Scion 22204-21010 Meter Sub-Assy, Intake Air Flow

The Mass Airflow (MAF) sensor is mounted on the intake duct and consists of the hot wire of platinum, the thermo resistor, and the control circuit placed within the body of the plastic. It uses hot wire sensing element to measure molecular weight of air for intake into the engine. With the release of throttle more volume of air passes over the hot wire, and hence it cools down. The MAF sensor circuiting is worked in such a manner to maintain hot wire preset at specific temperature by regulating the flow of current through the element. Therefore, as the wire cools down, the PCM raises the current in endeavors to retain higher temperatures, and this leads to a fluctuating output voltage signal that the PCM records. The above signal is in the form of an analog waveform which is then converted to a digital waveform required in fuel injector pulse width modulation and controlling the injectors. If there is a failure in MAF sensor circuit an an indication as a check code will appear. When starting diagnosis, the ignition key should be in the OFF position, and then, remove the electrical connector from MAF sensor and pay attention to two mounting screws and connector. Subsequently pull out the MAF sensor after loosening two retaining bolts and then take out the O-ring from the air intake duct. Reassembly is basically the reverse of disassembly, but a new O-ring is fitted in-between the MAF sensor and the intake duct.

For reinstallation, follow the reverse of the removal process. Make sure to use a new O-ring to ensure proper sealing of the MAF sensor in the air filter housing.

A problem in the MAF sensor circuit will set a diagnostic trouble code.