector cavity D to cavity A.

Did the test lamp light?

--

Go to Step 17

Go to Step 16

16

Repair the open or high resistance in CKT 1350 cavity A and S471. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Step 32

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17

Test CKT 1298 (LT BLU) at terminal C for an open circuit.

Is an open present in CKT 1298 (LT BLU)?

--

Go to Step 27

Go to Step 18

18

Connect a fused jumper wire from terminal B, CKT 321 (YEL) to ground.

Does the pump start and run?

--

Go to Step 19

Go to Step 20

19

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

Is the replacement complete?

--

Go to Step 32

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20

Connect a fused jumper wire from the load leveling pump connector terminal D at CKT 321 (YEL) to ground.

Does the pump start and run?

--

Go to Step 21

Go to Step 22

21

Repair the open in CKT 321 (YEL) between the ALC Air Compressor and the ALC sensor.

Is the repair complete?

--

Go to Step 32

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22

  1. Turn the ignition switch to the OFF position.
  2. Remove the ALC Air Compressor.
  3. Inspect following circuits for opens:
  4. • CKT 321 (YEL) to the relay
    • CKT 1840 (ORN) to the relay
    • CKT 1350 (BLK) to the motor bracket

Did you find an open circuit?

--

Go to Step 23

Go to Step 24

23

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

Is the repair complete?

--

Go to Step 32

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24

  1. Reconnect the ALC Air Comprerssor connectors.
  2. Connect a test lamp at the ALC Air Compressor relay for the BLK/LT GRN wire.
  3. Turn the ignition switch to the RUN position. Do not start the engine.
  4. Wait 40 seconds.

Does the test lamp illuminate?

--

Go to Step 26

Go to Step 25

25

Replace the ALC Air Compressor relay. Refer to Air Compressor Relay Replacement .

Is the replacement complete?

--

Go to Step 32

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26

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

Is the replacement complete?

--

Go to Step 32

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27

  1. Access the ALC timer relay.
  2. Test CKT 1298 (LT BLU) at terminal B of the ALC timer relay for an open circuit.

Is an open present in CKT 1298 (LT BLU)?

--

Go to Step 28

Go to Step 29

28

Repair the open in CKT 1298 (LT BLU) between the ALC timer relay and the ALC sensor. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Step 32

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29

Test CKT 1840 (ORN) at terminal D for an open circuit.

Is an open present in CKT 1840 (ORN)?

--

Go to Step 30

Go to Step 31

30

Repair the open in CKT 1840 (ORN). Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Step 32

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31

Replace the ALC timer relay. Refer to Automatic Level Control Relay Replacement .

Is the replacement complete?

--

Go to Step 32

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32

Operate the system in order to verify the repair.

Did you correct the condition?

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System OK

Go to Step 3