GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Isuzu 🢒 1999 🢒 S/T Isuzu - 4WD 🢒 DTC 🢒 DTC P0112 Intake Air Temperature (IAT) Sensor Circuit Low Voltage

Object Number: 376597 Size: SF
Engine Controls Components
Cell 20: MAP, IAT, TPS and ECT Sensors
OBD II Symbol Description Notice
Powertrain Control Module Connector End Views
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The Intake Air Temperature (IAT) sensor is a thermistor which controls the signal voltage to the PCM. The PCM supplies a 5V reference and a ground to the sensor. When the air is cold, the resistance will be high. Whenever the intake air is warm, the resistance will be low.

Conditions for Running the DTC
    • The engine run time is more than 320 seconds.
    • The vehicle speed sensor indicates that vehicle speed is more than 15 mph (24 km/h).

Conditions for Setting the DTC

The IAT sensor signal voltage indicates that the intake air temperature is more than 128°C (262°F) for 3.125 seconds.

Action Taken When the DTC Sets
    • The Malfunction Indicator Lamp (MIL) illuminates after two consecutive ignition cycles with the malfunction present.
    • The PCM records the operating conditions at the time the diagnostic fails. The Freeze Frame and Failure Records buffers stores this information.
    • A history DTC is stored.
    • The PCM will default to 60°C (140°F) for intake air temperature. The scan tool will not show the defaulted value.

Conditions for Clearing the MIL/DTC
    • The malfunction indicator lamp (MIL) will turn OFF after 3 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.
    • Use a scan tool to clear the DTCs.

Diagnostic Aids
    • When the vehicle is at ambient temperature, compare the IAT sensor to the ECT sensor. The IAT sensor and the ECT sensor should be relatively close to each other.
    • Use the Temperature vs Resistance Values Table below to evaluate the possibility of a skewed sensor. Refer to Temperature Versus Resistance .

Test Description

The number(s) below refer(s) to the step number(s) on the Diagnostic Table.

  1. The Powertrain OBD System Check prompts you to complete some of the basic checks and to store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data captured when the malfunction occurred. The scan tool stores this data for later reference.

    2.

  2. This step simulates a DTC P0113 condition. If the scan tool displays the specified value, the IAT signal circuit and the PCM are OK.

    3.

  3. Reprogram the replacement PCM and perform the crankshaft position system variation learn procedure. Refer to the latest Isuzu Technical Communications System (ITCS) information for PCM programming and the Crankshaft Position System Variation Learn for the crankshaft position system variation learn procedure.

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

Step

Action

Value(s)

Yes

No

1

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2
  1. Turn ON the ignition switch leaving the engine OFF.
  2. Install a scan tool.

Is the IAT sensor value greater than the specified value?

128°C (262°F)

Go to Step 4

Go to Step 3

3
  1. Review the Freeze Frame data and record the parameters.
  2. Start the engine.
  3. Operate the vehicle within the Freeze Frame conditions and Conditions For Setting The DTC as specified in the supporting text.

Is the IAT sensor value greater than the specified value?

128°C (262°F)

Go to Step 4

Go to Diagnostic Aids

4

  1. Turn OFF the ignition switch.
  2. Disconnect the IAT sensor electrical connector.
  3. Turn ON the ignition switch leaving the engine OFF.

Is the IAT sensor value below the specified value?

-30°C (-22°F)

Go to Step 5

Go to Step 6

5
  1. Turn OFF the ignition switch.
  2. Check for a poor electrical terminal connection at the IAT sensor.
  3. If the electrical connection is OK, replace the IAT sensor. Refer to the Intake Air Temperature Sensor Replacement .

Is the action complete?

--

Go to Step 10

--

6
  1. Turn OFF the ignition switch.
  2. Connect a test light to B+.
  3. Probe the IAT sensor signal circuit terminal at the IAT sensor electrical connector.

Does the test light illuminate?

--

Go to Step 7

Go to Step 9

7
  1. Turn OFF the ignition switch.
  2. Disconnect the PCM electrical connector.
  3. Connect a test light to B+.
  4. Probe the IAT sensor signal circuit terminal at the IAT electrical connector.

Does the test light illuminate?

--

Go to Step 8

Go to Step 9

8

Repair the short to ground in the IAT sensor signal circuit. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

--

Go to Step 10

--

9

  1. Check for a poor electrical terminal connection at the PCM.
  2. If the electrical connection is OK, replace the PCM. refer to the Powertrain Control Module Replacement .

Is the action complete?

--

Go to Step 10

--

10
  1. Using the scan tool, clear the DTCs.
  2. Start the engine.
  3. Idle the engine at the normal operating temperature.
  4. Operate the vehicle within the conditions for setting this DTC as specified in the supporting text.

Does the scan tool indicate that this diagnostic ran and passed?

--

Go to Step 11

Go to Step 2

11

Check to see if any additional DTCs are set.

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

--

Go to applicable DTC table

System OK