Circuit Description
The automatic level control (ALC) sensor controls the exhaust solenoid 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 sensor detects a feedback voltage less than the preset threshold during an exhaust valve OFF state.
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 poor connection at the ALC sensor |
| Inspect the harness connectors for backed out terminals, improper mating, improperly formed or damaged terminals, and poor terminal to wire connections. |
| • | 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.
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This step tests for an open or short to ground in the battery positive voltage circuit of the auto level control air compressor.
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This step tests for an open or short to ground in the exhaust solenoid control circuit of the auto level control air compressor.
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This step tests for an internal open or short to ground in the exhaust solenoid.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Automatic Level Control (ALC) System Check? | -- | Go to Step 2 | |
Is the voltage near the specified value? | 12 V | Go to Step 4 | Go to Step 3 | |
3 | Repair an open, high resistance, or a short to ground in the battery positive voltage circuit of the auto level control air compressor. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | Go to Step 10 | -- |
Is the voltage near the specified value? | 12 V | Go to Step 6 | Go to Step 5 | |
5 | Repair an open, high resistance, or a short to ground in the compressor exhaust control circuit. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | Go to Step 10 | -- |
Measure the resistance between terminal C and terminal A of the auto level control air compressor. Is the resistance reading within the specified range? | 25 ohms-35 ohms | Go to Step 7 | Go to Step 8 | |
7 |
Does the LEVELING indicator lamp flash? | -- | Go to Step 9 | Go to Step 10 |
8 | Replace the complete air compressor head. Refer to Automatic Level Control Air Compressor Head Replacement . Is the repair complete? | -- | Go to Step 10 | -- |
9 | Replace the ALC sensor. Refer to Automatic Level Control Sensor Replacement . Is the repair complete? | -- | Go to Step 10 | -- |
10 | Operate the system in order to verify the repair. Did you correct the condition? | -- | System OK | Go to Step 2 |
