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 less than 15 mph (24 km/h). |
| • | The IAT sensor signal voltage indicates that the intake air temperature is less than -40°C |
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 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 vs Resistance . |
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
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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.
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This step simulates a DTC P0112. If the PCM senses the change, the PCM and wiring are OK.
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This step will determine if the reason the PCM did not sense the change was due to a open ground or signal circuit or malfunctioning PCM.
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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 Powertrain Control Module (PCM) .
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to | ||
2 |
Is the IAT sensor value less than the specified value? | -30°C (-22°F) | ||
3 |
Is the IAT sensor value less than the specified value? | -30°C (-22°F) | Go to Diagnostic Aids | |
Is the IAT sensor value greater than the specified value? | 130°C (266°F) | |||
Jumper the IAT sensor signal circuit to ground. Is the IAT sensor value greater than the specified value? | 130°C (266°F) | |||
6 | Check for a poor connections at the IAT sensor electrical connector and replace any malfunctioning terminals if necessary. Was a repair necessary? | -- | ||
7 | Check the IAT sensor ground circuit for an open and repair as necessary. Was a repair necessary? | -- | ||
8 | Check the IAT sensor signal circuit for an open and repair as necessary. Was a repair necessary? | -- | ||
9 | Check for a poor IAT sensor ground or a poor IAT sensor signal circuit terminal connection at the PCM and repair if necessary. Was a repair necessary? | -- | ||
10 | Replace the IAT sensor. Refer to Intake Air Temperature Sensor Replacement . Is the action complete? | -- | -- | |
Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | -- | ||
12 |
Does the scan tool indicate that this diagnostic has ran and passed? | -- | ||
13 | Check if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | -- | Go to applicable DTC table | System OK |
