P0101 - Mass Air Flow Sensor Circuit Range/Performance
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 intake air duct between the engine air filter and the throttle body; it measures the amount of air entering the engine through the throttle valve. The engine computer (ECM) uses the signal from the MAF sensor for operating the fuel injection system. When the car is accelerated, the throttle valve opens and more air flows into the engine. The MAF sensor detects the air flow and sends the signal to the ECM; the ECM commands fuel injection system to add more fuel. Similarly, when low air flow is detected, the ECM reduces the fuel supply.
Mass air flow sensor (MAF)
The ECM 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. The code P0101 could be caused by a number of problems, but the MAF sensor is usually the first suspect. Check the freeze frame, as it can contain some valuable information. The MAF sensor can be checked with a scan tool, by checking the mass air flow readings at different engine rpms and comparing to what is specified. 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.
- faulty or contaminated MAF sensor
- dirty throttle body
- unmetered air past the MAF sensor (vacuum leaks) from tears or cracks in the intake air duct (boot), faulty PCV valve, cracked vacuum hoses, loose intake air duct clamps, etc.
- blocked catalytic converter
- bad or dirty manifold absolute pressure sensor (MAP)
- electrical problems with the MAF sensor connector or wiring
- stuck open EGR valve
- incorrect valve timing
- faulty engine computer (ECM)
In some GM cars and trucks, the code P0101 could be caused by a plugged catalytic converter. A plugged catalytic converter can be verified by measuring the exhaust backpressure. Accompanied symptoms may include, sluggish acceleration, random misfiring with the codes P0300 to p0308 and lack of power.
In some vehicles with the oil soaked aftermarket air filter installed, 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; if this is the case, the throttle body needs to be cleaned.
What to check:
If you have an oil soaked air filter, check the MAF sensor for contamination. Check the air filter and the screen in the duct before the air filter for restrictions. Checking the MAF sensor readings at different rpms with a scan tool can help pinpoint a faulty MAF sensor. The reading and the voltage of the manifold absolute pressure (MAP) sensor also need to be checked, as if it doesn't work properly, it can cause a MAF fault with the code P0101. Check the throttle body; if it's dirty, cleaning it will be a good start. Vacuum leaks will cause unmetered air to enter the intake past the MAF sensor, which can also cause the code P0101. An intake duct from the air filter to the engine intake needs to be checked for vacuum leaks caused by loose clamps, tears or cracks; this type of problems is common in many European vehicles, e.g. BMW, Volvo. Other vacuum hoses also need to be checked for vacuum leaks. The PCV valve needs to be checked. In some vehicles, the ECM may need to be reprogrammed.
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.
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.