The rail pressure sensor A measures the pressure in the high-pressure fuel rail of common-rail diesels and petrol 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 petrol 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 petrol direct injection uses P0087/P0088 instead. On a fault the module uses a substitute value and usually limits power.
High severity. Can I keep driving?Do not continue your trip: you could lose power on the road or stall when braking. If the problem is a pump shedding metal particles, driving spreads the damage to the rest of the system.
Symptoms
- Check engine light on
- Limp mode or 'Reduced Engine Power'
- Hard starting, stalling
- Rough running
Most likely causes
- Rail pressure sensor drifting or stuck (wrong offset at 0 bar)
- Genuine pressure fault: high-pressure pump, pressure or volume control valve, tank pump
- Connector corroded, contact resistance in signal or ground
- Fuel shortage or clogged filter
- Control module software
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: medium
- It can trigger limp mode.
- It affects emissions.
What each character of P0191 means
- P: Powertrain: engine and transmission
- 0: Generic code: same on every make
- 1: Air and fuel
- 91: Specific fault in that system
Frequently asked questions
Can I keep driving with code P0191?
Do not continue your trip: you could lose power on the road or stall when braking. If the problem is a pump shedding metal particles, driving spreads the damage to the rest of the system.
What causes code P0191?
The most common causes are: rail pressure sensor drifting or stuck (wrong offset at 0 bar); genuine pressure fault: high-pressure pump, pressure or volume control valve, tank pump; connector corroded, contact resistance in signal or ground.
Related codes
- P0190Fuel Rail Pressure Sensor A Circuit
- P0192Fuel Rail Pressure Sensor A Circuit Low
- P0193Fuel Rail Pressure Sensor A Circuit High
- P0194Fuel Rail Pressure Sensor A Circuit Intermittent/Erratic
- P0087Fuel Rail/System Pressure - Too Low
- P01BFFuel Rail Pressure Sensor Circuit Range/Performance Bank 2
Sources
- law.cornell.edu: 13 CCR 1968.2
- fordservicecontent.com: obd summary diesel 2023
- gsi.ext.gm.com: 18OBDG04 Engine Diagnostics
- gsi.ext.gm.com: 18OBDG03A Engine Diagnostics
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.