GM Service Manual Online
For 1990-2009 cars only

Diagnostic Instructions

    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provide an overview of each diagnostic category.

DTC Descriptor

DTC P154B: Intake Air (IA) Heater Voltage Signal Circuit

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

IAH Temperature Signal

--

P154D

P154D

IAH Command 2

P154B

P154B

P154B

IAH Voltage Signal

P154B

P154B

P154B

IAH Command  1

P154B

P154B

P0640

IAH Current Signal

P154C

P154C

P154C

IAH Feedback Signal

P154A

P154A

P154A

IAH Battery Positive Voltage

--

P154B

--

Circuit/System Description

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:

    • The IAH temperature signal circuit
    • The IAH command 1 circuit
    • The IAH command 2 circuit
    • The IAH voltage signal circuit
    • The IAH current signal circuit
    • The IAH feedback signal circuit
If there is a fault on any of these circuits, a DTC will set.

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.

Conditions for Running the DTC

    • The IAH is commanded ON.
    • The GPCM battery voltage is between 9.5-15 volts.
    •  DTC P154B runs continuously when the above condition is met.

Conditions for Setting the DTC

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

Action Taken When the DTC Sets

DTC P154B is a Type B DTC.

Conditions for Clearing the DTC

DTC P154B is a Type B DTC.

Diagnostic Aids

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

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Intake Air Heater System Description

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

  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.

Circuit/System Testing

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.
  2. If the test lamp does not illuminate, test the circuit for an open/high resistance or a short to ground and repair as necessary.
  3. Test the following circuits for an open, a short to ground, or a short to voltage:
  4. • 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.
  5. 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.
  6. 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.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Intake Air Heater Replacement
    •  Control Module References for GPCM replacement, setup, and programming