The intake air heater (IAH) is located in the air inlet tube and is used to warm the incoming air to aid in starting the engine and for proper cylinder combustion. The glow plug control module (GPCM) will command the IAH on when the engine coolant temperature is below 40°C (104°F). Power to the IAH is supplied by the battery positive voltage circuit. The IAH is connected to the GPCM by the following circuits. If there is a fault on any of these circuits a DTC will set.

One or more of the following conditions must be met:

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Electrical Information Reference

Scan Tool Reference

Important: If you cannot duplicate the condition, operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

With the ignition ON, observe that the following scan tool parameters are OK:

1. With the ignition ON, observe that the following scan tool parameters are OK:

•	The IA Heater overtemp parameter

•	The IA Heater overvoltage parameter

•	The IA Heater undervoltage parameter

•	The IA Heater driver shorted parameter

•	The IA Heater driver current parameter

•	The IA Heater driver open parameter

•	The IA Heater driver ground parameter

2. With the ignition ON, use a scan tool to observe the Intake Air Heater parameter for a normal range between 12.8-16 volts.
3. Observe that the IAH can be command ON with a scan tool.
4. Engine running, observe the DTC information with a scan tool. DTC P0540 should not set.
5. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Important: Perform the Circuit/System Verification before proceeding with Circuit/System Testing.

1. Probe the battery positive circuit at the IAH with a test lamp connected to ground, and observe that the test lamp illuminates.

⇒	If the test lamp does not illuminate, test the battery positive circuit for an open, a short to ground, or high resistance.

2. Observe that the IA Heater Driver Ground parameter displays OK with a scan tool.

⇒	If the IA Heater Driver Ground displays fault, inspect that the IAH is grounded properly to the air intake tubes, or for a faulty IAH.

3. Test the following circuits for an open, a short to ground, or a short to voltage:

•	The IAH temperature signal circuit

•	The IAH command 1 circuit

•	The IAH command 2 circuit

•	The IAH current signal circuit

•	The IAH voltage signal circuit

•	The IAH feedback signal circuit

•	Repair any circuit, as necessary.

4. Connect any circuits that were disconnected. With the ignition ON and the engine OFF, observe that the scan tool displays the IA Heater Driver Shorted Open parameter as OK.

⇒	If the IA Heater Driver Shorted Open parameter displays Fault, replace the intake air heater.

5. With the ignition ON and the engine OFF, observe that the scan tool displays the Glow Plug Driver Shorted Open parameter as OK.

⇒	If the Glow Plug Driver Shorted Open parameter displays Fault, replace the Glow Plug Control Module.

6. With the ignition ON and the engine OFF, observe the GPCM data display with a scan tool.

⇒	If the glow plug undervoltage displays Fault, and the IA heater undervoltage displays OK, replace the GPCM.

⇒	If the glow plug overvoltage displays Fault, and the IA heater overvoltage as OK, replace the GPCM.

⇒	If the glow plug undervoltage displays OK, and the IA heater undervoltage displays Fault, replace the IAH.

⇒	If the scan tool displays the glow plug overvoltage as OK, and the IAH overvoltage as Fault, replace the IAH.

7. Disconnect the IAH and measure between the temperature circuit on the IAH and a good ground for 15,000-18,000 ohms with a DMM.

⇒	If the DMM does not measure between 15,000-18,000 ohms, replace the IAH.

8. Turn ON the ignition and measure between the temperature circuit on the harness side and a good ground for 2-3 volts with a DMM.

⇒	If the DMM does not measure between 2-3  volts ohms, replace the GPCM.

Important: Set the DMM to the 4 v AC hertz scale.

9. With a DMM measure between command 2 circuit and a good ground on the harness side of the connector for 0.78-1.1 Hz.

⇒	If the DMM does not measure between 0.78-1.1 Hz ohms, replace the GPCM.

Important: 

•	Do not install the jumper wire between 12 volts and the command circuit for more the 20 seconds.

•	Set the DMM to the 4 v AC hertz scale.

10. Turn OFF the ignition. Install a jumper wires between the IAH and the IAH harness for the temperature signal circuit and command 2 circuit. Install a jumper wire between 12 volts and the command 1 terminal on the IAH. Turn ON the ignition. With a DMM measure for 1 hertz on the following circuits:

•	Current signal

•	Voltage signal

•	Feedback signal

⇒	If the DMM measures 0.7-1.1 hertz for all 3 circuits, replace the GPCM.

⇒	If the DMM does not measure 0.7-1.1 hertz for any of the 3 circuits, replace the IAH.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.