P1111

DTC P1111 Intake Air Temperature (IAT) Sensor Circuit - Intermittent High Input:

Intake Air Temperature (IAT) Sensor Circuit:

CIRCUIT DESCRIPTION
The Intake Air Temperature (IAT) sensor is a thermistor located in the fresh air duct to the throttle body and is used to monitor the temperature of the air entering the throttle body. The Vehicle Control Module-A (VCM-A) applies 5 volts to the sensor on CKT 472. When the air is cool, the resistance in the sensor will be high and the VCM-A will sense a high voltage signal. If the air is warm, the sensor resistance will be low and the VCM-A will sense a low voltage signal. DTC P1111 is a type "D" DTC.

DTC P1111 WILL SET WHEN
^ No Engine Coolant Temperature (ECT) DTCs.
^ No Vehicle Speed Sensor (VSS) DTCs.
^ Vehicle speed is less than 1 mph.
^ Engine coolant temperature is greater than 85°C (185°F).
^ Intake Air Temperature (IAT) voltage greater than 4.9V.

ACTION TAKEN (VCM-A WILL DEFAULT TO)
The VCM-A will store DTC P1111 to history if an intermittent problem is detected.

DTC P1111 WILL CLEAR WHEN
The VCM-A will turn the MIL "OFF" after three consecutive trips without a fault condition present. A history DTC will be cleared if no fault conditions have been detected for forty warm-up cycles [coolant temperature has risen 22°C (40°F) from start-up coolant temperature and engine coolant temperature exceeds 71°C (160°F) that same ignition cycle] or the Tech 1 clearing feature has been used.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

Important
^ Be sure to use the same diagnostic test equipment for all measurements.

1. If IAT sensor temperature is less than -37°C (-34.6°F), then the conditions for the DTC are still present and the problem is not intermittent.
2. This test will bypass the IAT sensor and will confirm that the IAT signal circuit and the sensor ground circuit to the VCM-A are sound. Grounding the signal circuit will provide a low voltage input to the VCM-A. The VCM-A should recognize this low voltage and indicate a high IAT temperature.
3. This test will determine if the IAT sensor signal circuit is OK. If the scan tool indicates a high IAT temperature, the sensor ground is open. If the scan tool does not indicate a high temperature, the IAT signal circuit is open.

DIAGNOSTIC AIDS
A scan tool indicates the temperature of the ambient air entering the throttle body. The air temperature should be very close to the temperature of the outside air and should rise gradually as the engine warms up and the underhood temperature increases. If DTC P1111 is set, the problem is intermittent. Check for poor connections at the VCM-A and IAT sensor by wiggling the connector gently and monitoring IAT temperature or IAT voltage on the scan tool. If the voltage waivers, repair the connector that caused the waiver. Also, a sensor may become "skewed" or mis-scaled. The "Temperature vs. Resistance Value" scale at the bottom of the diagnostic chart will help to detect a "skewed" sensor.