P0127 BMW Intake Air Temperature Too High
– Intake Air Temperature (IAT) sensor harness is open or shorted
– Intake Air Temperature (IAT) sensor electrical circuit poor connection
The Intake Air Temperature (IAT) sensor is variable temperature sensitive resistor that measures the temperature of the air in the intake system. Sensor resistance will change based on air temperature. The higher the temperature is, the lower the resistance. The Engine Control Module (ECM) provides a reference voltage and monitors the voltage drop between a fixed value internal resistance and the sensor resistance. This is called a voltage divider circuit.
IAT sensor values are used by the ECM processor to assist with the calculation of idle speed, fuel mixture and spark advance.
Inaccurate voltages from the IAT sensor may affect pulse-width, idle quality, and tail pipe emissions. Intermittent signals may cause hesitation, stumble and surging. If an IAT sensor failure accompanies an Engine Coolant Temperature (ECT) sensor failure, cooling fan operation may also be affected.
Some manufacturers incorporate the Intake Air Temperature (IAT) sensor as part of the Mass Air Flow (MAF) sensor (Air Flow Meter).