P0191 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 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.
Likely causes
Symptoms
- Check engine light on
- Limp mode or 'Reduced Engine Power'
- Hard starting, stalling
- Rough running
Repair estimate
Typical range across vehicles; the real cost depends on what the testing finds.
What to check first
- Compare desired and actual pressure
- Check low-side supply
- Inspect sensor wiring
Parts involved
Related codes
References: law.cornell.edu, fordservicecontent.com, gsi.ext.gm.com, gsi.ext.gm.com.