Circuit DescriptionThe intake air heater improves starting and white smoke control in cold ambient conditions.

The electronic control module (ECM) controls relays that switch power to the intake air heater. Air heaters on 12 volt systems will have two relays while 24 volt systems only require one relay.

Component LocationThe intake air heater is located at the air inlet connection to the intake manifold. The location of the intake air heater relays will vary by vehicle and engine configuration.

Conditions for Running the DiagnosticsThis diagnostic runs when the keyswitch is in the ON position and when the pulse width modulated (PWM) device is activated. In some cases, the diagnostic can also run at certain fixed intervals.

Conditions for Setting the Fault CodesThe intake air heater circuit PWM signal is not detected to be system voltage when the PWM signal is turned on.

Action Taken When the Fault Code is ActiveThe ECM illuminates the amber CHECK ENGINE light immediately when the diagnostic runs and fails.The intake air heater circuit will be disabled.Conditions for Clearing the Fault CodeTo validate the repair, 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 after the diagnostic runs and passes.For on-board diagnostic (OBD) engines, the ECM will turn off 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:

A shorted intake air heater relayIntake air heater relay supply wire shorted to ground.

Possible Cause:1) OEM harness2) ECM failure