What P0191 means
The rail pressure sensor A measures the pressure in the high-pressure fuel rail of common-rail diesels and gasoline direct-injection engines; it is either a three-wire sensor (5 V reference, ground, signal rising with pressure, about 0.5 V at 0 bar (0.0 psi)) or a digital SENT sensor with two measuring channels.
How the engine computer detects it
The engine module uses it as the feedback signal for rail pressure control. P0191 means the signal is electrically valid but not believable – stuck, offset or drifting. Manufacturers check it differently: Ford's 2023 diesels and GM's diesels test the offset with the system depressurized (Ford before starting after 10 min and 12 s after switch-off, window about 0.25–0.38 V; GM 6.5–14 % of supply); GM gasoline direct injection compares the two SENT channels (limit 1.0 MPa); Saab's V6 diesel flags a large target deviation while the signal barely moves. GM treats it as a one-trip fault. Ford gasoline direct injection uses P0087/P0088 instead. On a fault the module uses a substitute value and usually limits power.
Written from public technical sources and not yet checked by a mechanic. How we write these pages
Symptoms
- Check engine light on
- Limp mode or 'Reduced Engine Power'
- Hard starting, stalling
- Rough running
Common causes
- Rail pressure sensor drifting or stuck (wrong offset at 0 bar (0.0 psi)) Most likely
- Genuine pressure fault: high-pressure pump, pressure or volume control valve, tank pump Possible
- Connector corroded, contact resistance in signal or ground Possible
- Fuel shortage or clogged filter Less likely
- Control module software Less likely
How to diagnose P0191
- Read every stored code with an OBD-II scanner. If misfire or fuel trim codes are there too, fix those first: they often cause this one.
- Inspect the parts involved: fuel rail pressure sensor, sensor wiring, sensor reference voltage, high pressure fuel pump.
- Work through the causes above from most to least likely, cheapest checks first.
- Clear the code and drive a full drive cycle to confirm the repair held.
Vehicles that report P0191 most
| Vehicle | Years | Reports | Share | Median miles |
|---|---|---|---|---|
| Volkswagen Jetta | 2009–2010 | 5 | 62k | |
| Ford F-350 SD | 2021 | 3 | — | |
| Chevrolet Equinox | 2013–2023 | 3 | — |
Counts of owner complaints to the NHTSA that mention P0191 (29 in total), not failure rates: popular models get more complaints simply because more of them are on the road. Models with fewer than 3 complaints are left out.
Reading the code
- P
- Powertrain
- 0
- Generic (SAE) code
- 1
- Fuel and air metering
- 91
- Specific fault
Questions drivers ask
Can I drive with code P0191?
Drive gently and only as far as you need to. The engine computer may limit power to protect the engine, so avoid highways and heavy traffic until it's fixed. If the check engine light starts flashing, pull over.
Will my car pass an emissions inspection with P0191?
Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.
Can I fix P0191 myself?
Often yes, with an OBD-II scanner and basic tools. Difficulty: medium. Start with the cheapest checks before replacing expensive parts.
Often reported together
Codes that owners mention in the same NHTSA complaints as P0191. They can point to a shared cause, so it's worth checking them together.
This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.