MAF Sensor Problems

I have seen cars misfire, some stall, and others won’t start. With a good understanding of the car’s operating principles, I know the MAF sensor is one of the possible causes. In this guide, I have compiled a list of the most common MAF sensor problems and how you can diagnose the problem with a scan tool.  

Symptoms of a Bad MAF Sensor

Considering that the Mass Air Flow sensor tells the computer the amount of air entering the engine, a faulty sensor means the computer can’t know the amount of air entering the combustion chamber, making it unable to balance the air and fuel for combustion. 

For example, when you accelerate rapidly, the throttle opens wider, allowing more air into the engine. The faulty MAF sensor fails to detect this increase in airflow and signal the ECU. 

As a result, the ECU fails to increase fuel injection to maintain the desired air-fuel ratio, resulting in poor combustion. Some of the symptoms that can signal a faulty Mass Air Flow sensor include:

Hesitant Acceleration 

Hesitant acceleration is when there is a form of delay when you press the gas pedal. As a result, the vehicle doesn’t pick up speed as expected when the accelerator is depressed. The car might feel like it’s trying to accelerate and then stumbles and jerks before picking up speed.

Usually, this indicates the Mass Air Flow sensor is unable to detect the correct amount of air entering the engine, leading to inefficient combustion. However, you might experience the same signs when:

• The air filter is clogged. 
• There are problems with the fuel system, such as dirty fuel injectors, a clogged fuel filter, or a malfunctioning fuel pump. 
• There are issues with spark plugs issues, such as fouled spark plugs. 
• When the throttle body sensor is failing 

Black Smoke From the Tailpipe

Black smoke coming from the tailpipe is a sign of incomplete combustion and indicates that the engine is burning more fuel than it should. The most common cause of this problem is when the car is running rich, meaning there’s too much fuel and not enough air in the combustion chamber. 

For instance, most gasoline engines use an air-fuel ratio of 14.7:1. If the MAF sensor over-reports the amount of air entering the engine and tells the ECU that more air is coming in than there actually is, the ECU will think it needs to inject more fuel than required. 

With this rich mixture, not all the fuel gets burned during combustion because there isn’t enough oxygen to support complete combustion. This unburned fuel then exits the engine in the form of black sooty smoke. Usually, this is accompanied by poor gas mileage.

Hard Start

Is your engine taking longer than usual to start after turning the ignition key or pressing the start button? The MAF sensor might be the problem. 

If the MAF sensor sends incorrect data to the ECU—either over-reporting or under-reporting the amount of air entering the engine—the ECU can miscalculate the necessary fuel amount. This can result in either a too-rich or too-lean mixture. 

A rich condition can flood the engine with fuel, while a lean condition might not provide enough fuel for ignition. Also, if the MAF sensor inaccurately reads the air temperature, the ECU might not adjust the air-fuel mixture correctly for the cold conditions, leading to hard starts.

Check Engine Light

When the ECU detects readings from the sensor are out of expected parameters, or if the sensor’s signals are erratic or absent, it can set a Diagnostic Trouble Code (DTC) and illuminate the check engine light to alert you of the potential issue.

Keep in mind that the check engine light can illuminate because of a wide variety of issues affecting the engine performance, and you need to scan with an OBD-II scanner to confirm that it’s the Mass Air Flow sensor throwing the error code. 

How to Test MAF Sensor With Scan Tool

If the check engine light comes on and you suspect the MAF, you can use the OBD-II scanner to identify the stored trouble codes related to the sensor.

Usually, the scan tool will give you the following error codes depending on the car model and whether the sensor has malfunctioned, giving readings that are out of range, circuit low input, or circuit high input. 

• P0100: MAF Circuit Malfunction – This code suggests that there’s a problem with the sensor circuit.
• P0101: MAF Circuit Range/Performance Problem – This code indicates that the sensor signal is out of the expected range.
• P0102: MAF Circuit Low Input – This code is triggered when the sensor signal is lower than expected, which could be due to a short or a bad sensor.
• P0103: MAF Circuit High Input – Opposite of P0102, this code indicates that the sensor signal is higher than expected.
• P0104: MAF Circuit Intermittent – This code means the MAF sensor signal is intermittent or irregular.
• P1100: MAF Sensor Intermittent – Specific to some car models, indicating that the MAF sensor signal is sporadic.

Final Thoughts

Whether you are a new car owner or an experienced driver, understanding the above MAF sensor problems can help you know when it’s failing. You can also follow this guide to test the sensor with a multimeter and this cleaning guide to clean it if it’s dirty.