The most common symptoms of a bad mass air flow sensor are slow acceleration and reduced engine power. You may also notice a difference in fuel economy, as the mass air flow sensor's primary function is to let the engine know how much fuel to inject.
Signs that the MAF sensor may need cleaning include poor fuel economy, rough idling, or a check engine light related to air intake issues. In summary, while cleaning is important for maintaining performance, it should be done judiciously to avoid damaging the sensor.
Keep in mind: Sometimes, a bad MAF sensor won't set a code, especially on older vehicles with a type of self-diagnostics called OBD-1.
Although cleaning a contaminated MAF may seem to bring the performance back, it rarely brings it to 100 percent operation and accuracy. There are many instances where the internal circuitry is damaged or shorted. In these cases, the sensor needs to be replaced.
MAF sensors are designed to last the lifetime of your vehicle without breaking down. Build up of dirt and grime can reduce this lifespan, though, so it's important to keep an eye out for signs that the sensor is struggling.
Connect the black probe to a good ground point, such as the battery negative terminal or the engine block. Turn on the ignition key, but do not start the engine. The multimeter should read between 0.5 and 1.5 volts. If the voltage is out of range, the MAF sensor is bad and needs to be replaced.
After changing a mass air flow sensor, you should disconnect it from the car battery for around 15 minutes.
The Light Stays On
You may think that there is still a problem with the car after the repair, but it's because the light needs time to reset. The car's internal computer only resets after a set period where it checks all of its sensors once more. The reset can happen automatically after around 10 to 20 cycles.
The engine won't receive the proper airflow if you have a faulty mass airflow sensor. This, in turn, can lead to your car running roughly or the engine misfiring. That happens because the imbalance means that your powertrain control module can't determine how much fuel your engine needs to run.
Resetting the MAF Sensor by Idling
Gently unplug the wires leading into the sensor. Then, grab a screwdriver and remove the fasteners holding the sensor in place to remove it. On some newer, modern MAF sensors, you can press a small reset button instead of idling.
A mass air flow typically last between 80,000 miles to 150,000 miles. Proper maintenance of the mass air flow and cleaning it will help prolong its life. However, there are a few vehicle symptoms that will tell you when it is time to replace the air flow sensor. The first symptom is hard starting.
The process for replacement is pretty straightforward. If you haven't already located the MAF sensor, it should be between the air filter and intake.
In most cases, successfully repairing the issue that caused your light to come on will cause the check engine light to turn off automatically—but only after 10 to 20 “cycles”. A cycle, in this instance, refers to the process of turning the vehicle on, running it for some time, and turning it off again.
Disconnecting your battery and draining the power to cause an ECU reset is one of the most common fixes for a check engine light that won't go away on its own. Doing so is equivalent to a hard reboot on a desktop computer, which is a standard way to eliminate many common problems.
A faulty mass airflow sensor is a common reason why a check engine light comes on. If the engine control module receives a MAF error code, it will turn on the check engine light to let you know that there is a problem with the engine.
In the majority of contemporary car models, the Engine Control Unit (ECU) and Engine Control Module (ECM) undergo an automatic reprogramming process following the replacement of the Mass Air Flow (MAF) sensor.
Start by disconnecting the vehicle's battery to avoid any electrical mishaps during the replacement. Locate the MAF sensor. It's typically found between the air filter housing and the throttle body, and it's cylindrical. Refer to a service manual if you're unsure.
The car will revert to preprogrammed fueling maps that run rich, and it may pull timing too. Because of this, you'll likely see decreased mpg, rougher idle, and weaker acceleration. If you're doing this to try and diagnose a bad/dead mass air sensor, it won't take long at all.