P0191: rail-pressure sensor circuit range/performance; check feedback and wiring before replacing parts.
Meaning, symptoms, causes and checks
Rail-pressure feedback is implausible for the monitored conditions. Measurement or actual-pressure problems may be involved; this does not automatically condemn the sensor.
Affected system: Powertrain
Symptoms
- Engine warning lamp; possible protective operation.
- Hard starting, reduced power or stalling depending on fallback strategy.
Possible causes
- Corroded connector, loose terminal or damaged sensor wiring.
- Incorrect actual pressure from supply/regulation, or biased sensor response.
What to check
- Identify sensor and bank using engine documentation; check related supply/reference codes.
- Save failure data and monitor reported pressure; determine whether the fault occurs at key-on, starting or load.
- Inspect sensor connector, wiring and terminal retention; do not remove a sensor from a pressurized rail. For GM L5P/L5D check 20-NA-197 applicability.
- Compare requested/reported pressure at starting and under failure conditions; validate actual pressure only with OEM-approved equipment/methods.
- After repair recheck feedback under the same conditions; sensor/pump replacement depends on results.
Also written as: P0191-00, P019100, PO191 (some scan tools add the fault-type byte, e.g. -00).