P1112

DTC P1112 IAT Sensor CKT Intermittent Low Voltage




Circuit Description
The Intake Air Temperature (IAT) sensor is a thermistor located in the air inlet duct to the throttle Body. The IAT sensor has a signal circuit and a ground circuit. The signal circuit has 5 volts applied to it by the VCM. When the air is cool, the resistance of the IAT sensor is high and the VCM senses a high signal voltage. When the inlet air warms, the sensor resistance decreases and the VCM will detect a lower signal voltage at the signal circuit input.

This DTC is designed to detect intermittent low voltage signals on the IAT sensor signal circuit.

Conditions for Running the DTC
- No active VS sensor DTCs
- The vehicle speed is greater than 2 mph (3 km/h).
- The engine has been running for more than 100 seconds.

Conditions for Setting the DTC
The VCM detects an intermittent low IAT voltage while the engine is running and vehicle exceeds 2 mph (3 km/h)

Action Taken When the DTC Sets
The VCM stores the DTC in history if the VCM detects an intermittent problem.

Conditions for Clearing the MIL/DTC
- A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (coolant temperature has risen 22 °C (40 °F) from the startup coolant temperature and the engine coolant temperature exceeds 70 °C (160 °F) during the same ignition cycle.
- Use the scan tool Clear Information function.

Diagnostic Aids
The IAT sensor indicates the temperature of the ambient air entering the throttle Body. The IAT temperature should read very close to the temperature of the outside air and should rise gradually as the engine warms up and the underhood temperature increases. An intermittent short to ground in the IAT sensor signal circuit could result in a DTC P1112. Also, a sensor may become skewed or mis-scaled. The Temperature vs. Resistance Value Table will help to detect a skewed sensor. 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.

If a repair is necessary, then refer to Wiring Repairs or Connector Repairs.

Steps 1 - 5:

Steps 6 - 9:

Test Description
The numbers below refer to the step numbers on the diagnostic table.

IMPORTANT: Be sure to use the same diagnostic test equipment for all measurements.

2. If the IAT sensor voltage is less than 0.25 volts, then the conditions for the DTC are still present.
3. If any other non-intermittent DTCs are set go there first.