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DTC C1787: RTD Relay Control Circuit (Open Or Short To Ground)

The ESC module gets supply voltage for all of the shock absorber solenoids, from the Real Time Damping (RTD) relay on ESC connector C2 terminal D1 (orange). The ESC controls the operation of the RTD relay by grounding the relay trigger wire on ESC connector C2 terminal C13 (Dark Blue). The ESC monitors the voltage on the relay control circuit on ESC terminal C13. If the voltage on C13 goes low (open circuit, short to ground, blown RTD fuse) while the ESC is not triggering the relay on that circuit, DTC C1787 will be set. The ESC will send a request to the IPC to display SERVICE RIDE CONTROL and SHOCKS INOPERATIVE messages, stop controlling the shock absorbers (giving a soft ride), and send a message to the PCM to limit vehicle speed to 80 MPH.

  1. Perform RTD diagnostic system check. See RTD DIAGNOSTIC SYSTEM CHECK  under DIAGNOSIS & TESTING. After performing RTD diagnostic system check, go to next step.
  2. Using scan tool, check if DTC C1786 is stored. If DTC C1786 is stored, go to appropriate DTC for diagnosis. See DIAGNOSTIC TROUBLE CODE (DTC) IDENTIFICATION  table under DIAGNOSIS & TESTING. If DTC C1786 is not stored, go to next step.
  3. Turn ignition off. Disconnect RTD relay located in underhood electrical center. Turn ignition on. Measure voltage between ground and battery circuit of RTD relay connector. If voltage is more than 10 volts, go to next step. If voltage is less than 10 volts, go to step  10 .
  4. Turn ignition off. Disconnect RTD control module connector C2. Check continuity between ground and RTD control module connector C2, terminal C13 (Dark Blue wire). If continuity exists, go to step  8 . If continuity does not exist, go to next step.
  5. Measure resistance of RTD relay coil between terminals No. 1 and 2 (or terminals No. 85 and 86). If resistance is 75-105 ohms, go to next step. If resistance is not 75-105 ohms, go to step  11 .
  6. Turn ignition off. Reconnect RTD relay. Measure voltage between ground and RTD control module connector C2, terminal C13 (Dark Blue wire). If voltage is more than 10 volts, go to next step. If voltage is less than 10 volts, go to step  9 .
  7. Check RTD relay circuit No. 641 (Dark Blue wire) for intermittent operation. See NOTES ON INTERMITTENTS  under DIAGNOSIS & TESTING. See WIRING DIAGRAMS  . After repairs, go to step  13 . If circuit is okay, go to step  12 .
  8. Locate and repair short to ground in underhood electrical center or circuit No. 641 (Dark Blue wire) between underhood electrical center and RTD control module connector C2, terminal C13. See WIRING DIAGRAMS  . After repairs, go to step  13 .
  9. Locate and repair open in circuit No. 1040 (Orange wire) between underhood electrical center and RTD control module connector C2, terminal D1. See WIRING DIAGRAMS  . After repairs, go to step  13 .
  10. Locate and repair open in underhood electrical center, 10-amp RTD fuse (fuse No. 7) or power feed to underhood electrical center. After repairs, go to step  13 .
  11. Replace RTD relay. After repairs, go to step  13 .
  12. Replace RTD control module. See RTD CONTROL MODULE  under REMOVAL & INSTALLATION. After repairs, go to next step.
  13. Turn ignition off. Reinstall/reconnect all components/connectors. Using scan tool, clear all DTCs.
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