P0191
Fuel Rail Pressure Sensor Circuit Range / Performance
The fuel rail pressure sensor signal is within electrical limits but doesn't match commanded rail pressure under various engine loads. Common in common-rail diesel and GDI petrol engines.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: hard
What we see in the workshop
ON FORD ECOBOOST
Rail pressure sensor range faults on EcoBoost engines are worth logging live before replacement — a failing high-pressure pump can report the same way.
Common causes
Ordered by how often each turns out to be the cause.
- Pressure sensor driftedCommon
- Pressure regulator stuckPossible
- High-pressure pump wornLess likely
Parts involved
- Fuel Rail Pressure Sensor
- High Pressure Pump
- Rail Pressure Regulator
P0191 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.