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SPN 1172 - FMI 3 (Fault Code 691)

SPN1172 FMI3 (Turbocharger 1 Compressor Inlet Temperature Sensor Circuit - Voltage Above Normal or Shorted to High Source)
Fault Code 691
ISC and ISL with CM2150 - Turbocharger Compressor Inlet Temperature Sensor Circuit

CODES:
Fault Code: 691
PID(P), SID(S): P351
SPN: 1172
FMI: 3/3
Lamp: AMBER
SRT:
ISB with CM2150 - Ambient Air Temperature Sensor Circuit

REASON: Turbocharger 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.

EFFECT: Engine power derate.

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

Component Location:
The ISB with CM2150 uses a combination ambient air temperature/pressure sensor located in the OEM intake air plumbing rather than a turbocharger compressor inlet temperature sensor.

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

Conditions for Setting the Fault Codes:
The ECM detects that the compressor inlet temperature signal voltage is greater than 4.8-VDC for more than 1 second.

Action Taken When the Fault Code is Active:
• The ECM illuminates the amber CHECK ENGINE light immediately when the diagnostic runs and fails.
• A default value for the compressor inlet temperature reading is used.

Conditions for Clearing the Fault Code:
The ECM will turn off the amber CHECK ENGINE light immediately after the diagnostic runs and passes.

Shop Talk:
Verify the electronic control module (ECM) calibration is correct. Check the calibration revision history found on QuickServe™ Online for applicable fixes to the calibration stored in the ECM. If necessary, calibrate the ECM.

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 can be used depending on the turbocharger arrangement.

On ISB with CM2150 engines, an extension harness between the main harness and the ambient air temperature/pressure sensor is always used.

Possible causes of this fault code:
• Open return circuit in the harness, connectors, or sensor
• Open signal circuit or short circuit to a voltage source
• Damaged sensor.


Read More:
SPN 98 - FMI 0 (Fault Code 688)
SPN 103 - FMI 18 (Fault Code 687)








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