P0091
UniversalFuel Pressure Regulator Control Circuit Low
Medium SeverityThis code indicates that the Engine Control Module (ECM) has detected a low voltage condition in the control circuit for the fuel pressure regulator. A low voltage signal can prevent the fuel pressure regulator from functioning correctly, potentially leading to incorrect fuel pressure delivered to the engine and impacting engine performance.
⚠️ Before You Begin (Safety First)
Always disconnect the battery before working on electrical components. When dealing with the fuel system, ensure the engine is cool, relieve fuel pressure carefully, and be aware of the risk of fuel leaks or fire. Wear appropriate personal protective equipment.
Common Symptoms
- Check Engine Light illuminated
- Poor engine performance
- Reduced fuel economy
- Engine stumbling or hesitation
- Rough idling
- Engine may not start or may stall
Common Causes
- Faulty fuel pressure regulator
- Wiring harness open or shorted to ground in the control circuit
- Corroded or loose electrical connections
- Failed Fuel Pump Control Module (if applicable)
- Faulty Engine Control Module (ECM) (less common)
Frequently reported on: All Makes
Diagnostic Steps
- Visually inspect the wiring and connectors leading to the fuel pressure regulator for damage, corrosion, or loose connections.
- Check for proper voltage and ground at the fuel pressure regulator's control circuit using a multimeter, referencing your vehicle's service manual for specifications.
- If accessible, test the resistance of the fuel pressure regulator itself to ensure it's within specifications.
- If no wiring issues are found and the regulator tests fine, consider inspecting the Fuel Pump Control Module if your vehicle is equipped with one, as it often controls the regulator.
- Clear the code and test drive the vehicle to see if the code returns.
👨🔧 When to Call a Professional
If you have performed basic wiring checks and verified the fuel pressure regulator or its circuit components are visually sound but the code persists, it's time to consult a professional technician. Complex electrical diagnostics often require specialized tools and expertise.
Commonly Asked Questions
What does P0091 specifically mean?
It indicates that the vehicle's computer has detected a low voltage signal within the control circuit that operates the fuel pressure regulator.
Can I drive with a P0091 code?
While you might be able to drive, it's not recommended for long, as it can lead to poor engine performance, reduced fuel economy, and potential engine damage over time due to incorrect fuel pressure.
Is P0091 related to the fuel pump?
Not directly to the fuel pump itself, but the fuel pressure regulator works in conjunction with the fuel system to maintain correct pressure, so issues in its control circuit can indirectly affect overall fuel delivery.
How expensive is it to fix P0091?
Repair costs vary widely depending on the cause. A simple wiring repair might be inexpensive, while replacing a faulty fuel pressure regulator or an ECM could be more costly, ranging from $100 to $800+.
Where is the fuel pressure regulator located?
Its location varies by vehicle, but it's typically found on the fuel rail near the engine or integrated into the fuel pump assembly within the fuel tank.