Cummins ISB4.5 CM2150 Fault Code: 527 PID: SPN: 702 FMI: 3 Auxiliary Input/Output 2 Circuit – Voltage Above Normal or Shorted to High Source.

Posted by PerDiezel Solutions on January 20, 2026

Circuit Description
The ECM provides a signal to the original equipment manufacturer (OEM) output control circuit to turn the OEM supplied accessory on and off. The OEM output control circuit varies by OEM. Certain OEMs can use a circuit return that is wired to the ECM or goes to the engine block or chassis ground.

Component Location
The output control circuit driver is an OEM device and the location of the circuit driver is dependant upon the OEM. Refer to the OEM troubleshooting and repair manual.

Shop Talk
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 0-VDC. If it detects a high voltage, this fault is recorded. If Fault Code 527 is still active after completing the following troubleshooting steps, consult the OEM service manual for procedures to check the OEM output device for an open circuit or short to ground.

Possible Causes
-Open circuit in the engine harness or OEM output control solenoid
-Short circuit to voltage source in the OEM harness
-Damaged ECM.

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WARNING!