Mass Airflow (MAF)/Intake Air Temperature (IAT) Sensors
- Discovery & Range Rover
MAF/IAT sensor is located in the intake air duct between air filter and intake manifold. Ensure airflow directional arrow embossed in the top of the MAF/IAT sensor tube is pointed in the proper direction. MAF/IAT sensor is connected to ECM through a 5-pin connector and the engine harness.MAF sensor uses a hot-film element contained in intake air tube to monitor the amount of air being drawn into engine. MAF sensor contains two sensing elements, one element is controlled at ambient air temperature, while the other is heated 360°F (200°C) more than ambient temperature using battery voltage. As intake air passes over it, the heated element cools, which reduces the element resistance. In order to maintain the same relative temperature, more current is supplied to the heated element. This voltage increase change is supplied to ECM as a zero to 5 volt signal. Using the MAF signal, the ECM calculates the amount of intake air entering engine. This in turn is used by the ECM to determine injected fuel quantity necessary for optimum engine performance and low emissions.
MAF sensor receives battery voltage from engine compartment fusebox, and a 5 volt reference signal from the ECM. MAF sensor and IAT sensor share a common ground connection and each provide a separate signal input to the ECM.
As a default strategy for MAF sensor failure ECM will calculate a MAF value based on throttle position, engine speed and intake air temperature. A MAF sensor failure may result in hard engine starts, engine may not idle, poor throttle response and driveability, incorrect emissions, and/or a high long term fuel correction. During driving when depressing throttle, engine speed may drop before recovering. A fault is indicated by illumination of the MIL.
IAT sensor uses a thermistor with a negative temperature coefficient (as temperature increases, thermistor resistance decreases). Changes in resistance cause a change in input voltage at the ECM. ECM converts received voltage value to provide an indication of intake air temperature.
As a default strategy for IAT sensor failure ECM will substitute a default value for intake air temperature of 113°F (45°C). An IAT sensor failure may result in the catalyst monitoring being affected due to exhaust temperature model, warm-up ignition angle affected, ISC speed adaptation disabled, ISC actuator blocked test disabled, fueling adaptations disabled and/or condenser fan hot restart inhibited.