The mass air flow (MAF) sensor on a 2003 Ford Expedition measures the amount of air entering the engine's combustion chamber and feeds that information to the power train control module. The module then adjusts the amount of fuel introduced to the combustion chamber in order to attain the optimal air-to-fuel ratio. If the MAF sensor incurs contamination, it can no longer provide proper air readings and you'll need to replace it. Anyone with basic auto-repair skills can change a mass air flow sensor on a 2003 Ford Expedition in less than 30 minutes.
Open the hood and manually disconnect the wiring harness from the MAF sensor. The sensor is located right behind the air filter housing, in the tube leading to the top of the engine.
Loosen the two clamps that hold the MAF sensor to the inlet and outlet tubes, using a socket set. Slide the clamps onto the tubes, away from the sensor, by hand.
Pull the old MAF sensor out of the engine bay, by hand, and set it in the box the new sensor came in. Place the new sensor in position, making sure that the flow arrow points towards the engine.
Slide the inlet and outlet tubes over the new MAF sensor, and then slide the clamps back into position. Tighten the clamps with the socket set.
Plug the wiring harness into the new MAF sensor.
