How does the mass air flow sensor work on a 1991 Toyota Camry?

Answer 1

Mass Airflow Sensor

Operation

The Mass Airflow (MAF) sensor directly measures the mass of air being drawn into the engine. The sensor output is used to calculate injector pulse width. The (MAF) sensor is what is referred to as a "hot-wire sensor". The sensor uses a thin platinum wire filament, wound on a ceramic bobbin and coated with glass, that is heated to 200*C (417*F) above the ambient air temperature and subjected to the intake airflow stream. A "cold-wire" is used inside the (MAF) sensor to determine the ambient air temperature.

Battery voltage from the EEC power relay, and a reference signal and a ground signal from the PCM are supplies to the (MAF) sensor. The sensor returns a signal proportionate to the current flow required to keep the "hot-wire" at the required temperature. The increased airflow across the "hot-wire" acts as a cooling fan, lowering the resistance and requiring more current to maintain the temperature of the wire. The increased current is measured by the voltage in the circuit, as current increases, voltage increases. As the airflow increases the signal return voltage of a normally operating (MAF) sensor will increase.

Testing

1. Using a multimeter, check for voltage by back probing the (MAF) sensor connector.

2. With the key ON, and the engine OFF, verify that there is at least 10.5 volts between the VPWR and GND terminals of the (MAF) sensor connector. If voltage is not within specification, check power and ground circuits and repair as necessary.

3. With the key ON, and the engine ON, verify that there is at least 4.5 volts between the SIG and GND terminals of the (MAF) sensor connector. If voltage is not within specification, check power and ground circuits and repair as necessary.

4. With the key ON, and the engine ON, check voltage between GND and SIG RTN terminals. Voltage should be approximately 0.34-1.96 volts. If voltage is not within specification, the sensor may be faulty.