P0091: Fuel Pressure Regulator 1 Control Circuit Low

What does P0091 mean?

The monitored control circuit for fuel pressure regulator 1 is below its expected electrical limit. The number 1 identifies a regulator circuit, not cylinder 1 or necessarily the first pump on the vehicle.

Generic OBD-II definition: Fuel Pressure Regulator 1 Control Circuit Low. Confirm applicability in your vehicle service information.

Common causes

• Control circuit shorted to ground
• Failed regulator solenoid
• Supply or connector fault

Symptoms

• Difficult starting
• Reduced power
• Rough running or check engine light

Diagnostic focus

Do not equate control-circuit low with low rail pressure. The computer may command a fail-safe response that changes pressure in either direction depending on system design.

Can I keep driving with P0091?

Severity: High Avoid driving if the engine stalls, leaks fuel, or runs roughly. High-pressure fuel testing belongs with a qualified technician; never loosen a fuel rail or injector pipe to check pressure.

If the check engine light is flashing or the car runs badly, stop driving and have it checked.

Typical fixes

• Inspect the regulator wiring for heat damage and corrosion
• Test the feed and control circuit, checking for shorts to ground without jumpering the valve.
• Repair the verified wiring fault or replace a regulator that fails testing

Sources & review

• OBD-Codes.com: P0091
• TroubleCodes.net: generic code definitions

Definitions and diagnostic background checked 2026-11-06. Generic guidance, not a substitute for the service procedure for your exact year, engine, and transmission.