Engine Troubleshoot

P0101 Mass Air Flow (MAF) Circuit Range/Performance

Mass Air Flow (MAF) Circuit/Performance Malfunction
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Written by The Motor Guy

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What Is Engine Code P0101?

  • P0101 Technical Definition: Mass Air Flow (MAF) Circuit Range/Performance
  • P0101 Meaning: A problem with the MAF sensor readings
  • Most common cause: Faulty/Dirty Mass Air Flow Sensor, possible air leak 
  • Risks for the engine/driver: LOW You should get it checked out ASAP but your car should be safe to drive
  • Emissions severity: HIGH. The car probably won’t pass emissions testing
  • Estimated repair time: 1-2 Days
  • Estimated repair cost: $100-300+ (if the MAF needs replacing it will be more expensive than just cleaning it)

The engine code P0101 is stored in memory when the ECU detects that the Mass Air Flow (MAF) sensor readings are outside the expected frequency range.

The Mass Air Flow Sensor is one of the main electronic components of the fuel delivery system. His job is reporting, in real time, the mass of air entering the engine. This information is used by the Electronic Controller Unit (ECU) to determine the amount of fuel needed to achieve the stoichiometric ratio consisting of 14.7 parts of air per each part of fuel.

This calculation is then adjusted after analyzing the data from the rest of sensors, especially the oxygen sensor feedback that is used as a key input for the corrections of the next computing cycle.

In other words,  without the MAF data, the ECU would be nearly blind regarding air flow making it very difficult to deliver the correct amount of fuel via the injectors. On modern vehicles, a “reference” MAF value is calculated by the ECU using the information from the rest of the engine sensors. This calculated value is compared to the actual MAF output in order to check the sensor performance. 

The P0101 code is stored when the ECU detects a significative variation between the calculated MAF value and the actual MAF value. 


7 Common Symptoms When Code P0101 is Present

If the MAF sensor is not working properly, it will not be able to send the ECU the correct air flow value. This means the ECU will not be able to calculate the correct amount of fuel each injector needs. Because of this, the most common symptoms associated with engine code P0101 are related to the performance of the engine.

Here are the most common symptoms:

  1. Check Engine Light on dashboard
  2. Difficulty starting the engine
  3. Poor fuel economy.
  4. Rough idle.
  5. Engine hesitation during acceleration.
  6. Engine hesitation under load.
  7. Gas smell from the exhaust pipe

Possible Causes For Error Code P0101

The most common causes of data trouble code P0101 are:

  1. MAF sensor wiring (open, shorted, burnt) 
  2. MAF sensor connector (loosely, corroded, disconnected or bent pins)
  3. Dirty or clogged MAF sensor
  4. Bad MAF sensor
  5. Intake manifold air leaks.
  6. Highly clogged or restricted air filter
  7. Vacuum leaks - allowing unmetered air to enter the engine. Very common in German cars such as BMW, Volkswagen and Mercedes-Benz.

How To Diagnose Engine Code P0101

For the purpose of this article, it’s assumed that you have a basic knowledge of safety precautions while working on your vehicle.

Always refer to the appropriate OEM literature when possible. Original manufacturer diagnostic procedures should always have precedence over a generic workflow.

That said, let’s start the diagnostic process!

1. Preliminary steps

To discard a possible intermittent DTC condition, you’ll need to clear the ECU memory and complete a driving cycle.

  • Read data trouble codes and take note of them.
  • Clear data trouble codes memory.
  • Perform a driving cycle (at least 5-10 minutes).

If the check engine light stays off then you may have an intermittent problem. If the light lit during your driving cycle then continue with the diagnostic process. It's not unusual to get other error codes along with P0101, these include P100, P0102, P0103, P0104, P0171, P0174 and P0299.

2. Visual Inspection

> Vacuum hoses: perform a meticulous visual inspection of all vacuum lines, including MAP sensor, PCV, brakes vacuum booster, fuel pressure regulator, etc. Also, check the air intake hose looking for any sign of deterioration or leak.

> MAF condition: to inspect the MAF condition you will need to remove it from the vehicle first. Be sure to check the MAF wiring after you unplug it from the sensor. Carefully check the condition of the MAF sensor inside the housing. You are looking for cracks in the sensor and excessive dirt that may be hindering its performance.

> Air Filter inspection: a clogged air filter could decrease the Turbocharger/Supercharger boost pressure significantly. Check the air filter condition and replace if necessary. 

Fix any wiring problem before continuing.

3. Electrical Tests

> MAF electrical tests: due to this sensor importance you should perform a comprehensive electrical test including continuity, reference voltage, ground, and supply voltage. Refer to our MAF article for detailed instructions about this procedure.

4. Scan Tool Tests

> Mass Air Flow Sensor live test: using an automotive diagnostic scanner you can perform a MAF “live test”. First, enter in KOEO mode and lock the MAF sensor related data on the display. Depending on your vehicle and scan tool maker you may have several items to check. Focus on the calculated MAF output, many times expressed in grams per second. You could also lock on screen the MAF output voltage if you can’t find it's calculated value.

Once you are ready to start the engine to enter KOER mode. If your scan tool has a graphing ability turn it on. Graph engine RPM and MAF output at the same time. Gently accelerate and decelerate the engine. The resulting lines should be similar, increasing and decreasing simultaneously. The greater the difference between them the greater the probability that you have a bad mass air flow sensor.


How To Repair Error Code P0101

Depending on the diagnostics results you may need to do the following:

  • Repair the MAF sensor wiring and/or connectors.
  • Clean the MAF sensor
  • Replace the MAF sensor
  • Replace the air filter
  • Repair vacuum leaks.