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.

The IAH feedback digital response signal to the GPCM is low and the IAH current is high.

DTC P154A is a Type B DTC.

DTC P154A is a Type B DTC.

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

1. Observe that the IAH Feedback CKT Status parameter displays OK.
2. Observe that the IAH Driver Shorted parameter displays OK.
3. Engine running, observe the DTC information with a scan tool. DTC P154A should not set.
4. 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: You must perform the Circuit/System Verification before proceeding with Circuit/System Testing.

1. Test the IAH feedback signal circuit between terminal 27X2 of the GPCM and terminal 6X1 of the IAH for an open, a short to ground, or a short to voltage.

⇒	If a condition is found, repair as necessary.

2. Ignition OFF, disconnect the X1 harness connector of the IAH. Connect any other circuits that were previously disconnected.

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

3. Turn ON the ignition. With a DMM, measure between command 2 circuit terminal 3 of the connector and a good ground for 0.78-1.1 Hz.

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

Important: 

•	Do not supply 12 volts terminal 2 on the IAH for more than 20 seconds.

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

4. Turn OFF the ignition. Install a jumper wire between temperature signal circuit terminal 1 of the harness connector and the corresponding terminal on the IAH.
5. Install a jumper wire between the command 2 circuit terminal 3 of the connector and the corresponding terminal on the IAH.
6. Supply 12 volts to terminal 2 on the IAH.
7. Turn ON the ignition. Measure for 1 hertz on terminal 6 at the IAH.

⇒	If 0.7-1.1 hertz is measured on terminal 6, replace the GPCM.

⇒	If 0.7-1.1 hertz is not measured on terminal 6, replace the IAH.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.