For 1990-2009 cars

### Circuit Description

When the automatic level control sensor detects an out of trim condition, the rear suspension leveling air compressor relay K19 energizes in order to provide B+ to the rear suspension leveling air compressor. The automatic level control sensor continuously monitors the controlling circuitry in order to determine if B+ is present for a compress sequence or an air replenishment cycle (ARC).

### Conditions for Setting the DTC

The sensor detects that the relay output is not pulled up to B+ when the sensor output is deactivated and the ignition signal is active.

### Action Taken When the DTC Sets

• | The sensor flashes the LEVELING indicator lamp.

• | The sensor's discrete low side output drive for the relay is disabled.

• | The compressor is inoperative.

• | The sensor continuously attempts to recover from the fault.

• | DTC 04 is stored as a history code at the end of the ignition cycle.

### Conditions for Clearing the DTC

• | A current DTC becomes a history DTC when conditions for the fault are no longer present and the ignition cycles from OFF to ON.

• | A history DTC will clear after 20 ignition cycles.

• | Use a scan tool in order to clear this DTC.

### Diagnostic Aids

Inspect for the following conditions if a history or intermittent DTC is indicated:

• | A damaged wiring harness

| Inspect the wiring harness for damage. If the wiring harness appears to be in good condition, observe the display on the DMM while moving the connectors and wiring harnesses related to the circuits. A change in the DMM display during this test will indicate the location of the fault.

• | For additional information, refer to Intermittents and Poor Connections Diagnosis in Wiring Systems.

### Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

1. This step checks the condition of circuit X470.

2. This step checks the condition of circuit B25 and circuit B56.

3. This step checks for an open in the internal coil of the relay.

#### DTC 04 Compressor Relay Short to Ground/Open Circuit

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Automatic Level Control (ALC) System Check performed? | -- | Go to Step 2 | Go to Automatic Level Control Suspension System Check
2 |

1. Disconnect the rear suspension leveling air compressor relay K19 form the relay box.
2. Turn the ignition switch to the ON position.
3. Use a DMM in order to measure the voltage between relay box terminal 3 and a good ground.

Is the measured voltage equal to the specified value?

B+

Go to Step 4

Go to Step 3

3 |

1. Locate an open, high resistance, or short to ground in circuit X470.
2. Repair the open, high resistance, or short to ground in circuit X470.

Is the repair complete?

--

Go to Step 9

--

4 |

1. Disconnect the ALC sensor connector.
2. Connect a fused jumper wire between terminal 3 and terminal 1 at the relay box.
3. Use the DMM in order to measure the voltage between terminal C of the ALC sensor connector and a known good ground.

Is the measured voltage equal to the specified value?

B+

Go to Step 6

Go to Step 5

5 |

1. Locate an open, high resistance, or short to ground in circuit B25 and/or circuit B56.
2. Repair the open, high resistance, or short to ground in circuit B25 and/or circuit B56.

Is the repair complete?

--

Go to Step 9

--

6 | Measure the resistance between terminal 3 and terminal 1 of the rear suspension leveling air compressor relay K19. Is the measured resistance within the specified range? | 80 ohms-85 ohms | Go to Step 8 | Go to Step 7
7 | Replace the rear suspension leveling air compressor relay K19. Is the replacement complete? | -- | Go to Step 9 | --
8 | Replace the ALC sensor. Refer to Automatic Level Control Sensor Replacement . Is the replacement complete? | -- | Go to Step 9 | --
9 |

1. Clear any DTCs.
2. Connect all of the connectors that were disconnected.
3. Reinstall all of the components that were removed.
4. Wait at least 5 minutes.
5. Turn the ignition switch to the ON position.

Is the LEVELING indicator lamp flashing?

--

Go to Step 1

System OK