P0191

Fuel rail pressure sensor circuit range/performance.

Reported fuel-rail pressure did not match the range or response expected by the computer.

What should be checked

The module compares commanded pressure with reported pressure and monitors whether the signal remains within valid limits.

In plain language: The actual pressure, sensor reading or both may not coincide with what the computer requested.

How to check it: Compare commanded and measured pressure, and test the circuit only with equipment and limits appropriate for the exact system.
Before correcting it: Do not loosen lines or change sensor, pump, regulator or rail without a confirmatory test. The correction is decided only after locating and confirming the defect.
Related components: This diagnostic path may involve the pressure sensor, connector, wiring, pump, regulator, control valve, filter, or fuel rail. None is confirmed.
When to stop: High-pressure systems can cause serious injury; pressure testing and opening the system are tasks for trained personnel.

The quantity, pressure or fuel control may not match the engine's calculated demand.

In plain language: The engine may be receiving too much or too little fuel, but it still needs to be measured.

How to check it: Reviewing correction data and performing only the pressure or control tests indicated for the exact system.
Before correcting it: Do not open lines or replace injectors or pumps without a confirmatory measurement. The correction is decided only after locating and confirming the defect.
Related components: This path may involve fuel injectors, the pump, regulator, filter, lines, or their electrical controls. None has been confirmed.
When to stop: Fuel pressure, leakage, strong smell or smoke require immediate professional attention.

Choose the make and open its official portal to find the manual, diagrams, cylinder arrangement, and bulletins for the exact vehicle.

Availability, registration, and cost depend on the manufacturer. The link does not grant permission to copy the manual.

Understand which emissions-related service information manufacturers must make available for purchase.

Explains regulated access in the United States; it does not contain the vehicle-specific diagram or make the manual free.

Audi A3 Quick Reference Specification Book — Audi of America / archivo NHTSA. It supports the punctual definition of the code; It does not identify a cause, a part or a repair.
Frequently Asked Questions About On-Board Diagnostics — U.S. Environmental Protection Agency. Supports the safety difference between a fixed breakdown lamp and a flashing lamp; It doesn't diagnose the cause.