Cummins ISL CM850 (2003-06) Fault Code: 691 PID: SPN: 1172 FMI: 3 Turbocharger Number 1 Compressor Inlet Temperature Sensor Circuit – Voltage Above Normal or Shorted to High Source. High signal voltage detected at the turbocharger compressor inlet air temperature circuit.

Cummins ISL CM850 (2003-06) Fault Code: 691 PID: SPN: 1172 FMI: 3 Turbocharger Number 1 Compressor Inlet Temperature Sensor Circuit – Voltage Above Normal or Shorted to High Source. High signal voltage detected at the turbocharger compressor inlet air temperature circuit.

The turbocharger inlet air temperature sensor shares return wires in the engine harness with other sensors. An open return can cause multiple fault codes to be active. Before troubleshooting Fault Code 691, check for multiple fault codes. An extension harness between the main engine harness and the turbocharger compressor inlet temperature sensor may be used depending on the turbocharger arrangement.

Possible causes:

1)Open return circuit in the harness, connectors, or sensor
2)Open signal circuit or short circuit to a voltage source
3)Failed sensor.

Possible repairs:

1)Replace the turbocharger compressor inlet air temperature sensor.
2)The removal and installation of the connector may correct the fault.
3)Replace the ECM.
4)Replace the engine harness.