Circuit DescriptionThe ECM supplies 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 LocationThe intake manifold 1 pressure/temperature sensor is located in the air intake horn.

Conditions for Running the DiagnosticsThis diagnostic runs continuously when the engine is operating at idle.

Conditions for Setting the Fault CodesThe intake manifold temperature was less than 20°C [68°F] while the engine was idleing for an extended period of time.

Action Taken When the Fault Code is ActiveThe ECM illuminates the amber CHECK ENGINE lamp immediately when the diagnostic runs and fails.Conditions for Clearing the Fault CodeTo 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.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 TalkThe EGR valve was closed because the engine was idling with cold intake manifold temperatures for an extended period of time.

Possible Cause:1) Intake Manifold Temperature sensor failure2) ECM calibration