P0191 means Fuel Rail Pressure Sensor A Circuit Range/Performance. The fuel rail pressure sensor reading does not make sense for current conditions, or does not change as expected. It is a generic OBD-II code, so the definition is the same on any make, but the most likely cause varies by engine; confirm with a scan tool and the service information for your vehicle before buying parts.
What P0191 means
Modern engines measure boost and fuel rail pressure and compare them with a desired value calculated from engine speed, load and throttle. When actual pressure falls short of desired for long enough, the computer sets a code and often reduces power to protect the engine. Watching desired and actual values side by side on a scan tool shows whether the shortfall is constant or only appears under load.
P0191 symptoms
- Hard starting or long cranking
- Loss of power or reduced-power mode
- Stalling
Common causes of P0191
- Failing rail pressure sensor
- Wiring or connector problems
- Real pressure problems from a weak pump or clogged filter
How to diagnose P0191
- Check key-on, engine-off rail pressure (it should read close to zero on many diesels after sitting)
- Inspect the sensor connector and wiring
- Compare readings with a mechanical gauge where possible
Can you drive with P0191?
Not reliably; stalling and no-starts are common.
P0191 tips
With the engine off and sitting, rail pressure should bleed down; a sensor that still reads high pressure with the engine off is likely faulty. Compare its reading with a mechanical gauge where the system allows.
Will P0191 clear itself?
If the fault stops, the computer turns off the check engine light by itself after several drive cycles without seeing it again, and the code stays in memory as history for a while. Clearing P0191 with a scan tool after a repair is fine, but if the cause is still there the code returns, sometimes within one drive. Disconnecting the battery also clears codes on most vehicles, but it erases learned fuel trims and idle settings as well.
Related codes
| Code | Meaning |
|---|---|
| P0193 | Fuel Rail Pressure Sensor A Circuit High |
| P0087 | Fuel Rail/System Pressure Too Low |
| P0088 | Fuel Rail/System Pressure Too High |
Guides that help
When it is more than a sensor
Our superchargers page lists supercharger kits, and diesel owners can read the 6.7 Cummins turbo guide. If a failed turbo or fuel pump has damaged the engine, compare engines by code on our engines page.
Shipping is a flat $80.00 per order to US addresses, with 15-day free returns. Questions? Ask a parts specialist.