Cummins ISB CM850 (2003-06) Fault Code: 529 PID: SID 51 SPN: 703 FMI: 3 Auxiliary Input/Output 3 Circuit – Voltage Above Normal, or Shorted to High Source. High signal voltage has been detected at the auxiliary input/output 3 circuit.

Posted by PerDiezel Solutions on January 18, 2026

The ECM monitors the voltage level on this circuit. When the ECM commands the OEM output signal low, it expects the voltage level to be approximately zero volts. If it detects a high voltage, this fault is recorded. If Fault Code 529 is still active after completing the following troubleshooting steps, consult the OEM service literature for procedures to check the OEM output device for an open circuit or short to ground.

Possible causes:

1)Open circuit in the engine harness or OEM output control solenoid
2)Short circuit to voltage source in the OEM harness
3)Failed ECM.

Possible repairs:

1)Replace the OEM output control solenoid.
2)Repair or replace the OEM harness.
4)Replace the ECM.
5)The removal and installation of the connector may corrected the problem.

Cummins ISB CM850 (2003-06) Fault Code: 528 PID: 93 SPN: 93 FMI: 2 Auxiliary Alternate Torque Validation Switch – Data Erratic, Intermittent, or Incorrect. An error has been detected in the alternate torque switch circuit.

Cummins ISB CM850 (2003-06) Fault Code: 527 PID: SID 154 SPN: 702 FMI: 3 Auxiliary Input/Output 2 Circuit Voltage Above Normal or Shorted to High Source. High signal voltage or open circuit has been detected at the auxiliary input and output 2 circuit.

Cummins ISB CM850 (2003-06) Fault Code: 523 PID: 89 SPN: 611 FMI: 2 Auxiliary Intermediate (PTO) Speed Switch Validation – Data Erratic, Intermittent, or Incorrect. The position of the intermediate speed control switch 1 does not match the position of the intermediate speed control validation switch.

Cummins ISB CM850 (2003-06) Fault Code: 499 PID: 98 SPN: 98 FMI: 4 Engine Oil Level Sensor Circuit – Voltage Below Normal or Shorted to Low Source. The engine oil level sensor has detected an internal failure.

Cummins ISB CM850 (2003-06) Fault Code: 498 PID: 98 SPN: 98 FMI: 3 Engine Oil Level Sensor Circuit – Voltage Above Normal or Shorted to High Source. The engine oil level sensor has detected an internal failure.

Cummins ISB CM850 (2003-06) Fault Code: 497 PID: SID 114 SPN: 1137 FMI: 2 Multiple Unit Synchronization Switch – Data Erratic, Intermittent, or Incorrect. Multi-Unit synchronous ON/OFF switch and Multi-Unit synchronous complimentary ON/OFF switch have different values in the ECM.

WARNING!