GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2001 🢒 Regal 🢒 Body and Accessories 🢒 Body Control System 🢒 DTC P1112

Circuit Description

The intake air temperature (IAT) sensor is a thermistor which measures the temperature of the air entering the engine. The powertrain control module (PCM) applies 5 volts through a pull-up resistor to the IAT sensor. When the intake air is cold, the sensor resistance is high and the PCM will monitor a high signal voltage on the IAT signal circuit. If the intake air is warm, the sensor resistance is lower causing the PCM to monitor a lower voltage. If the PCM detects an intermittently low signal voltage on the IAT sensor signal circuit, DTC P1112 will set.

Conditions for Running the DTC
    • DTCs P0501 or P0502 are not set.
    • The engine has been running for over 10 seconds.
    • The vehicle speed is greater than 40 km/h (25 mph).
    • The above conditions are present for at least 5 seconds.

Conditions for Setting the DTC

The IAT signal voltage intermittently indicates an intake air temperature greater than 135°C (275°F).

Action Taken When the DTC Sets
    • The control module stores the DTC information into memory when the diagnostic runs and fails.
    • The malfunction indicator lamp (MIL) will not illuminate.
    • The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records.
    • The driver information center, if equipped, may display a message.

Conditions for Clearing the DTC
    • A current DTC Last Test Failed clears when the diagnostic runs and passes.
    • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic.
    • Clear the DTC with a scan tool.

Diagnostic Aids

If the condition is intermittent, refer to Intermittent Conditions .

DTC P1112 - IAT Sensor Circuit Intermittent Low Voltage

Step

Action

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check-Engine Controls?

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Is DTC P0112 set?

Go to DTC P0112

Go to Step 3

3
  1. Test the signal circuit for an intermittent short to ground. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
  2. If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 4

Go to Diagnostic Aids

4
  1. Use the scan tool in order to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

Go to Step 5

Go to Step 2

5

With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

Go to Diagnostic Trouble Code (DTC) List

System OK