Circuit Description
The automatic level control (ALC) sensor controls the exhaust valve. The ALC sensor provides a low side drive (switched to ground) whenever exhaust activity is required and during a "head-relief" sequence. A "head-relief" sequence occurs before each compressor start up. This drive output from the sensor is continually monitored in order to determine if the voltage level agrees with the commanded state.
Conditions for Setting the DTC
The ALC sensor detects that the exhaust solenoid valve output is not pulling down to ground when the sensor output is activated.
Action Taken When the DTC Sets
| • | The LEVELING indicator lamp flashes. |
| • | The sensor's discrete low side output drive for the valve is disabled. |
| • | The sensor continuously attempts to recover from the fault. |
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. |
| • | Perform the system leak test. Refer to Automatic Level Control System Operation Check . |
Test Description
The number(s) below refer to the step number(s) on the diagnostic table.
-
This step tests for a short to voltage in the control circuit of the exhaust solenoid valve in the air compressor.
-
This step tests for an internal short in the exhaust solenoid valve.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Automatic Level Control (ALC) System Check? | -- | Go to Step 2 | |
Does the voltage measure greater than the specified value? | 0.1 V | Go to Step 3 | Go to Step 4 | |
3 | Repair a short to voltage in the control circuit of the exhaust solenoid valve. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | Go to Step 8 | -- |
Measure the resistance between terminal C and terminal A of the auto level control air compressor at the air compressor. Is the resistance reading within the specified range? | 25 ohms-35 ohms | Go to Step 5 | Go to Step 7 | |
5 |
Is the LEVELING indicator lamp flashing? | -- | Go to Step 6 | Go to Step 8 |
6 | Replace the ALC sensor. Refer to Automatic Level Control Sensor Replacement . Is the repair complete? | -- | Go to Step 8 | -- |
7 | Replace the air compressor head. Refer to Automatic Level Control Air Compressor Head Replacement . Is the repair complete? | -- | Go to Step 8 | -- |
8 | Operate the system in order to verify the repair. Did you correct the condition? | -- | System OK | Go to Step 2 |
