P0540

CIRCUIT DESCRIPTION
The Engine Control Module (ECM) uses an Intake Air Heater (IAH) to warm the incoming air for proper cylinder combustion. The ECM grounds the control coil of the IAH relay to energize the heater during cold operation. If the ECM detects voltage on the IAH circuit when the relay is commanded OFF, or incorrect voltage when the relay is commanded ON, a Diagnostic Trouble Code (DTC) will set.

CONDITIONS FOR RUNNING THE DTC
^ The battery voltage is between 10-18 volts.
^ The Intake Air Temperature (IAT) is less than 23 °C (73 °F) with the engine running.

OR

^ The coolant temperature is less than 49 °C (121°F) with the ignition ON, engine OFF for more than 3 seconds.

CONDITIONS FOR SETTING THE DTC
The heater line voltage is more than 8.1 volts with the relay OFF.

OR

The heater line voltage is between 3.8-8.1 volts with the ignition OFF.

AND

The heater line voltage is less than 0.5 volts below battery voltage with the ignition ON.

OR

The heater line voltage is less than 3.8 volts with the relay OFF.

AND

The reference line voltage is low with the relay OFF.

ACTION TAKEN WHEN THE DTC SETS
^ The control module illuminates the Malfunction Indicator Lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
^ The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The control module turns OFF the Malfunction Indicator Lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
^ A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
^ A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
^ Use a scan tool in order to clear the MIL and the DTC.

TEST DESCRIPTION

Steps 1-10:

Steps 11-18:

The number below refers to the step number on the diagnostic table.
4. This step checks for battery voltage output from the IAH relay to the IAH.