The mass air flow (MAF) sensor is a relatively simple component that plays a critical role in maintaining efficient combustion. In order to achieve the optimum ratio of air to fuel entering the cylinders, the ECM needs to keep track of both quantities.
Fuel can be precisely timed and measured through an injector, but air is a bit more of an unknown quantity. Altitude, temperature, and humidity can all affect the volume, density, and mass of incoming air, so the MAF sensor gives the ECM a “heads up” on the quantity and quality of that available air charge. The ECM can then use this information, as well as information from several other intake system sensors (manifold absolute pressure, throttle position, and intake air temperature) to estimate the amount of fuel required to help achieve the “perfect” ratio of 14.7 parts air to 1 part fuel required for efficient combustion at different engine loads. After the combustion process is complete, information from the oxygen sensor(s) is used to report back the success (or failure) of these adjustments, further refining the process.
Many modern MAF sensors are of the “hot wire” design, which rely on changes in the temperature and electrical resistance of a fine platinum filament as intake air passes over it. Over time, contaminants may build up on the sensor wire, insulating it and affecting the voltage signal being sent to the ECM. This false reading can lead the ECM to incorrectly adjust the amount of fuel trim needed for smooth operation. The results can be rough idle, stalling, stumbling and hesitation, as well as poor fuel economy.
Sensor wire contamination can often be traced back to a lack of regular air filter maintenance, or oil contamination from a poorly functioning PCV system. Oil contamination may also be caused by “over-oiling” reusable air filters, so care should be taken to follow the filter manufacturer’s recommendations when cleaning and oiling this type of element. A popular alternative to replacing a contaminated MAF is to attempt cleaning the sensor with a specialized aerosol spray.
Recommending these tune-up items and using these cleaners as part of a preventative maintenance schedule can actually help prolong the life of an original or replacement MAF sensor, so don’t be shy about asking for these add-on sales. When replacement of the MAF is necessary, the sensor may either be serviced as an assembly, or as an individual component. For remanufactured assemblies, be sure to inspect the customer’s sensor and housing carefully for any damage before accepting it as a core. For MAF sensors that require disassembly from their housing, your customers may also need to remove tamper-proof screws. Having these specialized bits on hand will make it more convenient for your DIY customers, who may be expecting to replace complete assemblies rather than individual sensors.
Finally, whenever your customer is servicing or replacing the MAF sensor, recommend inspection of the air intake hoses connecting the air box, MAF, and throttle body.