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Integrated into a vehicle’s engine management system.The full name is mass air flow sensor, usually referred to as MAF sensor, air flow meter, sometimes referred to as MAF. While it may go by many names, it does only one very important job: measuring the amount of air entering the engine. The ECU or PCM then uses this information to calculate the correct amount of fuel required for the optimum air-fuel ratio. Of course, without this information, the ECU will not be able to precisely control the fuel injection, resulting in the engine idling roughly or, worse, not idling at all. MAF sensor failures can be difficult to diagnose as many other parts (i.e. faulty spark plugs, wires, injectors, etc.) may reflect these symptoms. However, with some expert advice from OE manufacturer Delphi Technologies, you’ll know what’s causing the failure, what to look out for, and most importantly, how to replace it when it does.
How does a MAF sensor work?
Most MAF sensors are mounted on the intake duct between the air cleaner housing and the intake manifold and work on the hot wire principle. In short, the MAF has two sensing lines. One is heated by the current and the other is not heated by the current. As air flows over the heated wire, it is cooled. When the temperature difference between the two sensing wires changes, the MAF sensor automatically increases or decreases and compensates for the current flowing through the heating wires. The current is then converted to frequency or voltage and sent to the ECU to be interpreted as airflow. Adjust the amount of air entering the engine accordingly.
Why do MAF sensors failed?
Since the MAF sensor is responsible for measuring air flow into the engine, a lot of air passes through them. In fact, for every liter of fuel used, more than 9,000 liters of air can flow through the engine. There’s a lot of air here! And with that comes the potential for a lot of contamination. Dust, dirt and other debris can penetrate the sensor and are one of the main causes of MAF failure.
Such contamination can occur as early as 18,000-25,000 miles, depending on the vehicle model. For example, in small or compact cars, the MAF sensor can clog more quickly because it is located in a smaller engine compartment with a higher risk (oil vapor flows and combustion debris) in critical areas. In this case, the replacement becomes the equivalent of a long-drain oil service…it becomes almost a maintenance-type repair.
Other common failure problems include:
- A contact fault at the electrical connections
- Damaged measuring elements
- Mechanical damage from vibrations or an accident
- Measuring element drift (exceeding the measuring framework)
What to look out for in a failing MAF sensor?
When the MAF sensor goes bad, the engine doesn’t know how to add the right amount of fuel, causing several common symptoms:
- Check Engine Light: As with most engine management components, a problem with the MAF sensor often causes the check engine light to come on.
- The engine is running at full idle or under load: this usually points in the direction of the contaminated hot wire.
- Engine runs rich or lean: Caused by the MAF constantly misreporting air flow to the engine – diagnostics required to confirm this.
- Rough Idle or Stall: A broken MAF sensor does not transmit airflow information to the ECU, preventing it from accurately controlling fuel.
- Excessive vibration in place.
- RPMs change significantly without driver input.
Troubleshooting a MAF sensor
Consider the following steps to identify the source of MAF sensor malfunctions:Perform an electronic test of the MAF sensor and read the trouble codes with a diagnostic tool.
- Check the connection for proper fit and good contact.
- Inspect the MAF sensor and gauges for damage.
- Check the voltage supply with the ignition on (a circuit diagram is required to determine the needle). Reference value: 7.5-14V.
- Check the output voltage or frequency when the motor is running (a circuit diagram is required to determine the needle). Reference value: 0.5 V from 0 to 12,000 Hz respectively.
- Check the connection cables between the removed control unit connector and the sensor connector for transfer (necessary circuit diagram to determine pain). Reference value: about 0 ohms.
Common fault codes
Common fault codes and causes include:
- P0100: MAF circuit malfunction
- P0101: MAF circuit range/performance
- P0102: MAF circuit low input
- P0103: MAF circuit high input
- P0104: MAF circuit intermittent
- P0171 system too lean (bank 1) and P0174 system too lean (bank 2) are also often caused by a faulty or contaminated MAF sensor.
How to replace a faulty MAF sensor?
Once you have determined that the MAF sensor may be at fault, the best practice is to follow these simple steps:
- First, connect the diagnostic tool to your vehicle. Select the correct make, model, year and engine code of a working vehicle, record fault codes and check the real-time data parameters of the MAF sensor. Then exit the diagnostic software and turn off the ignition.
- You also need to check the power, ground and wiring. Connect the oscilloscope. Ideally, a detonating lead should be used to prevent the wiring insulation from breaking through and causing a future wiring problem. Open the throttle and observe the pattern to get a reading.
- If it is determined that the MAF sensor is faulty, you will need to replace it. Remove the fitting and then the mounting screws. Then remove the sensor from its housing.
- Check the flow tube to make sure there are no cracks in the plastic housing. If present, the entire device must be replaced – not just the probe. If the flow pipe is crack-free, you can replace only the sensor probe.
- Remember that it is important to handle only the sensor connection. Never touch the electronics as this can damage the sensor probe.
- Carefully slide the new sensor probe into the flow tube, then tighten the fasteners and replace the connection.
- Reconnect the diagnostic kit and clear all fault codes. Start the engine and check for new trouble codes. Exit the diagnostic software and turn off the ignition. Finally, check if the check engine light is off and then do a road test.
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