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For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2005 🢒 DeVille 🢒 Vehicle Control Systems 🢒 Vehicle DTC Information 🢒 Rear of Vehicle Low

Rear of Vehicle Low w/F45

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 in Vehicle DTC Information

2
  1. Turn ON the ignition, with the engine OFF.
  2. Listen for the automatic level control (ALC) air compressor to activate.

Does the air compressor come on within 30 seconds?

Go to Step 9

Go to Step 3

3
  1. Turn OFF the ignition.
  2. Disconnect the ALC connector from the ALC air compressor assembly.
  3. Disconnect connector C2 from the Electronic Suspension Control Module.
  4. Turn ON the ignition, with the engine OFF.
  5. Connect ALC relay control circuit to ground.
  6. Measure the voltage between the ALC compressor motor control circuit of the ALC air compressor connector and ground.

Does the voltmeter display a voltage greater than 10 volts?

Go to Step 4

Go to Step 7

4
  1. Remove the jumper wire from the ALC relay control circuit.
  2. Turn OFF the ignition.
  3. Check for continuity between ALC compressor ground circuit of the ALC air compressor connector and ground.

Is there continuity?

Go to Step 6

Go to Step 5

5
  1. Turn OFF the ignition.
  2. Repair the open circuit in the ALC air compressor ground circuit.

Is the repair complete?

Go to Step 14

--

6

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

Is the repair complete?

Go to Step 12

--

7
  1. Remove the jumper wire from ALC relay control circuit.
  2. Turn OFF the ignition.
  3. Check for the following:
    4. • Blown (open) ELC fuse
    • Bad electronic level control (ELC) relay
    • Open circuit in ALC air compressor control circuit
    • Open circuit in ELC relay control circuit

Was a problem found?

Go to Step 8

--

8

Important: A blown fuse may indicate:

    • No compressor head pressure relief
    • A faulty air compressor
    • A short to ground in the exhaust solenoid supply circuit

Repair the shorted circuit condition or replace the fuse.

Is the repair complete?

Go to Step 14

--

9

Inspect the left and right rear position sensors for damage and disconnected links.

Are any damaged sensors or disconnected links present?

Go to Step 13

Go to Step 10

10

Perform the ALC System Leak Test.

Is a leak present?

Go to Step 11

Go to Step 12

11

Repair the leak in the ALC System.

Is the repair complete?

Go to Step 14

--

12
  1. Turn OFF the ignition.
  2. Connect the scan tool.
  3. Turn ON the ignition, with engine OFF.
  4. Perform the ALC Trim Height Adjustment.

Has the ALC trim height adjustment been completed?

Go to Step 14

--

13

Replace the damaged rear position sensor or reconnect the link. Refer to Automatic Level Control Sensor Replacement .

Is the replacement complete?

Go to Step 14

--

14

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 1

Rear of Vehicle Low w/o F45

Step

Action

Value(s)

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 in Vehicle DTC Information

2
  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, command the ALC relay ON and OFF.

Does the ALC relay turn ON and OFF with each command?

--

Go to Step 8

Go to Step 3

3
  1. Turn OFF the ignition.
  2. Disconnect the automatic level control (ALC) relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the coil side feed circuit of the ALC relay with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

--

Go to Step 4

Go to Step 15

4
  1. Connect a test lamp between the control circuit of the ALC relay and the coil side feed circuit of the ALC relay.
  2. With a scan tool, command the ALC relay ON and OFF .

Does the test lamp turn ON and OFF with each command?

--

Go to Step 11

Go to Step 5

5

Does the test lamp remain illuminated with each command?

--

Go to Step 7

Go to Step 6

6

Test the control circuit of the ALC relay for a short to voltage or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 19

Go to Step 13

7

Test the control circuit of the ALC for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 19

Go to Step 13

8
  1. Turn OFF the ignition.
  2. Disconnect the ALC compressor motor.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the ALC compressor motor battery positive feed circuit with a test lamp connected to a good ground.
  5. With a scan tool, command the ALC relay ON.

Did the test lamp illuminate?

--

Go to Step 9

Go to Step 13

9
  1. Turn OFF the ignition.
  2. Disconnect the negative battery cable.
  3. Measure the resistance of the ALC compressor ground circuit to a good ground.

Is the resistance lower than the specified value?

5 ohms

Go to Step 12

Go to Step 14

10

Test the ALC compressor motor battery positive feed circuit for an open. Refer to Circuit Testing in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 19

Go to Step 11

11

Inspect for poor connections at the ALC relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 19

Go to Step 16

12

Inspect for poor connections at the ALC compressor assembly. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 19

Go to Step 17

13

Inspect for poor connections at the harness connector of the rear integration module (RIM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 19

Go to Step 18

14

Repair the high resistance/open ALC compressor ground circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 19

--

15

Repair the coil side feed circuit of the ALC relay Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 19

--

16

Replace the ALC relay .

Did you complete the replacement?

--

Go to Step 19

--

17

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

Did you complete the replacement?

--

Go to Step 19

--

18

Replace the RIM module. Refer to Rear Integration Body Control Module Replacement in Computer/Integrating Systems.

Did you complete the replacement?

--

Go to Step 19

--

19

Operate the system to verify the repair.

Does the system operate normally?

--

System OK

Go to Step 2