The Quick Answer above is the generic definition. What follows is what is documented for the Ford models that log P0171, checked against manufacturer data and owner reports.
DTC/P0171·Ford
P0171 on Ford: Causes, Symptoms and Fix Cost
Quick Answer
Moderate SeveritySafe to drive (short-term)Ford
P0171 on a Ford means the air-fuel mixture on Bank 1 (the cylinder bank with cylinder 1) is too lean: too much air or too little fuel. The ECU keeps adding fuel to hit the 14.7:1 target ratio, but it has run out of room to compensate, so long-term fuel trim climbs past about +15% and the light comes on. The single most common cause is unmetered air entering after the airflow sensor, usually a vacuum or intake leak. Most fixes land between 100 and 350 EUR.
Repair cost on Ford€30 - €700
Connect any standard Bluetooth OBD2 adapter to your Ford and Skanyx tells you what P0171 means on that engine, whether it is safe to keep driving, and what the fix should cost. Free on iPhone and Android.
Get Skanyx freeWhat does P0171 mean on a Ford?
Ford Focus
2008-2024On the Focus, P0171 frequently traces to a dirty MAF sensor and to cracked or perished PCV and crankcase vent hoses, which are a known weak point on the 2.0L Duratec and the 1.0L EcoBoost. On the EcoBoost, also check the intake manifold and the charge pipe for splits, since a small boost leak leans the mixture and sets the code.
What causes P0171 on a Ford?
Beyond the generic causes listed on the main P0171 page, these are the documented Ford-specific patterns:
Ford FocusDirty MAF sensor underreporting airflow
Ford FocusCracked PCV and crankcase vent hoses on the 2.0L Duratec and 1.0L EcoBoost
How to diagnose P0171 on a Ford with OBD2
Follow these steps to pinpoint the root cause of P0171:
- Read short-term and long-term fuel trims with a scan tool. Long-term fuel trim above roughly +15% at idle confirms the lean condition, and if it improves at higher RPM the leak is unmetered air at idle
- Smoke-test the intake, or spray brake cleaner or carb cleaner around the intake manifold gasket, vacuum hoses, and PCV connections. A momentary RPM change pinpoints the leak
- Inspect and clean the MAF sensor with dedicated MAF cleaner, never touching the sensor element, then recheck fuel trims
- Check fuel pressure at the rail with a gauge and compare to the manufacturer specification, watching for pressure drop under load that points to a weak pump or clogged filter
- Inspect the PCV valve, oil separator, and their hoses for cracks, splits, or disconnection
- Check for an exhaust leak just before the upstream O2 sensor, which can fool the sensor into a false lean reading
- Compare Bank 1 and Bank 2 trims on V engines. If both banks read lean, suspect a shared cause such as the MAF, fuel supply, or a leak before the throttle body
How much does P0171 cost to fix on a Ford? (EUR)
Estimated repair costs for P0171 in EUR, compiled across makes. Ford costs typically sit in the middle of each range.
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
Related codes that often appear with P0171 on Ford
These codes commonly cluster with P0171 on Ford vehicles:
Looking for the full P0171 reference (all makes, full diagnosis flow, complete repair cost matrix)?
See the main P0171 guideSkanyx · Ford
Diagnose P0171 on your Ford
Your car logged P0171. Skanyx reads it on any standard Bluetooth OBD2 adapter, tells you whether it is safe to keep driving, and shows the €30-€700 repair range so you know the number before a shop quotes you. Free on iPhone and Android, and you do not need to be a mechanic to read it.
Get Skanyx free