Cummins X15 CM2450 X124B (2018 & Newer) Fault Code: 691 PID: PID 351 SPN: 1172 FMI: 3 Turbocharger 1 Compressor Intake Temperature Circuit- Voltage Above Normal or Shorted to High Source

Circuit Description
The compressor intake air temperature sensor is a variable resistor sensor and is used to measure the temperature of the air entering the compressor intake of the turbocharger. The engine control module (ECM) supplies 5-VDC to the compressor intake temperature signal circuit. The ECM monitors the change in voltage caused by changes in the resistance of the sensor to determine the air temperature.

Component Location
The turbocharger compressor intake temperature sensor is located in the compressor inlet of the turbocharger.

Conditions for Running the Diagnostics
This diagnostic runs continuously when the keyswitch is in the ON position or when the engine is running.

Conditions for Setting the Fault Codes
The Engine Control Module (ECM) detected the compressor intake temperature signal voltage was out of range high.

Action Taken When the Fault Code is Active
The ECM illuminates the amber CHECK ENGINE lamp and/or the Malfunction Indicator Lamp (MIL) immediately when the diagnostic runs and fails.
A default value for the compressor intake temperature reading is used.
Conditions for Clearing the Fault Code
To validate the repair, perform a key cycle, start the engine and let it idle for 1 minute.
The fault code status displayed by INSITE™ electronic service tool will change to INACTIVE immediately after the diagnostic runs and passes.
The ECM will turn off the amber CHECK ENGINE lamp immediately after the diagnostic runs and passes.
For On-Board Diagnostics (OBD) engines, the ECM will extinguish the Malfunction Indicator Lamp (MIL) after three consecutive trips where the diagnostic runs and passes.
The Reset All Faults command in INSITE™ electronic service tool can be used to clear active and inactive faults, as well as extinguish the MIL for OBD applications.

Shop Talk
The turbocharger compressor intake 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 intake temperature sensor can be used depending on the turbocharger arrangement.

Possible causes of this fault code include:

Open return circuit in the harness, connectors, or sensor
Open signal circuit or short circuit to a voltage source
Damaged sensor.

Possible Cause:
1) ECM failure
2) Engine harness
3) OEM harness