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 P166C: Intake Air (IA) Heater Resistance.

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). 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 or a condition in the IAH a DTC will set.

    • 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

Conditions for Running the DTC

The IAH is commanded ON.

Conditions for Setting the DTC

The resistance in the IAH is more than a calibrated amount for more than 3 seconds.

Action Taken When the DTC Sets

DTC P166C is a type B DTC.

Conditions for Clearing the DTC

DTC P166C is a type B DTC.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

    •  Engine Control Module Connector End Views
    •  Engine Controls Connector End Views

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

    •  Scan Tool Data List
    •  Scan Tool Output Controls

Circuit/System Testing

Replace the intake air heater.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.