GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The intake air temperature (IAT) sensor is a variable resistor that measures the temperature of the air entering the engine. The IAT sensor has a signal circuit and a low reference circuit. The engine control module (ECM) supplies 5 volts to the IAT signal circuit and a ground for the IAT low reference circuit. If the ECM detects an excessively low IAT signal voltage, which is a high temperature indication, this DTC sets.

The following table illustrates the difference between temperature, resistance, and voltage:

IAT

IAT Resistance

IAT Signal Voltage

Cold

High

High

Warm

Low

Low

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0112 Intake Air Temperature (IAT) Sensor Circuit Low Voltage

Conditions for Running the DTC

    • DTC P0502 is not set.
    • The engine run time is more than 120 seconds.
    • The vehicle speed is more than 50 km/h (31 mph).
    • DTC P0112 runs continuously once the above conditions are met.

Conditions for Setting the DTC

The ECM detects that the IAT sensor is more than 149°C (300°F) for more than 10 seconds.

Action Taken When the DTC Sets

    • The malfunction indicator lamp (MIL) will illuminate after 3 consecutive trips with a fail.
    • The ECM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame/Failure Records buffers.
    • A history DTC is stored.
    • The ECM will substitute a default value for intake air temperature. The scan tool will not show the defaulted value.

Conditions for Clearing the MIL/DTC

    • The MIL will turn OFF after 4 consecutive ignition cycles in which the diagnostic runs without a fault.
    • A history DTC will clear after 40 consecutive warm-up cycles without a fault.
    • DTCs can be cleared by using the scan tool.
    • Disconnect the ECM battery feed for more than 10 seconds.

Diagnostic Aids

    • Test the IAT sensor at various temperature levels in order to evaluate the possibility of a skewed sensor. A skewed sensor can result in a driveability condition.
    • If the engine has sat overnight, the IAT sensor and the engine coolant temperature (ECT) sensor values should display within 3°C (5°F). Refer to Temperature Versus Resistance .
    • A high resistance on either the IAT sensor signal circuit or the IAT sensor low reference circuit may not set a DTC. Refer to Circuit Testing in Wiring Systems.
    • For an intermittent condition, refer to Intermittent Conditions .

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine Controls Connector End Views

1

Did you perform the Diagnostic System Check - Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

  1. Turn ON the ignition, with the engine OFF.
  2. Important: The DTCs must be cleared or a temperature of 20°C (68°F) will be displayed on the scan tool.

  3. Clear the DTCs with a scan tool.
  4. Observe the intake air temperature (IAT) sensor parameter with a scan tool.

Is the temperature more than the specified value?

130°C (266°F)

Go to Step 4

Go to Step 3

3

  1. Turn OFF the ignition for 30 seconds.
  2. Start the engine.
  3. 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.

Did the DTC fail this ignition?

--

Go to Step 4

Go to Diagnostic Aids

4

  1. Turn OFF the ignition.
  2. Disconnect the IAT sensor.
  3. Connect a DMM between the signal circuit of the IAT sensor and a good ground. Refer to Circuit Testing in Wiring Systems.
  4. Turn ON the ignition, with the engine OFF.

Is the voltage less than the specified value?

4.8 V

Go to Step 5

Go to Step 6

5

Test the signal circuit of the IAT sensor for a short to ground or a short to the IAT low reference circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 10

Go to Step 7

6

Test for an intermittent and for a poor connection at the IAT sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 10

Go to Step 8

7

Test for an intermittent and for a poor connection at the engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 10

Go to Step 9

8

Replace the IAT sensor. Refer to Intake Air Temperature Sensor Replacement .

Did you complete the replacement?

--

Go to Step 10

--

9

Replace the ECM. Refer to Engine Control Module Replacement .

Did you complete the replacement?

--

Go to Step 10

--

10

  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  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.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 11

11

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK