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). The IAH is connected to the GPCM by the following circuits:

Power to the IAH is supplied by the battery positive voltage circuit. An open/high resistance or a short to ground on this circuit will also set DTC P154B.

Voltage at the IAH voltage signal circuit is 16 volts or more.

DTC P154B is a Type B DTC.

DTC P154B is a Type B DTC.

A loose connection on the battery positive voltage circuit at the terminal 1 X2 of the IAH, or at the 175A fuse terminal 1 X4 of the Underhood Fuse Holder, may cause this DTC to set.

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Description and Operation

Intake Air Heater System Description

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

1. With the ignition ON, observe that the IA Heater Undervoltage parameter displays OK. Observe that the IAH volts displays near ignition 1 signal volts.
2. Observe that the IAH can be commanded ON with a scan tool.
3. Engine running, observe the DTC information with a scan tool. DTC P154B 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. Connect a test lamp between the battery positive voltage circuit terminal 1 X2 at the IAH and ground. The test lamp should illuminate.

⇒	If the test lamp does not illuminate, test the circuit for an open/high resistance or a short to ground and repair as necessary.

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

•	The IAH command 1 circuit between terminal 31 X2 of the GPCM and terminal 2 X1 of the IAH

•	The IAH command 2 circuit between terminal 26 X2 of the GPCM and terminal 3 X1 of the IAH

•	The IAH voltage signal circuit between terminal 30 X2 of the GPCM and terminal 5 X1 of the IAH

⇒	If a condition was found on any of the circuits repair as necessary.

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

⇒	If the IA Heater Undervoltage parameter displays Fault, replace the intake air heater.

⇒	If the IA Heater Undervoltage parameter does not display Fault, replace the GPCM.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.