C1738

CIRCUIT DESCRIPTION
The Automatic Level control (ALC) exhaust solenoid valve is controlled (switched ON or OFF) by the Continuously Variable Road Sensing Suspension (CVRSS) control module. The control module provides a low-side drive (switched to ground) whenever exhaust activity is required and during a head-relief sequence which occurs before each compressor start-up. This drive output from the CVRSS control module is continually monitored to determine if the voltage level agrees with the commanded state.

CONDITIONS FOR SETTING THE DTC
The Diagnostic Trouble Code (DTC) will set when the CVRSS control module measures a feedback voltage condition at pin C14 less than a preset threshold during an exhaust solenoid valve OFF-state. The DTC will turn history when the CVRSS control module no longer senses a low voltage condition at pin C14 when the exhaust solenoid valve is in an OFF-state.

ACTION TAKEN WHEN THE DTC SETS
^ ALL rear leveling activity for the remainder of the ignition cycle will be disabled.
^ The SERVICE RIDE CONTROL message will be displayed.

CONDITIONS FOR CLEARING THE MIL/DTC
^ Use the scan tool.
^ Use the On-Board diagnostic CLEAR RSS CODES feature.

DIAGNOSTIC AIDS
A temporary compressor overload (i.e., high head pressure during a cold start) may cause the Electronic Suspension Control Maxi circuit breaker to trip. This is one possible cause of DTC C1738. A DTC C1738 fault condition is detectable only when the exhaust solenoid valve output is commanded to the OFF-state, which occurs whenever exhaust activity is not required. The CVRSS control module expects to see a high voltage condition during the OFF-state. Only electrical problems with the exhaust solenoid valve are flagged. Pneumatic blockage problems do not set a DTC, but the CVRSS control module shuts off the exhaust function if no progress is made, or if excessive run time occurs. Recovery is not attempted until the ignition is cycled OFF and ON. Check for disconnected or damaged air lines. Replace or reconnect the air lines as needed.

TEST DESCRIPTION

Important:
^ Do not backprobe the sensors, actuators, or any sealed connectors.
^ When all the diagnostics and repairs are complete, clear the DTCs and verify the operation.

The number(s) below refer to the step number(s) on the diagnostic table.
1. This step checks to see if the Electronic Suspension Control circuit breaker is tripped.
2. This step checks for an open circuit condition in circuit 1340.
3. This step checks for an internal open circuit condition in the exhaust solenoid valve.
4. This step checks for a short circuit to ground condition in circuit 320.
5. This step checks for an open circuit condition in circuit 320.
6. This step checks for an internal short circuit condition in the exhaust solenoid valve.
7. This step checks for a short circuit to ground condition in circuits 1340 and 322.
8. This step checks for a short circuit to ground condition in the compressor assembly pigtail or internally to the compressor assembly.