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 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 Setting 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 km/h).
- The IAT sensor signal voltage indicates that the intake air temperature is greater than 125°C (262°F) for 3.125 seconds.

Action Taken When the DTC Sets
- The Malfunction Indicator Lamp (MIL) illuminates.
- 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.

Test Description





Number(s) below refer to the step number(s) on the Diagnostic Table.
1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored in the scan tool for later reference.
4. This step simulates a DTC P0113 condition. If the scan tool displays the specified value, the AT signal circuit, the PCM are OK.
8. Replacement PCMs must be reprogrammed and the crankshaft position system variation procedure must be performed. Refer to the latest Isuzu Technical Communication System (ITCS) information for programming procedures and also refer to the CKP System Variation Learn Procedure.