Circuit DescriptionThe ambient air temperature sensor is a variable resistor sensor and is used to measure the temperature of the ambient air. The engine control module (ECM) uses this temperature reading to optimize engine performance, and determine if heating of the SCR system is required. The engine control module (ECM) supplies 5 volts to the ambient air temperature signal circuit. The ECM monitors the change in voltage caused by changes in the resistance of the sensor to determine the ambient air temperature.

Component LocationThe mounting location for the ambient air temperature sensor is OEM dependent. Refer to the appropriate OEM service manual.

Conditions for Running the DiagnosticsThis diagnostic consists of two parts. The first part runs when the keyswitch is turned ON and before engine speed is detected. The ECM must not see a key cycle for a period of 8 hours before this part of the diagnostic will run.

The second part runs continuously while the engine is running.Conditions for Setting the Fault CodesThe Engine Control Module (ECM) detected the ambient air temperature reading was higher or lower than the other temperature sensors on the engine after an extended period of engine off time, or the ambient air temperature was reading was too high or too low for the engine operating conditions.

Action Taken When the Fault Code is ActiveThe 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 ambient air temperature reading is used.Active and stationary regeneration of the diesel particulate filter will be disabled.Engine torque will be reduced if the engine is operated for an extended period of time with this fault active.Conditions for Clearing the Fault CodeTo validate the repair, perform a key cycle, start the engine and let it idle for 1 minute.If the fault code does not go inactive, it may be necessary to perform a 8 hour cold soak with the key OFF, then turn the keyswitch to the ON position so that the key ON portion of the diagnostic will run.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 TalkPossible causes of this fault code include:

Stuck in-range ambient air temperature sensorHigh resistance in the ambient air temperature sensor signal or return linesECM malfunction.Reference the appropriate OEM wiring diagram when troubleshooting circuits that utilize wiring supplied by the OEM.

Possible Cause:1) OEM harness2) ECM failure