MAF circuit malfunction on Ford — contaminated or failed Hitachi/Bosch MAF sensor very common on TDCi/EcoBoost; rarely the wiring.
Ford P0100 — MAF circuit malfunction on Ford — contaminated or failed Hitachi/Bosch MAF sensor very common on TDCi/EcoBoost; rarely the wiring. Typical UK independent garage cost: £80–£280.
What actually causes P0100 on a Ford
Ford TDCi MAF sensors get oil-contaminated from blow-by gases routed through the breather — typical symptom is rough running, smoke under load and P0100. On 2.0 TDCi Galaxy/S-Max the MAF is reliably failed by 100k miles. On 1.0 EcoBoost the MAF is in the airbox lid and degrades slowly — engine still runs but fuel economy drops 5 MPG, triggering P0100 once readings drift far enough.
Ford engines that log P0100
- 1.6/2.0/2.2 TDCi (Mondeo, Focus, Galaxy, Transit)
- 1.0 EcoBoost (Fiesta, Focus, B-Max)
- 2.5T (Focus ST/RS)
How we diagnose P0100 on a Ford
- FORScan / IDS — read MAF g/s reading at idle and during snap throttle
- Inspect MAF for oil contamination (TDCi) — clean with MAF cleaner spray or replace
- Check airbox lid seal and air filter (a leaky airbox makes MAF read low)
- Inspect crankcase breather hose for oil pooling
- Replace MAF if readings stay drifted after cleaning
The common misdiagnosis to avoid
Avoid the dealer 'engine diagnostic' (£120+) on a high-mileage TDCi with P0100 — replacement MAF is £80–£140 and fixes it 90% of the time at first attempt.
Ford P0100 repair cost in the UK
Expect £80–£280 including parts and labour at an independent garage. Main-dealer quotes on Ford are usually higher for the same job, and the spread exists because the cheap cause and the expensive cause throw the same code — pay for the diagnosis before you pay for parts.
Bob's workshop tip
On Mondeo/Galaxy TDCi over 90k miles, just budget for the MAF as a routine maintenance item — it's not a question of if, it's when, and customer mood is better when warned in advance.
Codes usually seen alongside P0100 on Ford
- P0101
- P0102
- P0299
- P0401
Symptoms drivers report with P0100
- Black smoke on diesel acceleration (over-fuelling because ECU can't trust the airflow reading)
- Rough or 'hunting' idle at traffic lights — RPM wanders between 700 and 950
- Hesitation off the mark, then a sudden shove of power as the ECU falls back to a default air-map
- MPG drops 5–10 in mixed driving — the ECU can't run closed-loop trims without valid MAF data
- Engine surges at steady 50–60 mph motorway cruise
- Sometimes resets itself after key-off / key-on and drives normally for a day
- Often stored alongside P0101 (range) or P0102 (low input) — same root cause
Repairs that clear P0100
- Clean MAF with dedicated cleaner spray
- Replace MAF sensor
- Inspect wiring and connector
- Replace air filter
For the generic, all-makes explanation of this code — meaning, every known cause and UK cost bands — see our P0100 guide.