Engine management system - EDC (Maf): Description and operation

The IAT sensor incorporates a Negative Temperature Coefficient (NTC) thermistor in a voltage divider circuit. As the temperature of the intake air increases, the resistance in the thermistor decreases. As the thermistor allows more current to pass to earth, the voltage sensed at the ECM decreases. The change in voltage is proportional to the temperature change of the intake air. From the voltage output of the sensor, the ECM can correct the fuelling map for intake air temperature. This correction is an important requirement because hot air contains less oxygen than cold air for any given volume.

Inputs to the MAF sensor are a 12 volt supply from the engine compartment fuse box and an earth path connection. There are two outputs from the MAF sensor, these are in the form of a signal and signal return connection to the ECM. The IAT sensor utilises a 5 volt reference input from the ECM and shares the earth path of the MAF. The output from the IAT is calculated within the ECM by monitoring the changes in the reference voltage which supplies the IAT voltage divider circuit. The MAF/ IAT sensor connector has gold plated terminals.

Normal operating parameters of the MAF/ IAT sensor are as follows:

MAF

IAT