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DTC C1786: RTD Control Relay Malfunction

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). ESC controls the operation of the RTD relay by grounding the relay trigger wire on ESC connector C2 terminal C13 (Dark Blue). It then monitors the voltage on terminal D1 to determine if the supply circuits are functioning properly. DTC C1786 will be set when the ESC detects low voltage on terminal D1 (orange wire), while terminal C13 (Dark Blue) is being grounded to energize the RTD relay. ESC module will disable all 4 shock absorbers (giving a soft ride), send a request to IPC to display SERVICE RIDE CONTROL and SHOCKS INOPERATIVE messages, 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 C1787 or C1788 is stored. If DTC C1787 or C1788 is stored, go to appropriate DTC for diagnosis. See DIAGNOSTIC TROUBLE CODE (DTC) IDENTIFICATION  table under DIAGNOSIS & TESTING. If DTC C1787 or C1788 is not stored, go to next step.
  3. Check 10-amp RTD relay fuse (No. 7) located in underhood electrical center. If fuse is blown (open), go to step  6 . If fuse is okay, go to next step.
  4. Turn ignition off. Measure voltage between ground and RTD control module connector C2, terminal D13 (Orange wire). If voltage is more than 10 volts, go to step  10 . If voltage is less than 10 volts, go to next step.
  5. Turn ignition off. Disconnect RTD relay located in underhood electrical center. Measure voltage between ground and battery circuit of RTD relay connector. If voltage is more than 10 volts, go to step  8 . If voltage is less than 10 volts, go to step  9 .
  6. Turn ignition off. Disconnect RTD control module connector C2. Check for continuity between ground and RTD control module connector C2, terminal D1 (Orange wire). If continuity exists, go to step  8 . If continuity does not exist, go to next step.
  7. Check for short to ground in damper solenoid drive high circuits No. 1114 and No. 1118 (both Dark Blue/White wires), and No. 1116 and No. 1107 (both Light Blue wires). See WIRING DIAGRAMS  . After repairs, go to step  13 . If all wires (circuits) are okay, go to step  12 .
  8. Check for open in circuit No. 1040 (connector C2, terminal D1, Orange wire). After repairs, go to step  13 . If circuit is okay, go to step  11 .
  9. Locate and repair open in underhood electrical center or power feed to electrical center. After repairs, go to step  13 .
  10. Check RTD relay circuit for intermittent short to ground in Orange wire. Check for short to ground on any damper solenoid drive high circuit. See NOTES ON INTERMITTENTS  under DIAGNOSIS & TESTING. See WIRING DIAGRAMS  . After repairs, go to step  13 . If Orange wire and damper drive high circuits are okay, system is functioning properly.
  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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