P0100

P0100 indicates an electrical fault in the Mass Air Flow sensor circuit itself — the ECM is not seeing a coherent signal on the MAF signal wire, distinct from P0101 which says the signal is present but implausible. Cheapest-first ladder: unplug the MAF connector and inspect for green corrosion or pushed-back pins (5 minutes, free); back-probe the 5V reference with a DMM key-on engine-off and confirm 4.9-5.1V, then check the ground reference (should be under 0.1V drop to battery negative); with engine running at idle, the signal wire on a digital MAF should show a frequency between 2.0-4.5 kHz on a 2.4L four-cylinder and 3.5-6.0 kHz on a 5.7L V8, while an analog MAF idles around 0.7-1.1V and climbs to 4.0-4.5V at WOT; airflow at warm idle should read roughly 3-5 g/s on a 2.4L, 6-9 g/s on a 5.7L V8, and 25-35 g/s near WOT on the same V8. Do not throw a $250 MAF at a P0100 before you have ruled out a chafed harness against the valve cover or a corroded ECM pin — both are common and a new sensor will set the code again within minutes.

Vehicle-specific patterns: 2004-2008 Ford F-150 5.4L 3V routinely chafes the MAF harness where it crosses the passenger valve cover, setting P0100 intermittently after engine warm-up; 2007-2014 GM 5.3L trucks throw P0100 when the MAF connector locking tab breaks and the plug walks loose over speed bumps; 2003-2007 Honda Accord/Odyssey J-series sees P0100 from a cracked solder joint inside the MAF itself, not a wiring fault, and the sensor must be replaced; 2008-2012 VW/Audi 2.0T (BPY, CCTA) sees P0100 from rodent-chewed insulation under the engine cover where the MAF harness crosses the airbox. Estimated repair: $35 to $450.