Fast Car

How to Diagnose a Faulty Mass Air Flow Sensor

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. 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. 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. 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 flat-head 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. 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. 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, re-installed the sensors screws, reattach the air hoses and re-tightened the hose clamps. Check for missing tools as well. Close the hood 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.