P0112

CIRCUIT DESCRIPTION
The Intake Air Temperature (IAT) sensor is a thermistor which measures the temperature of the air entering the engine. The Powertrain Control Module (PCM) applies 5 volts through a pull-up resistor to the IAT sensor. When the intake air is cold, the sensor resistance is high and the PCM will monitor a high signal voltage on the IAT signal circuit. If the intake air is warm, the sensor resistance is lower causing the PCM to monitor a lower voltage. DTC P0112 will set when the PCM detects an excessively low signal voltage on the intake air temperature sensor signal circuit.

CONDITIONS FOR RUNNING THE DTC
^ DTCs P0502 or P0503 are not set.
^ The engine has been running for over 10 seconds.
^ Vehicle speed is more than 25 mph (50 kph).

CONDITIONS FOR SETTING THE DTC
^ IAT signal voltage indicates an intake air temperature more than 135°C (275°F).
^ The above conditions are present for at least 20 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.
^ Use a scan tool in order to clear the MIL and the DTC.

DIAGNOSTIC AIDS
Check for the following conditions:
^ A poor connection at the PCM-Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
^ A damaged harness-Inspect the wiring harness for damage. If the harness appears to be OK, observe the IAT display on the scan tool while moving connectors and wiring harnesses related to the IAT sensor. A change in the IAT display will indicate the location of the malfunction.
^ A skewed or mis-scaled IAT sensor-Refer to Temperature vs Resistance. [1][2]Computers and Control Systems

If DTC P0112 cannot be duplicated, the information included in the Failure Records data can be useful in determining vehicle mileage since the DTC was last set.

TEST DESCRIPTION

Steps 1-9:

The numbers below refer to the step numbers on the diagnostic table.
2. Verifies that the malfunction is present.
3. If DTC P0112 can be repeated only by duplicating the Failure Records conditions. The table may be used to test the IAT sensor at various temperatures to evaluate the possibility of a shifted sensor that may be shorted above or below a certain temperature. If this is the case, replace the IAT sensor.

If the IAT sensor appears to be OK, the malfunction is intermittent, refer to Diagnostic Aids.
7. This vehicle is equipped with a PCM which utilizes an electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.