P0191 code meaning
Fuel Rail Pressure Sensor A Circuit Range/Performance
Powertrain system Generic code P01xx codes Check engine light
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) or a digital SENT sensor with two measuring channels. 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 depressurised (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.
P0191 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P0191
- Check engine light on
- Limp mode or 'Reduced Engine Power'
- Hard starting, stalling
- Rough running
Common causes of P0191
- Most likelyRail pressure sensor drifting or stuck (wrong offset at 0 bar)
- PossibleGenuine pressure fault: high-pressure pump, pressure or volume control valve, tank pump
- PossibleConnector corroded, contact resistance in signal or ground
- Less likelyFuel shortage or clogged filter
- Less likelyControl module software
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Fuel rail pressure sensorSensor wiringSensor reference voltageHigh pressure fuel pump
What each part of P0191 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 1 | Area: fuel and air metering. |
| 91 | The exact fault in that area. |
What to do next
- Note P0191 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0191
What does P0191 mean?
P0191 means "Fuel Rail Pressure Sensor A Circuit Range/Performance". 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) or a digital SENT sensor with two measuring channels. It is a generic code, so it means the same on every make.
Is it safe to drive with P0191?
Drive gently and only to a workshop. With P0191 the car can go into limp mode (reduced power) to protect itself.
Will P0191 fail an emissions test?
Yes, it can. P0191 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0191 to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P0191 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.