C1787

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Circuit Description
Solenoid drive voltage is applied to the ESC module through the Real Time Dampening (RTD) relay circuit. The ESC then closes the relay's contacts in order to ground the circuit and provide each shock absorber solenoid with this supplied voltage through the solenoid supply circuitry. Each individual solenoid low side drive then controls the operation of the corresponding shock absorber. The ESC module monitors the RTD relay control/solenoid supply circuits for any malfunction conditions.

Conditions for Setting the DTC
- The ESC module detects low voltage (an open or a short to ground) on the RTD relay control CKT 1944.
- Detection for this DTC can only be accomplished during the OFF (relay not applied) state.

Action Taken When the DTC Sets
- Stores a DTC C1787 in the ESC memory.
- Commands 0% PWM duty cycle in order to disable all four solenoids.
- Sends a message to the IPC to display the SERVICE RIDE CONTROL and the SHOCKS INOPERATIVE messages.
- Sends a message to the PCM to limit the speed. The PCM then sends a massage to the IPC to display the MAXIMUM SPEED 129 km/h (80 mph) message.

Conditions for Clearing the DTC
- The ignition must be cycled before this DTC can change from current to history even if the malfunction is no longer present.
- The ESC module no longer detects low voltage (an open or a short to ground) on the RTD relay control CKT 1944 with the relay OFF.
- A history DTC will clear after 100 consecutive ignition cycles if the condition for the malfunction is no longer present.
- The IPC clearing DTCs feature.
- Using a scan tool.

Diagnostic Aids
The following conditions may cause an intermittent malfunction:
- An open or a short to ground on the RTD relay control CKT 1944.
- An open RTD relay coil or high resistance condition.
- An open RTD relay fuse #7.
- A short to ground on any shock absorber solenoid drive high circuit.
- The RTD relay may be installed in the underhood electrical center in two directions and still function properly. Refer to Electrical Center Identification for relay circuit location whenever diagnostic procedures are performed in the underhood electrical center.
- The RTD relay provides supply voltage to all four shock absorber solenoids. Therefore, multiple shock absorber solenoid open or short to ground DTCs may also be stored along with a DTC C178 6. Diagnose a DTC C1786 first before attempting to diagnose a DTC C1787 or the multiple shock absorber solenoid DTCs.


Test Description
The numbers below refer to the step numbers on the diagnostic table:
2. This step checks if a DTC C1786 is stored in the ESC module's memory. A DTC C1786 must be diagnosed first before diagnosing a DTC C1787.
3. This step checks the underhood electrical center supply voltage.
4. This step checks for a short to ground on the RTD relay control CKT 1944.
5. This step measures the resistance of the RTD relay coil.
6. This step checks for an open on the RTD relay control CKT 1944.
7. This step checks for an intermittent malfunction and requests a thorough inspection of the related RTD relay circuit wiring and connectors.