A good sign that your mass airflow sensor unit is getting dirty is that your car will start to hesitate when you press down on the gas pedal. There can be other reasons why your car is running rough, so you should take your car to an auto parts shop to have it checked. An auto parts store will usually test your car with a diagnostic scan tool to find the problem. A reading of P0171 on the scanner means the engine is running "lean" and it is also an indication that the mass airflow sensor needs to be cleaned. Here is how you can clean the mass air flow sensor on your 2003 Nissan Altima in an afternoon.

Location of Mass Air Flow Sensor

The mass air flow sensor slides into the duct work coming from the air filter to the fuel injection system. The air filter is located in the engine compartment near the bottom of the windshield. The duct work starts at the air filter and goes to the left toward the engine block. Where the ductwork begins is a part with electrical wires running to it. This is the mass airflow sensor.

Removing the Sensor

You should disconnect the cables running to your battery before you proceed to eliminate the chance you short out the sensor as you are removing it. Now, pull the electrical harness out from the top of the sensor to disconnect the wires running to it. There are a couple of small bolts holding the sensor bracket the duct work. Remove the bolts and take out the sensor.

Cleaning the Sensor

You should lightly tap the sensor to loosen and knock out any material that might be stuck in the opening on the sensor to measure air flow. Sometimes little particles that get sucked into the air flow system will get stuck in the opening in the sensor.

You want to get a can of mass airflow cleaner to thoroughly clean the sensor.  A mass airflow cleaner is specially formulated to remove the debris from the sensor heads, which capture the signals that are sent to the computer without causing them harm. Spray a liberal amount of cleaner on the sensor and allow it to air dry.

Installing the Sensor

After the sensor has dried, slip back into the slot on the air duct and bolt it back in place. Reattach the wire harness and the cables to the battery. You are now ready to start the car to make sure it is working better.

For professional help, contact a service like Leo's Automotive.