OBD-II · Engine and powertrain (P)
P0191
Fuel rail pressure sensor range/performance
What it means
Rail pressure readings do not match requested pressure or engine load.
Symptoms
- reduced power or limp mode
- hesitation, jerking or misfire under load
- long cranking or hard starting
- engine may stall
- engine warning light
Likely causes, most likely first
| No. | Cause |
|---|---|
| 01 | faulty rail pressure sensor |
| 02 | weak low-pressure fuel supply or clogged filter |
| 03 | worn high-pressure pump |
| 04 | pressure regulator or volume control valve fault |
| 05 | excessive injector leak-off (diesels) |
What to check, step by step
- 01Read requested and actual rail pressure and freeze-frame data. Evaluate engine-off pressure against the specified pressure-decay time; residual pressure can remain after shutdown.
- 02Check the sensor connector, 5 V reference and ground
- 03Check the low-pressure supply and fuel filter
- 04Validate the rail sensor electrically using OEM data; any independent high-pressure measurement requires specified, pressure-rated workshop equipment. Depressurise as specified before opening the system; never use an ordinary fuel-pressure gauge on the high-pressure rail.