Cummins ISX CM870 (2003-06) Fault Code: 691 PID: S151 SPN: 1172 FMI: 3/3 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.

Beginning with ESN 14039654, the temperature sensor return circuit was separated from the pressure sensor return circuit. For ESNs prior to this and with engine wiring harness Part Number 3682854, see the Common Pressure/Temperature Sensor Return Circuit above. For this ESN and greater or for any other engine wiring harness part number, see the Separate Pressure/Temperature Sensor Return Circuit above.

The turbocharger compressor 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.

Possible causes:

1)Open return circuit in the harness, connectors, sensor, or ECM
2)Open signal circuit or shorted to a voltage source.

Possible repairs:

1)Replace the turbocharger compressor intake air temperature sensor.
2)Replace the ECM.
3)Repair or replace the engine harness or sensor extension harness.