C ircuit Description
The intake air temperature (IAT) sensor is a thermistor that controls signal voltage to the PCM. When the air is cold, the sensor resistance is high, therefore the PCM will see a high signal voltage. As air warms, sensor resistance becomes less and voltage drops.
Conditions fo r Running the DTC
• The PCM performs this DTC diagnostic continuously.
• The engine coolant temperature is less than 42.5°C (109°F).
Conditions fo r Setting the DTC
• The Intake air temperature is more than or equal to 151°C (303°F).
• All of the diagnostic set conditions were met for 2 seconds.
Action Taken When the DTC Sets
• The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive drive trip that the diagnostic runs and fails.
• The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the Failure Records will store this information. If the diagnostic reports a failure on the second consecutive drive trip, the Freeze Frame records the operating conditions at the time of failure and updates the Failure Records.
Conditions fo r Clearing the MIL/DTC
• The PCM will turn the MIL off after three consecutive trips without a fault condition.
• A History DTC clears after forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures
• The use of a scan tool.
Diagnostic Aids
Check harness routing for a potential short to ground in the signal circuit. Refer to Symptoms. The scan tool displays intake air temperature in degrees centigrade. A skewed sensor could result in poor driveability complaints. Refer to Temperature vs Resistance.
An intermittent may be caused by any of the following conditions:
• A poor connection
• Rubbed through wire insulation
• A broken wire inside the insulation
Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Refer to intermittents and Poor Connections Diagnosis in Wiring Systems. If a repair is necessary, then refer to Wiring Repairs or Connector Repairs in Wiring Systems.
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
2. This step determines if P0112 is a hard failure or an intermittent condition.
3. This test will determine if the PCM can recognized an open sensor.
4. This step will determine if the problem is a short to ground or a malfunctioning PCM.
