Cummins ISB 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.

Posted by PerDiezel Solutions on January 18, 2026

Cummins ISB 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.

Cummins ISB CM850 (2003-06) Fault Code: 689 PID: 190 SPN: 190 FMI: 2 Engine Crankshaft Speed/Position – Data Erratic, Intermittent, or Incorrect. Loss of signal from crankshaft sensor.

Cummins ISB CM850 (2003-06) Fault Code: 688 PID: 98 SPN: 98 FMI: 0 Engine Oil Level ? Data Valid But Above Normal Operational Range ? Most Severe Level. High oil level has been detected by the oil level sensor.

Cummins ISB CM850 (2003-06) Fault Code: 687 (ISC) PID: 103 SPN: 103 FMI: 1 Turbocharger Number 1 Speed Low – Data Valid but Below Normal Operational Range – Moderately Severe Level. Low turbocharger speed detected by the ECM.

Cummins ISB CM850 (2003-06) Fault Code: 687 (ISB) PID: 103 SPN: 103 FMI: 18 Turbocharger number 1 speed low – warning level. Low turbocharger speed detected by the ECM.

Cummins ISB CM850 (2003-06) Fault Code: 649 PID: SID 153 SPN: 1378 FMI: 11 Change Lubricating Oil and Filter – Condition Exists. Change engine oil and filter.

Cummins ISB CM850 (2003-06) Fault Code: 599 PID: SID 25 SPN: 640 FMI: 14 Auxiliary Commanded Dual Output Shutdown – Special Instructions. The engine protection limit has been exceeded for the dual outputs calibrated limits

WARNING!