Reason:
Intake Manifold 1 Temperature Sensor Circuit – Voltage Above Normal or Shorted to High Source. High signal voltage detected at intake manifold air temperature circuit.

Effect:
Fan will stay ON if controlled by the engine control module (ECM).

Circuit Description:
The Engine Control Module (ECM) provides 5 volts to the intake manifold temperature signal circuit, and monitors the change in voltage caused by changes in the resistance of the sensor to determine the intake manifold temperature. When the intake air is cold, the sensor (or thermistor) resistance is high. The ECM signal voltage only pulls down a small amount through the sensor to a ground. Therefore, the ECM senses a high signal voltage or low temperature. When the intake air is warm, the sensor resistance is low. The signal voltage pulls down a large amount. Therefore, the ECM senses a low signal voltage, or a high temperature.

Component Location:
The intake manifold 1 pressure/temperature sensor is located in the air intake horn.

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 intake manifold temperature signal voltage was out of range high.

Action Taken When the Fault Code is Active:
1) The ECM illuminates the amber CHECK ENGINE lamp and/or the Malfunction Indicator Lamp (MIL) immediately when the diagnostic runs and fails.
2) A default value is used for the intake manifold temperature reading.
3) Diesel exhaust fluid injection into the aftertreatment system is disabled.
4) Active and stationary regeneration of the diesel particulate filter will be disabled.
5) Exhaust Gas Recirculation (EGR) valve operation will be disabled.
6) 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 Code:
1) To validate the repair, perform a key cycle, start the engine and let it idle for 1 minute.
2) The fault code status displayed by INSITE™ electronic service tool will change to INACTIVE immediately after the diagnostic runs and passes.
3) The ECM will turn off the amber CHECK ENGINE lamp immediately after the diagnostic runs and passes.
4) 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.
5) 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 intake manifold air temperature sensor shares return wires in the engine harness with other sensors. Opens and shorts in the engine harness can cause multiple fault codes to be active. Check active fault codes with multiple counts first.

Possible Causes:
1) Open return circuit in the harness, connectors, or sensor
2) Open signal circuit or shorted to voltage source.
3) Malfunctioning intake manifold pressure/temperature sensor