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:

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

Possible repairs:

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