Mass or Volume Air Flow Circuit Malfunction
Our emissions expert has put together the following information about the P0100 fault code. We have also included diagnostic procedures you can take to your repair shop if the mechanic is having difficulty analyzing the code.
OBD II Fault Code
- OBD II P0100
Fault Code Definition
- Mass Air Flow Circuit Malfunction
- Check Engine Light will illuminate
- Engine runs poorly
- Vehilce may stall and/or hesitate on acceleration
- Poor fuel mileage
- In some cases, no abnormal symptoms may be noticed
Common Problems That Trigger the P0100 Code
- The MAF Sensor is unplugged or the wiring is damaged
- Loose or corroded electrical terminals in the MAF Sensor circuit
- Faulty MAF Sensor
- MAF Sensor replaced when the cause of code P0100 is a defective connector and/or wiring harness
- MAF Sensor replaced when the cause of code P0100 is a vacuum leak
- MAF Sensor replaced when the cause of code P0100 is a misfiring engine
Polluting Gases Expelled
- HCs (Hydrocarbons): Unburned droplets of raw fuel that smell, affect breathing, and contribute to smog
- CO (Carbon Monoxide): Partially burned fuel that is an odorless and deadly poisonous gas
- NOX (Oxides of Nitrogen): One of the two ingredients that, when exposed to sunlight, cause smog
P0100 Diagnostic Theory for Shops and Technicians
When diagnosing a P0100 code, it is important to record the freeze frame information and then to duplicate the code setting conditions with a test drive. Pay close attention to the engine load, throttle position, RPM, and road speed. Compare these values to the Mass Air Flow grams per second PID. If the grams per second varies a lot or moves in opposite directions to RPM and throttle position, then you may have verified the P0100 code setting condition.
There is a very effective "truth test" for any Mass Air Flow Sensor. Start the engine, let it idle, and then check the Barometric Pressure reading on the scan tool data. Say the reading is 26.5 Hg and you are close to sea level, you know that you have a defective Air Flow Meter because it is telling you that you are at about 4500 feet above sea level. (These conversion tables will help.) When the Mass Air Flow Sensor sees this Barometric reading, it adjusts its Air Density table and then "under reports" the actual amount of air entering the engine. It does this because the Barometric Pressure Sensor is actually part of the Mass Air Flow Sensor.
Sometimes the Air Flow Sensor and the sensing wire get covered with dirt, dust, or oil residue, which can set a P0171 in addition to the P0100 code. Cleaning the sensor might hold off problems for a while, but the MAF sensor should be replaced. This is due to the fact that cleaning the wire isn't a thorough enough solution. A microscopic view of the wire will show that that 50% or more of the contamination is embedded into the sensing wire's grooves and crevices. Always make sure the Air Filter and its enclosure are dirt-, dust-, and oil-free. If you clean and replace the filter and its enclosure as needed, you will prevent the new MAF from failing.