Mass Air Flow/Intake Air Temperature (MAF/IAT) Sensor The MAF/IAT sensor is located on the engine air intake manifold. The sensor combines the two functions of a MAF sensor and an IAT sensor in one unit. The sensor is housed in a plastic moulding which is connected between the intake manifold and the air intake pipe. The MAF sensor works on the hot film principle. Two sensing elements are contained within a film. One element is maintained at ambient (air intake) temperature, e.g. CF. The other element is heated to CF) above the ambient temperature, e.g. CF. Intake air entering the engine passes through the MAF sensor and has a cooling effect on the film. The ECM monitors the current required to maintain the CF) differential between the two elements and uses the differential to provide a precise, nonlinear, signal which equates to the volume of air being drawn into the engine. The MAF sensor output is an analogue signal proportional to the mass of the incoming air. The ECM uses this data, in conjunction with signals from other sensors and information from stored fuelling maps, to determine the precise fuel quantity to be injected into the cylinders. The signal is also used as a feedback signal for the EGR system. The IAT sensor incorporates a Negative Temperature Coefficient (NTC) thermistor in a voltage divider circuit. The NTC thermistor works on the principle of decreasing resistance in the sensor as the temperature of the intake air increases. As the thermistor allows more current to pass to ground, the voltage sensed by the ECM decreases. The change in voltage is proportional to the temperature change of the intake air. Using the voltage output from the IAT sensor, the ECM can correct the fuelling map for intake air temperature. The correction is an important requirement because hot air contains less oxygen than cold air for any given volume. The MAF sensor receives a V supply from the engine compartment fusebox and aground connection via the ECM. Two further connections to the ECM provide signal and signal ground from the MAF sensor.
ENGINE MANAGEMENT SYSTEM – TD 18-1-20 DESCRIPTION AND OPERATION The IAT sensor receives a V reference voltage from the ECM and shares aground with the MAF sensor. The signal output from the IAT sensor is calculated by the ECM by monitoring changes in the supplied reference voltage to the IAT sensor voltage divider circuit. The MAF/IAT sensor connector has gold plated pins to minimise resistance caused by poor connections. The following tables show the operating parameters for the MAF/IAT sensor.