How to diagnose a faulty mass air flow sensor

Written by tom lutzenberger
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How to diagnose a faulty mass air flow sensor
The MAF sensor works inside the hose leading from the air filter to the engine intake valve. (Jupiterimages/Photos.com/Getty Images)

The mass air flow (MAF) sensor in a vehicle plays a role in engine combustion and emissions control. As one of a number sensors built into an engine design, the sensor provides regular readings to the car's on-board diagnostic computer, telling it whether sufficient air is entering the engine or not. Because the sensor involves a very thin, sensitive wire as the reading mechanism, if it gets gunked up the readings can become faulty. Cleaning and retesting the sensor will determine if it needs replacing or just maintenance.

Skill level:
Easy

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Things you need

  • OBDII code reader
  • Shop vacuum
  • Screwdriver
  • Screwdriver with security Torx bits
  • Shop rag
  • MAF sensor cleaner
  • New air filter

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Instructions

  1. 1

    Connect a OBDII-type engine code reader to your car using the connection port underneath the steering wheel area. Turn the ignition to the "on" position but do not start the engine. Let the code reader connect with the car computer to see if it will generate a code for a faulty mass air flow sensor. Confirm whether the sensor is actually triggering a malfunction code or not. Erase the code stored in the computer using the reader tools. Turn the car off and disconnect the code reader.

  2. 2

    Raise the hood and locate the air filter box. Open the air filter box and pull out the old air filter. Use a shop vacuum to suck up all the debris, dust and dirt inside the filter box. However, do not poke the vacuum into the cavity going to the mass air flow sensor.

  3. 3

    Turn off the vacuum and use a screwdriver to disconnect the hose clamp holding the intake hose to the bottom of the mass air flow sensor going toward the engine. Pull the hose off and place it clear of the sensor. Carefully disconnect the wiring to the mass air flow sensor itself. Use the screwdriver to carefully push the connection tab free if the wiring junction uses a snap-lock to connect. Place it safely clear of the sensor unit.

  4. 4

    Use a screwdriver with a star-shape, or security Torx bit if the sensor is secured to the air filter box with screws having star-shape heads. Use a regular screwdriver if the screws are Phillips-head or flathead style. Carefully loosen and remove the sensor screws and put them in a safe place to avoid losing them. Use the shop rag to carefully twist the sensor back and forth by hand until it comes free from the air filter box.

  5. 5

    Move the sensor unit to a clear workspace. Put a shop rag underneath it and do not touch the sensor mechanism inside. Attach the spray nozzle to your bottle of mass air flow sensor cleaner and spray the sensor clean with five or six good sprays. Spray downward so the excess hits the rag underneath. Examine the wire inside without touching it to confirm it is clean. Let the unit air dry on the rag for 30 minutes.

  6. 6

    Reattach the sensor, without touching the inside wire mechanism, to the air filter box and following the above removal steps in reverse order. Install a new air filter in the air filter box and close it up. Confirm you reconnected the sensor wiring, reinstalled the sensor's screws, reattach the air hoses and re-tightened the hose clamps. Check for missing tools as well. Close the bonnet and restart the car. Let the engine warm up and drive it to check if the sensor gives off a trouble code again. Replace the sensor unit completely if it does.

Tips and warnings

  • Using a specific mass air flow sensor cleaner is the best solvent for cleaning a dirty sensor. You can buy the product at any auto parts store. Carburettor cleaner can work as well but it takes longer to dry. In any case, only a spray solvent cleaner should be used for cleaning the sensor.
  • Never, ever touch the wire mechanism inside the mass air flow sensor with anything, include tools or a spray cleaner hose. The wire is so sensitive, the slightest touch can damage it. Always let it air dry after cleaning. Do not dry it off with any kind of a rag or compressed air.

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