P0101 - Mass Air Flow Sensor Circuit Range/Performance

Common problems causing the code P0101 in different cars:

In some GM and Chevy cars and trucks, the code P0101 could be caused by a clogged up catalytic converter. A clogged up catalytic converter can be verified by measuring the intake vacuum and the exhaust backpressure. Accompanied symptoms may include misfiring codes P0300 to P0308, lack of power under heavy load or on acceleration, overheating of the catalytic converter and poor gas mileage. A catalytic converter should be covered by the emission warranty (typically 8 years or 80K miles)

Another issue in some GM trucks is leaking intake gaskets. One of the symptoms of a leaking intake gasket is the engine running rough when started cold.

In vehicles with an oil-soaked aftermarket air filter, oil from the air filter can contaminate the MAF sensor element, causing the code P0101 or other MAF-related codes.

In some Volvo cars, the code P0101 could be caused by a dirty throttle body or vacuum leaks in the PCV system (e.g. vacuum line to the oil separator). A dirty throttle body will need to be cleaned and the intake will have to be tested for vacuum leaks.

A technical service bulletin for some 2011-2012 Nissan Altima, Maxima and Sentra models recommends reprogramming the ECM (engine computer) if the code P0101 is stored and there are no driveability concerns.

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How the code P0101 is set

The code P0101 means that the signal from the mass air flow sensor (MAF) is out of expected range. The MAF sensor is installed in the engine intake, right after the air filter. it measures the amount of air entering the engine through the throttle valve. The engine computer (PCM) uses the signal from the MAF sensor for operating the fuel injection system. When the car is accelerated, the throttle valve opens and allows more air to flow into the engine. The MAF sensor detects the air flow and sends the signal to the engine computer, which in turn commands the fuel injection system to add more fuel. Similarly, when low air flow is detected, the PCM reduces the fuel supply.

Chevrolet MAF sensor
Chevrolet Cruze MAF sensor

The PCM checks the rationality of the MAF sensor signal by comparing it to the signals from the intake air temperature sensor (IAT), manifold absolute pressure sensor (MAP), throttle position sensor (TPS) and some others. If the signal from the MAF sensor is lower or higher than expected, the ECM detects a fault and stores the code P0101 in its memory. In many cars the MAF signal is used to determine the shift pattern of the automatic transmission. Often, if there is a problem with the MAF sensor, the automatic transmission may shift differently. If the MAF sensor is bad, replacing it with an OEM part will insure that further problems won't be caused by an incorrect part.

Q: 2004 Chevy Astro van feels sluggish at more than half throttle; ran the diagnostic, the codes P0101 and P0300 came up. What could cause this?

A: Check the short and long fuel trims and MAF sensor readings with a scan tool at different RPMs. Check the throttle body and clean it if it's dirty. Check and if needed, clean the MAF sensor. Check the MAF sensor harness and connector for poor connection or damage. Have the exhaust backpressure tested for a plugged catalytic converter; this is a common problem.

Q: 2001 Volvo with the code P0101. Could not find any vacuum leaks; the MAF sensor looks clean, what else could cause this code?

A: Check the throttle body, if it's dirty, clean it. Check the connectors and the wiring at the MAF sensor. If you have a scan tool, look at the short fuel trim numbers at high and low RPMs. If the short fuel trim (STFT) goes lean at low RPMs, it's a sign of a vacuum leak. A leaking purge valve, as well as brake vacuum booster can also cause this problem. Check the MAP sensor; it's used to check for rationality of the MAF sensor. If the MAP sensor is faulty, it also can cause the code P0101.

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