Vehicles rely on an electronic device known as the mass air flow sensor in the electronic fuel injection system to measure the airflow through the intake. Signals are sent to the Engine Control Unit (ECU) or Powertrain Control Module (PCM) in order to control the fuel injection system for the proper air-fuel ratio and efficient combustion. It is important to know how to identify a bad mass air flow sensor before it causes major issues with your engine. Most common mass air flow sensor problems include rough running engine, increased exhaust fumes, backfiring, poor fuel economy and the ‘check engine’ light coming on.
Let’s examine the mass air flow sensor function and look at this component in greater detail.
How Does a Mass Air Flow Sensor Work in an Engine?
A common type of mass air flow sensor in use in most vehicles is the hot-wire type. It consists of an electrically heated wire to measure the amount of airflow entering the internal combustion engine, hence the name hot wire method. There is a temperature sensor placed close to the wire to measure the temperature of the flowing air. At idle, a minimal amount of air flows over the wire, requiring little electrical current to maintain the wire’s heat. When the throttle is opened, more air flows over the wire, cooling it down and requiring more electrical current to bring the wire back up to temperature. A sensor measures this electrical current and equates it to the amount of air flowing through the throttle body and into the engine. An electronic chip converts this electrical current into a digital signal that can be read by the ECU to control the fuel injectors and ignition timing. Various engine parameters can be adjusted based on these signals such as the air-fuel ratio, transmission shift points, etc.
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Mass Air Flow Sensor Problems
A problem with the mass air flow sensor can cause engine problems and affect performance and fuel efficiency. It is important to identify issues with the mass air flow sensor before they cause permanent damage or leave you stranded in the middle of the highway. Some common faults with a mass air flow sensor include:
Reduced Engine Performance:
A mass air flow sensor that is providing inaccurate readings to the ECU will cause disruption in fuel ignition, ignition timing and throttle response. The ECU will either add more fuel or less fuel into the cylinders which may result in poor acceleration, rough idling, inability to maintain speed, overheating, difficult starting and unexpected engine stalling.
Dashboard Warning Light:
The instrument cluster will display a ‘check engine’ light when there is a problem with the mass air flow sensor. The onboard computer can identify error signals from sensors around the engine with high accuracy and report these issues to the driver with an OBD scanner.
The engine can stall while driving without accurate air flow readings from the intake. The amount of fuel required at various driving conditions and stages will not be enough to sustain internal combustion effectively. You may have trouble starting the engine once it stops.
Engine rpms may rise and fall without throttle input as the sensors try to find their bearings. It may be impossible to drive smoothly with the engine hesitating to produce adequate power.
Decreased Fuel Efficiency:
With improper air flow calculations, the fuel injectors may dump excess fuel in the cylinders which go unburned. This will increase fuel consumption and you may find yourself filling up with petrol more often than usual. This can also lead to issues with your ignition system and catalytic converter.
Automatic transmissions change gears based on signals sent from various sensors around the engine. If any of these sensors are sending incorrect readings, it will cause jerky shifts or malfunctioning of the transmission system.
It is important to note that a malfunctioning mass air flow sensor may be the result of other faulty components. A dirty air filter will restrict airflow and debris may end up on the mass air flow sensor causing inaccurate readings. Vacuum leaks in the air intake can also cause issues. Finally, electronic and electrical issues may be a cause for concern regarding mass air flow sensors.
How Do I Maintain the Mass Air Flow Sensor?
Mass air flow sensors typically last for 100,000 km on average with standard driving conditions and regular maintenance. You can take the extra steps to keep your mass air flow sensor in good shape by avoiding stop-and-go traffic as much as possible and by using good quality unleaded fuel.
Mass air flow sensor cleaning is required when dirt and debris accumulate on it. The mass air flow sensor is located in the intake duct before the throttle body. Carefully disconnect the electrical connections from the sensor. Avoid the use of harsh chemicals or solvents, instead use a clean cloth and brush to clean it.
Ensure that your air filter is clean and free of dirt and debris. Extreme temperatures can cause problems with the mass air flow sensor, so avoid parking your car in direct sunlight or outside in cold weather.
Cleaning a mass air flow sensor is only a temporary fix because if the sensor is damaged or worn out, it needs to be replaced. Not all mass air flow sensors are the same and some require additional care and handling depending on their specifications. So it is best to refer to the vehicle’s service manual or to consult a qualified technician if you are having problems with the functioning of your mass air flow sensor.
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The Easiest Way to Fix a Mass Air Flow Sensor
Perhaps the simplest way to detect and fix a problematic mass air flow sensor is with an OBD scanner (On-Board Diagnostic) device. It can detect problems with the engine and emission systems.
The following steps can be used to fix a mass flow sensor:
- Connect the OBD scanner to the vehicle diagnostic port, usually located below the dashboard.
- Turn on the ignition without starting the engine
- Follow the OBD scanner prompts to find the diagnostic trouble codes
- Look for trouble codes such as P0100 which indicate a malfunctioning mass air flow sensor
- Refer to the troubleshooting procedures in the vehicle’s owner's manual
- Inspect the sensor for signs of damage, wear and tear
- Clear the trouble codes from the ECU and test drive the car
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Without an airflow sensor in your car, you probably wouldn’t be able to drive for long without running into serious issues. The ECU simply will not be able to control the fuel injectors and ignition timing without a proper air-fuel ratio, resulting in an engine that will either run roughly or, will completely seize.
With this article, you should have a better understanding of mass air flow sensor working principles, common problems and ways to get around them.
You can find more interesting articles on the Carorbis blog on topics such as How Do You Know If Your Throttle Position Sensor Is Working? and Types of fuel used in cars in India
Frequently Asked Questions
Q1. What is a Mass Air Flow Sensor?
Ans. A mass air flow sensor is a component found in a vehicle engine that measures the amount of air flowing into it. It is located in the air intake system before the throttle body to calculate the airflow and sends these signals to the Engine Control Unit (ECU) in order to control the fuel injection and ignition parameters.
Q2. How to Tell if You Have a Bad Mass Air Flow Sensor?
Ans. The first sign of a bad mass air flow sensor is a drop in engine performance. You may have trouble accelerating or maintaining speed on the highway. Rough idling may occur when the vehicle is stopped due to improper air-fuel ratio entering the cylinders. The engine may be running on a rich mixture (too much fuel) or lean mixture (too little fuel) which may cause a drop in fuel efficiency, increased emissions and engine overheating. A good way to check for a bad mass air flow sensor is to connect an OBD (Onboard Diagnostic Device) to your car and look for error codes that indicate a problem with the mass air flow sensor.
Q3. How Do You Perform Mass Air Flow Sensor Testing?
Ans. Some common methods for mass air flow sensor testing include:
Using a digital multimeter: The resistance of the mass air flow sensor is compared with the manufacturer’s specifications. If the reading is not within the specified range, it could indicate a malfunctioning mass air flow sensor.
Using an OBD scan tool: These scanners can identify faults in the mass air flow sensor by reading live data from the specified components. A diagnostic error code is displayed if the mass air flow sensor is faulty.
Physical damage: inspecting the mass air flow sensor for signs of damage or wear and tear, broken wires. Testing for vacuum leaks in the air intake or other issues that could affect the mass air flow sensor signal.
Smoke check: Injecting smoke into the intake system and observing if smoke is visible through the mass air flow sensor signal.
Q4. How Much is a Mass Air Flow Sensor?
Ans. The cost of a mass air flow sensor will depend on several factors such as the make, model and year of the vehicle, the brand of the component and whether you are purchasing a new or refurbished part. The average cost is in the range of Rs.10,000 – Rs.15,000. Since this is a complicated replacement, it will require the services of a trained mechanic to get the job done right. Therefore, you must factor in the cost of labour and service. High-end luxury cars may have more expensive mass air flow sensors that incorporate advanced electronics and technology, so it is better to check with your dealership regarding the specific cost for your vehicle.
Q5. When to Replace Mass Air Flow Sensor?
Ans. Even if the mass air flow sensor is not showing any signs of malfunction, it is recommended to replace the component after 100,000 km as the sensor gets damaged over time and can degrade in performance due to normal wear and tear. Signs that you need to replace a mass air flow sensor include:
Difficulty starting, rough idling, poor engine performance, stalling and jerky driving.
Increased exhaust emissions, poor fuel economy and a ‘check engine’ light on the instrument cluster.
Symptoms persist beyond cleaning the mass air flow sensor.
Physical damage or visible signs of wear and tear to the mass air flow sensor.
Q6. When to Clean Mass Air Flow Sensor?
Ans. It is generally recommended to clean Mass air flow sensors every 45,000 km or as part of the maintenance schedule. The frequency of mass air flow sensor cleaning will also depend upon:
Driving conditions – dusty conditions may require more frequent cleaning of the mass air flow sensor and air filters.
Air filter – the condition of the air filter will affect the mass air flow sensor. A dirty or clogged air filter will need to be cleaned or replaced.
‘Check engine’ light – If the diagnostic tool indicates a problem with the mass air flow sensor, then it is advisable to clean the sensor.
If you experience drivability issues such as poor performance, reduced acceleration or increased fuel consumption, it could mean that the fuel mixture is running rich or lean. Clean the mass air flow sensor if you notice these symptoms.
Q7. What is a Mass Air Flow Sensor Problem?
Ans. Some of the symptoms of a bad mass air flow sensor include:
Poor drivability such as engine stalling, hesitation, reduced performance and acceleration, especially when driving uphill or on the highway.
Rich air-fuel mixture which means there’s excess fuel and not enough air. This results in increased emissions, rough idling, and ‘check engine’ light.
Lean air-fuel mixture which means there’s not enough fuel and too much air. This may result in engine stalling, difficulty in starting, ‘check engine’ light.
OBD-II scanner will display an error code indicating issues with the mass air flow sensor. This could be caused by damage to the intake air filter or boot, vacuum leaks or a clogged exhaust system.