P0112

DTC P0112 IAT Sensor Circuit Low Voltage




Circuit Description
The Intake Air Temperature (IAT) sensor is a thermistor which controls the signal voltage to the PCM. The PCM supplies a 5 V 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 greater than 320 seconds.
- The vehicle speed sensor indicates that vehicle speed is greater than 15 mph (24 kmph).

Conditions for Setting the DTC
The IAT sensor signal voltage indicates that the intake air temperature is greater 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 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 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
- A scan tool can 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 vs Resistance.

Steps 1 - 4:

Steps 5 - 9:

Steps 10 - 11:

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.
4. This step simulates a DTC P0113 condition. If the scan tool displays the specified value, the IAT signal circuit and the PCM are OK.
9. 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 CKP System Variation Learn Procedure for the crankshaft position system variation learn procedure.