P0100: Mass or Volume Air Flow Sensor A Circuit
What to do
Usually driveable but noticeably poorer: hesitation, worse economy, sometimes a rough idle. Worth attending to promptly, since the module is guessing at fuelling until it is fixed.
What this code means
A circuit fault in the mass air flow sensor — the device that tells the engine control module how much air is actually entering the engine. Almost every fuelling decision starts from this number, so losing it forces the module onto a calculated estimate derived from throttle position and engine speed. The engine will usually still run on that estimate, but it runs approximately rather than accurately.
Likely causes
Start here
- Contaminated or failing mass air flow sensor · easy
- Corroded or loose connector · easy
- Open circuit in sensor wiring · moderate
Less common
Rare
- Failed control module · specialist
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
Be the first to write this up
Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.
What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
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