P0100 - Mass Air Flow Circuit Malfunction

The mass air flow or MAF sensor is placed in the intake air duct between the air filter and the engine intake manifold. The MAF sensor measures the amount of intake air flow. The MAF sensor converts the air flow measurement into a voltage or frequency signal, with the voltage or frequency changing proportionally to the amount of the air flow. Read more about a mass air flow sensor.

The air flow sensor signal is monitored by the engine computer (ECM). The engine computer (ECM) uses the mass air flow signal to know the engine load and to calculate the proper amount of fuel injected. If the signal from the mass air flow sensor is out of expected range, the ECM detects a fault and sets the code P0100.

Symptoms:

A car with the code P0100 may have some driveability issues, such as stalling, lack of power, surging, hesitation, etc. In some cars, the code P0100 can cause the fail-safe mode where the engine speed would be limited to 2,500 - 3,000 rpm.

Causes:

- faulty or contaminated mass air flow sensor
- open or short in the mass air flow sensor electrical circuit
- other electrical problem with the MAF sensor wiring, (corroded wires, bent terminals, bad ground connection, burned fuse, etc.
- vacuum leaks
- restricted air flow (clogged up air screen, gummed up air intake, clogged up catalytic converter, etc.)
- air filter box not closed properly
- wrong air flow sensor installed
- problem with the ECM

How the code P0101 is diagnosed:

If there are other trouble codes present, they might need to be looked at first. Checking the freeze frame may help, as it may contain some important information. The freeze frame is a snapshot of the engine parameters at the moment when the fault was detected. The freeze-frame may show whether the vehicle was running or stopped, whether the air–fuel ratio was lean or rich, was the engine was cold or warmed up at the time of the malfunction. First, The MAF sensor connector and the wiring between the mass air flow sensor and the ECM must be checked for open or short, loose terminals, corrosion or damage. The mass air flow reference voltage and ground must be checked at the sensor connector.

An air duct between the mass air flow sensor and the engine intake needs to be checked for cracks, tears, loose clamps or improper connection. The air filter element needs to be checked and replaced if very dirty. The engine needs to be checked for vacuum leaks. Read more: Vacuum leaks: common sources, symptoms, repairs

A mass air flow sensor signal must be checked with a voltmeter or better with a scan tool at different RPMs and compared to the reference chart or values from a known good mass air flow sensor.

In many cases, if no other issues found, the mass air flow sensor may need to be replaced. In some vehicles (e.g. Nissan), when the new air flow sensor is installed, the fuel trim learned value must be reset.

A new mass air flow sensor may cost from $70 to $350. Replacing the MAF sensor is an easy task and won't be expensive in an auto repair shop. We recommend using an original (OEM) part, as an incorrect MAF sensor also could cause problems. If the problem is fixed, the code P0100 will clear itself after driving.

Examples

We found several reports, where a bad MAF sensor ground connection has caused the code P0100 along with some other codes. This happens in different cars, including Toyota, Opel and other brands.

In some Volkswagen cars, the code P0100 could be caused by a broken wire in the MAF sensor harness. This post provides an example.

In some older Toyota trucks, Subaru and Nissan vehicles (e.g. Nissan Maxima, Frontier, Sentra, Pathfinder, as well as Infinity Q30, QX4) the code P0100 could be caused by a bad mass air flow sensor or broken soldering at mass air flow sensor terminals. Sometimes this problem may also cause intermittent issues, like stalling or stumbling.

A Nissan technical service bulletin (TSB) for 2000-2001 Maxima describes another problem where the mass air flow sensor could be damaged by dust/dirt causing the code P0100. As a solution, Nissan recommends cleaning the air filter housing, replacing the mass air flow sensor assembly and installing the original Nissan air filter, as well as checking, and if needed, reprogramming the ECM.

In some Volkswagen, BMW and Mercedes-Benz cars, the code P0100 could also be caused by a bad MAF sensor. The MAF sensor needs to be checked and replaced if needed. See, for example, this post.