Mass Airflow (MAF) Sensor
The MAF sensor provides a signal to the PCM proportional to the intake air mass. The MAF sensor uses a hot wire sensing element to measure the amount of air entering the engine. The hot wire is maintained at a constant temperature above ambient. Air passing over the hot wire cools the wire. The current required to maintain the temperature of the hot wire is proportional to the airflow. The PCM calculates the required fuel injector pulse width in order to provide the desired air to fuel ratio.
The MAF sensor is a digital sensor that provides an output signal of varying frequency. The signals time period is proportional to the flow rate crossing the sensor. The greater the airflow the shorter the time period. The time period varies from 1480 microseconds at a low flow or idle condition, to 106 microseconds at a high flow rate condition.
The MAF/IAT sensor is located in the intake air tube between the air filter housing and the throttle body.
Motor Electronics Cooling System (MECS) Pump The motor electronics cooling system is required to maintain an acceptable operating temperature for the TCM. The TCM commands the MECS pump and operation using the MECSP circuit. The pump (located near the radiator) receives the MECSP command. The MECS pump is commanded on for a calibrated time when the vehicle is first started to degas the MECS system. The coolant in the system flows in a loop from the MECS pump, to the TCM, and then into the MECS radiator bottom hose port, out of the top hose port of the MECS radiator, and back into the MECS pump. The cooling system has a degassing system that is connected in parallel between the MECS radiator and the MECS pump. The degassing system bleeds air or gases into the degas reservoir.