Circuit Description
The automatic level control (ALC) sensor monitors the trim height of the rear of the vehicle. The ALC sensor compares the trim height of the vehicle with the desired trim height programmed in the ALC sensor memory. The ALC sensor energizes the exhaust solenoid valve to exhaust the air in the system when the vehicle is higher than the desired trim height.
Excessive exhaust solenoid valve activity is generally due to the presence of pneumatic line blockages or unloaded vehicle conditions.
Conditions for Setting the DTC
If the exhaust solenoid valve is active for more than 5 minutes and the rear of the vehicle remains above a trim position.
Action Taken When the DTC Sets
| • | All compressor exhaust activity is disabled. |
| • | The LEVELING indicator lamp flashes. |
Conditions for Clearing the DTC
| • | A current DTC becomes history 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. |
| • | Using a scan tool. |
Diagnostic Aids
Inspect for misrouted tubing or evidence of being pinched.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step inspects the ALC sensor actuating arm and link rod for damage.
-
Tests the operation of the exhaust solenoid valve.
-
Checks the exhaust operation of the ALC system.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Schematic Reference: Automatic Level Control Schematics | ||||
1 | Did you perform the Automatic Level Control (ALC) Diagnostic System Check? | -- | Go to Step 2 | |
Inspect the automatic level control (ALC) sensor actuating arm and link rod for abnormalities. Were any abnormalities found? | -- | Go to Step 5 | Go to Step 3 | |
Does the exhaust solenoid valve click? | -- | Go to Step 4 | Go to Step 6 | |
Is air exhausting from the air compressor air filter? | -- | Go to Diagnostic Aids | Go to Step 7 | |
5 |
Important: After replacement calibrate the trim setting for the ALC sensor.
Did you complete the replacement? | -- | Go to Step 8 | -- |
6 | Inspect for poor connections at the ALC sensor. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 8 | Go to Step 5 |
7 | Inspect the air filter and all tubing for blockage. Did you find and correct the condition? | -- | Go to Step 8 | Go to Step 9 |
8 | Operate the system in order to verify the repair. Did you find and correct the condition? | -- | System OK | Go to Step 3 |
9 | Replace the auto level control air compressor. Refer to Air Compressor Replacement . Did you complete the replacement? | -- | Go to Step 8 | -- |
