DTC P0091 – Fuel Pressure Regulator 1 Control Circuit Low

Meaning

P0091 indicates that the ECM/PCM detects low voltage in the control circuit of Fuel Pressure Regulator 1 (usually a fuel rail pressure control actuator or pressure regulating control valve in common rail systems).

Common Symptoms

Hard starting (especially cold)

Low engine power

• Engine stalling or hesitation

Rough idle

MIL/Check engine light ON

Poor acceleration

Possible Causes

Electrical

Open/short to ground in fuel pressure regulator control circuit

Corroded, damaged, loose connector at regulator

Damaged wiring harness near engine/rail

Poor ground or battery voltage issue

Faulty fuel pressure regulator (electronic)

Mechanical / Fuel System

Low fuel pressure (pump weak)

Blocked fuel filter

Faulty fuel rail pressure sensor sending wrong data

Fuel leaks

ECM failure (rare)

Component Location

Fuel Pressure Regulator 1 is normally:

Mounted on the high-pressure fuel pump (some vehicles)

Installed on the fuel rail (common rail diesel systems)

Quick Checks in Workshop

🌟 1. Visual inspection

Check wiring for damage, cuts, oil contamination, connector looseness

Check regulator connector pins for corrosion

🌟 2. Electrical Testing (Multimeter)

Regulator Connector

Signal/control wire should show: 5–12V (key ON depending on system)

Ground should have continuity

If 0V or very low voltage, circuit is shorted to ground or ECM driver is faulty.

🌟 3. Fuel Pressure Check

Using scan tool:

Compare desired pressure vs actual pressure
If actual pressure is too low → pump/filter issue, not electrical.

🌟 4. Actuator Test

Use scan tool to:

Activate Fuel Pressure Regulator

If no response → regulator is faulty or wiring open

🌟 5. Check Fuel Filter

A clogged filter causes low pressure → ECM increases duty cycle → may trigger code.

Voltage/Resistance Expected Values (generic, varies by manufacturer)

Regulator coil: 2–6 Ω

Control circuit: 5–12V

Ground: <0.1 Ω

(If you give vehicle model/engine, I will give exact values.)

Common Fixes

Repair damaged wiring

Clean/replace corroded connector

Replace fuel pressure regulator

Replace fuel filter

Repair/replace fuel pump (if low pressure)

Replace fuel pressure sensor (if readings inconsistent)

ECM repair (rare)

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