Circuit Description
When the automatic level control (ALC) sensor detects an out of trim condition, the auto level control relay K19 energizes to provide B+ to the auto level control air compressor. The ALC sensor continuously monitors the controlling circuitry to determine if there is B+ 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 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
Check 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 Testing for Intermittent Conditions and Poor Connections in Wiring Systems. |
Test Description
The number(s) below refer to the step number(s) on the diagnostic table.
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Tests the ignition 1 voltage circuit of the auto level control relay K19.
-
Tests the control circuit of the auto level control relay K19.
-
Tests for an open in the relay coil.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Schematic Reference: Automatic Level Control Schematics | ||||
1 | Did you perform the Automatic Level Control (ALC) Diagnostic System Check? | -- | ||
Is the measured voltage within the specified value? | B+ | |||
3 | Repair the open, high resistance or short to ground in the ignition 1 voltage circuit of the auto level control relay K19. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | -- | |
Is the measured voltage near the specified value? | 12 V | |||
5 | Repair the open, high resistance, or short to ground in the control circuit of the auto level control relay K19. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | -- | |
Measure the resistance between the ignition 1 voltage circuit of the auto level control relay K19 and the control circuit of the auto level control relay K19 at the relay box. Is the measured resistance within the specified value? | 80 ohms-85 ohms | |||
7 | Replace the auto level control relay K19. Is the repair complete? | -- | -- | |
8 |
Important: After replacement calibrate the trim setting for the ALC sensor. Replace the ALC sensor. Refer to Automatic Level Control Sensor Replacement . Is the repair complete? | -- | -- | |
9 | Operate the system in order to verify the repair. Did you correct the condition? | -- | System OK | |
