Circuit Description
The intake air temperature (IAT) sensor is a thermistor. The control module supplies the IAT sensor a reference voltage on the IAT sensor signal circuit and a ground circuit. When the IAT sensor resistance is high, indicating a cold sensor, the IAT sensor signal voltage remains near the supplied voltage and decreases the signal voltage as the sensor warms. The control module monitors the IAT sensor signal circuit in order to calculate the temperature of the air entering the engine.
This diagnostic trouble code (DTC) is designed to detect an IAT sensor signal voltage lower than possible in a normally operating IAT sensor.
Conditions for Running the DTC
| • | DTCs P0502 and P0503 are not set. |
| • | The vehicle speed is above 3 km/h (2 mph). |
| • | The engine has been running for more than 100 seconds. |
Conditions for Setting the DTC
The intake air temperature (IAT) sensor voltage is below a calibrated value for more than 5 seconds.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
Diagnostic Aids
The IAT sensor indicates the temperature of the ambient air entering the throttle body. The IAT sensor temperature should read very close to the temperature of the outside air. The IAT sensor temperature should rise gradually as the engine warms up and the underhood temperature increases. If DTC P1112 is set, the problem is intermittent. Test for a short to ground in the IAT sensor signal circuit. This may be accomplished by moving the PCM harness at various locations and monitoring the IAT temperature or the IAT voltage on the scan tool. If the voltage varies, look for a short to ground in the area of the harness that caused the variance. Also, a sensor may become skewed or mis-scaled. Refer to Temperature Versus Resistance .
An inteermittent may be caused by any of the following conditions:
| • | A poor connections |
| • | Rubbed through wire insulation |
| • | A broken wire inside the insulation |
Thoroughly inspect any circuitry that is suspected of causing the intermittent complaint. Refer to Intermittent and Poor Connections in Wiring Systems.
If a repair is necessary, refer to Wiring Repairs in Wiring Systems.
Test Description
The numbers below refer to the numbers on the diagnostic table.
Important: Use the same diagnostic test equipment for all the measurements.
-
If the IAT sensor temperature is more than 139°C (282°F), the conditions for the DTC are still present and the problem is not intermittent.
-
Disconnecting the IAT sensor harness connector will provide a high voltage input to the PCM. The PCM should recognize this high voltage and indicate a low IAT temperature on the scan tool. Disconnecting the IAT sensor harness could also set additional IAT related codes.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference:
| ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | ||
Is the IAT sensor temperature more than the specified value? | 139°C (282°F) | |||
Is the IAT sensor temperature near the specified value? | -39°C (-38°F) | |||
4 |
Did you find a problem? | -- | ||
5 | The DTC is intermittent. Are any additional DTCs stored? | -- | Go to the applicable DTC table | Go to Diagnostic Aids |
6 | Repair the short to the ground in the IAT sensor signal circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
7 | Replace the IAT sensor. Refer to Intake Air Temperature Sensor Replacement . Is the action complete? | -- | -- | |
8 | Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | -- | -- | |
9 |
Does the scan tool indicate the diagnostic Passed? | -- | ||
10 | Does the scan tool display any additional undiagnosed DTCs? | -- | Go to the applicable DTC table | System OK |
