Genuine Volvo 740 Mass Air Flow Sensor

Volvo 740 Mass Air Flow Sensor Parts and Q&A

• Mass Air Flow Sensor
  8251497
  Q: What are the features and testing procedures for the Mass Air Flow Sensor on Volvo 740?

  A:

  The sensor inside the air mass meter has a wire that is kept at 250degF (120degC) above the ambient air temperature of incoming air. As the air mass increases, more current is required to maintain the correct wire temperature and this current is used to calculate the air mass intake. When the engine is shut off, any dirt on the wire gets burned off electrically by heating the element to 1832degF (1000degC) for 1 second; any tiny bit of dirt left could cause wrong signals to be sent to the control unit, resulting in a wrong air/fuel mixture. To test the MAF sensor, it is necessary to disconnect the connector, then by wiring diagrams find the signal ground wire and measure the resistance with a DVOM, it should be 0 ohms. Next, locate the signal circuit and measure the voltage between it and ground with ignition in ON position, it should be equal to battery voltage. After plugging the MAF sensor connector back in, backprobe the signal return and signal ground with the key in the ON position, expecting a voltage of 0.1 - 0.2v. If the voltage is okay, make sure all the connections are tight or change the MAF sensor. To remove it, disconnect the negative battery cable, unplug the sensor connector and remove the two retaining screws to remove the sensor. To install, fit the sensor into the air inlet hose, tighten the retaining screws on the sensor, plug in the connector and reconnect the negative battery cable.