How to Know if a Mass Air Flow Sensor Is Bad

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One way to check to see if a mass air flow sensor has gone bad is by tapping on the engine when it's running to see if it stumbles. Find out how to remove a mass air flow sensor to check if it has gone bad with help from an ASE-certified master automobile technician in this free video on mass air flow sensors.

Part of the Video Series: Auto Repair & Maintenance
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Video Transcript

Today's modern automobiles have tighter emission controls and fuel economy standards than ever before. For vehicles that have one a mass air flow sensor is probably the one of the most important sensors as far as maintaining good fuel economy and good emissions. The computer will add the proper amount of fuel based on the amount of air coming in, so it's important that this sensor works correctly. In determining if you have a bad one there's a lot of different ways that they can go bad but one of the things that we'll look for when the engine is running is that if you tap on it, if the engine seems to stumble or anything like that, that would definitely be a sign of a bad mass air flow sensor. The next thing that we could do is if the engine's running very poorly and we suspect that the mass air flow sensor is the reason, simply unplug the mass air flow sensor. The computer will detect the error and go into a back up mode of operation. If the vehicle runs better when you do this, chances are the mass of mass air flow sensor is bad. Other than that, we're left two tests how we could use either the engine scanner to get information from the computer itself or a multimeter where a self scope in order to check the output of the mass air flow sensor itself. A typical test is to hook into the appropriate wire that is the output and what we'll do is we'll monitor the voltage as we raise the engine speed. So, we'll actually start the vehicle and we'll do that. Now, that the engine is running we have a voltage reading coming from the now attached receptor that's proportional to the amount of air flowing through the sensor and that should increase as we increase engine speed by opening the vial. If it is not increased its output proportion into the opening of vial then the sensor is bad.

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