Draft guidance: awaiting Claude spot-check, qualified-mechanic review and named-editor approval. Do not use a fault code alone to replace parts.

P0191: Fuel rail pressure sensor “A” range/performance

The ECU receives a rail-pressure signal, but the reading is implausible or does not respond as expected.

What P0191 means

The ECU receives a rail-pressure signal, but the reading is implausible or does not respond as expected. The cause may be a biased sensor or electrical fault, or real fuel pressure that is too low, too high or slow to follow the requested value.

Can I still drive?

Arrange diagnosis promptly. A steady amber light with normal starting and performance may permit a short, gentle trip to a garage, but not a long journey. Stop and recover the car for hard starting, severe hesitation, limp mode, surging, stalling, a no-start, fuel smell or leakage, or too little power to join traffic safely.

Symptoms

  • Engine-management light.
  • Long cranking or no-start.
  • Weak acceleration, hesitation, surging or limp mode.
  • Rough running, stalling or no obvious symptom at first.

Common causes

  • Fuel-rail pressure sensor drift or internal failure.
  • Corroded connector, poor terminal contact or high-resistance wiring.
  • Low fuel level, restricted filter or restricted supply line.
  • Weak lift pump or high-pressure pump.
  • Faulty pressure-control/metering valve or regulator.
  • Excessive injector leak-back, a fuel leak or air entering the low-pressure side.
  • Less commonly, ECU/software or shared-reference trouble.

Safe first checks

  • Save all codes and freeze-frame data; a low-pressure, pump-supply or reference-voltage code may change the diagnostic route. Check the fuel level and whether the fuel filter is overdue. With the ignition off, inspect the sensor plug and nearby loom and look from a safe distance for wetness or damaged low-pressure hoses. A scan tool can compare requested and reported pressure, but the figures require vehicle-specific interpretation. Leave pressure gauges, injector leak-back tests and all rail opening to a qualified technician.

Typical UK fix cost

About £70–£160 for diagnosis. Connector, wiring or sensor work may total £100–£450; a fitted fuel filter may be around £90–£220. Genuine delivery faults can be much dearer: roughly £300–£800 for many low-pressure pump jobs, with high-pressure pump, control-valve or injector repairs potentially £700–£2,000+. Testing should justify expensive parts before replacement.

Related models

This is a generic OBD-II code used across many makes and models. The exact test thresholds, component layout and repair route vary by engine and manufacturer, so check vehicle-specific technical information before ordering parts.

Related fault codes

Sources

A diagnostic trouble code identifies a system or circuit to investigate. It does not prove that a named part has failed. Preserve freeze-frame data and seek a vehicle-specific diagnosis before clearing the code.