Vehicle Control Module (VCM-A) Only

DESCRIPTION
The Intake Air Temperature (IAT) sensor is a thermistor (a resistor which changes value based on the temperature of air entering the engine and is mounted in the intake air duct). Low temperature produces a high resistance (approximately 100,000 ohms at -40°C (-40°F) while high temperature causes low resistance (approximately 70 ohms at 130°C (266°F). The Vehicle Control Module (VCM-A) supplies a 5 volt signal to the sensor through a resistor in the VCM-A and measures the voltage across IAT. The voltage will he high when the intake air is cold and low when the air is hot. By measuring the voltage the VCM-A calculates the intake air temperature.

OPERATION
The IAT sensor signal is used to adjust spark timing according to incoming air density. The Tech 1 scan tool displays temperature of the air entering the engine, which should read close to ambient air temperature when engine is cold, and rise as underhood temperature increases. If the engine has not been run for several hours (overnight) the IAT sensor temperature and engine coolant temperature should read close to each other. A failure in the IAT sensor circuit should set DTCs P0112, P0113, P1111 or P1112. Refer to Diagnostic Trouble Code Charts. Under Computer and Controls/System Diagnosis/Procedures. Testing and Inspection