GM Service Manual Online
For 1990-2009 cars only

Step

Action

Value(s)

Yes

No

1

Did you review the Automatic Level Control (ALC) System Operation?

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Go to Step 2

Go to Automatic Level Control System Operation

2

Important: The vehicle must be raised on a drive on hoist.

  1. Raise and support the vehicle.
  2. Disconnect the ALC position sensor harness connector.
  3. Using a test lamp connected to a good ground, probe the position sensor harness connector battery positive voltage terminal.

Does the test lamp illuminate?

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Go to Step 3

Go to Step 12

3

Connect a test lamp between the position sensor harness connector positive battery voltage terminal and the position sensor harness connector ground terminal.

Does the test lamp illuminate?

--

Go to Step 4

Go to Step 13

4

Using a 3 amp fused jumper wire, jumper the position sensor harness connector exhaust solenoid control circuit to a good ground.

Did the exhaust solenoid click?

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Go to Step 5

Go to Step 8

5

Did the vehicle lower?

--

Go to Step 6

Go to Step 10

6

Check the ALC position sensor adjustment. Refer to Automatic Level Control Sensor Adjustment .

Is the adjustment OK?

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Go to Step 14

Go to Step 7

7

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

Did you complete the adjustment?

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Go to Step 20

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8

Test the ALC exhaust solenoid feed circuit for a open circuit or a short to ground. Refer to Circuit Testing and Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Did you find and correct the condition?

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Go to Step 20

Go to Step 9

9

Test the ALC exhaust solenoid control circuit for a open circuit or a short to ground. Refer to Circuit Testing .

Did you find and correct the condition?

--

Go to Step 20

Go to Step 15

10

Disconnect the air tube assembly from the drier.

Did the vehicle lower?

--

Go to Step 15

Go to Step 11

11

Disconnect the air tube assembly from the shocks.

Did the vehicle lower?

--

Go to Step 16

Go to Step 17

12

Repair open circuit or short to ground on the position sensor positive battery circuit.

Did you complete the repair?

--

Go to Step 20

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13

Repair open circuit or short to voltage on the position sensor ground circuit.

Did you complete the repair?

--

Go to Step 20

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14

Inspect for poor connections / terminal tension at the harness connector for the ALC position sensor.

Did you find and correct the condition?

--

Go to Step 20

Go to Step 18

15

Inspect for poor connections / terminal tension at the harness connector for the ALC exhaust solenoid.

Did you find and correct the condition?

--

Go to Step 20

Go to Step 19

16

Replace the air tube assembly. Refer to Automatic Level Control Air Compressor Head Replacement .

Did you complete the replacement?

--

Go to Step 20

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17

Replace the shock that did not lower.

Did you complete the replacement?

--

Go to Step 20

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18

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

Did you complete the replacement

--

Go to Step 20

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19

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

Did you complete the replacement?

--

Go to Step 20

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20

Operate the vehicle within the conditions for enabling the automatic level control.

Does the ALC operate properly?

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System OK

Go to Step 2