Introduction

Over my 50-year career in the auto repair industry, I replaced thousands of defective, contaminated, shorted or simply-worn out mass air flow sensors (MAF).

I first saw them when Oldsmobile Division began switching to electronic fuel injection in the early 1980s. In those days, new cars still on car carriers wouldn't start because of defective MAFs. Consequently, all dealership technicians got a crash course in what an MAF does, the symptoms of a bad or failing sensor, and how to understand their specific diagnostic trouble codes (DTC).

After leaving the industry to become a vocational educator, I spent one summer at a Ford electronics facility as part of an "Educator in the Workplace" internship. As an auto technician, it was fascinating to see how car parts are designed, manufactured and tested.

One department I visited tested empty MAF sensor housings before electronic components were installed. Sophisticated measuring devices ensured the housings were the correct size to 1,000th of an inch and there was no slag on any seams. All for an empty shell that cost less than a dollar!

Once all the electronics were installed, the MAF sensor went through another series of tests. That's because MAFs are one of the most critical sensors needed to make our vehicles run and perform efficiently and run smoothly.

According to auto repair expert Bernie Johnson, "Today, MAF sensors are one of the most reliable parts on our cars and trucks." However, they do get dirty, and that's where MAF sensor cleaners come in. Here's what you need to know.

About the Expert

Bernie Johnson has almost 50 years of experience in the auto repair industry as an Automotive Service Excellence (ASE), Oldsmobile and Hyundai master technician. He is also a state certified emissions and safety inspection inspector at Faulkner Hyundai in Philadelphia, Pennsylvania.

Keep Yourself Safe

Make sure the engine and sensor are cool, and the engine is off. Wear personal protection equipment. Read and follow all label safety instructions and directions when using spray MAF sensor cleaners, which are highly flammable. Work outdoors in a well-ventilated area.

FAQs

What is the mass air flow sensor?

A device that monitors the temperature and weight of air entering your engine. Your onboard computer (engine control module, aka ECM) needs that information to calculate the right amount of fuel for the engine to run properly under all operating conditions.

What does the mass air flow sensor do?

It heats a small, hot, delicate platinum wire or plate, then measures the current required to keep it at a constant temperature while air blows past it. The MAF sensor sends that information to the ECM, which then determines how much fuel to inject into the combustion chamber.

What happens when the mass air flow sensor is dirty?

Over time, dust, debris and oil particles stick and bake onto the hot wire/plate. Eventually, those particles insulate the wire/plate from the air stream. This causes drivability problems, makes the Check Engine Light (CEL) illuminate, and increases tailpipe emissions.

What are the signs of a failing mass air flow sensor?

Hard starting, stalling, rough idling, poor acceleration, black smoke from the exhaust, as well as poor gas mileage. A rotted-out or rusted MAF sensor hot wire/plate can keep your car from starting and needs to be replaced.

How much does it cost to replace the mass air flow sensor?

It depends. In my area (outside of Philadelphia, Pennsylvania) it runs from $300 to $375 — about $100 for labor and $275 for parts. (According to AAA, national labor rates range between $47 and $215 an hour.) This doesn't include diagnostic or other fees.

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