P0100Mass air flow (MAF) sensor circuit fault

Means the ECM sees a problem in the mass air flow circuit—not necessarily a dead sensor, but a path that will not report a believable airflow signal. On gasoline cars and light trucks the MAF sits in the intake tract after the air filter and tells the controller how much air is entering so injector pulse width and spark advance stay honest. When that signal drops out, sticks, or fights the MAP and throttle position correlation, you get a check-engine light, often with lean or rich trims, rough tip-in, and a readiness monitor that will not stay complete. Freeze frame usually captures a cruise or tip-in where calculated load and MAF grams-per-second disagree with what the throttle and rpm imply.

Treat P0100 as a circuit-and-plumbing code before you order a hot-film element. Shop frequency still starts with a contaminated or oil-soaked sensor element after an over-oiled aftermarket filter, then an open or high-resistance harness at the MAF connector, then a cracked, collapsed, or poorly clamped intake boot that lets unmetered air past the sensor. Wrong or loose ducting after a filter job is a classic “new filter, new code” pattern. Less often you chase a failed sensor heater, a short to power or ground on the signal wire, or an ECM input that only fails after the rest of the path ohms clean. Do not condemn the MAF because fuel trims are high: prove the signal first, then chase vacuum leaks that the MAF never sees.

Diagnosis is correlation, not parts roulette. Graph MAF g/s against rpm and throttle while the complaint is present; a flat line, dropout on bump, or reading that refuses to rise with tip-in is your first proof. Key-off ohm and voltage-test power, ground, and signal against the OEM chart; wiggle the harness at the snorkel and firewall while watching the PID. Smoke or carefully inspect the duct from filter to throttle body for tears at the bellows. Clean a serviceable hot-wire/hot-film element only with MAF-safe cleaner if the OEM allows it—never carb cleaner or shop towels. Replace the sensor when power/ground are good, ducting is sealed, and the live signal still fails OEM ramp checks. Dig elsewhere when a brand-new MAF still sets P0100 with a torn boot, when P0171/P0174 ride along with strong unmetered-air evidence, or when MAP and calculated load stay sane while only the MAF PID is nonsense. System context: MAF is the air half of closed-loop fueling; it commonly pairs with lean codes and can starve a catalyst monitor of a clean enable. Fix the metering path before you authorize injectors or a converter.