Fuel Pressure Regulator 1 Control Circuit Low
The P0091 code indicates that the Engine Control Module (ECM) has detected a low voltage condition in the control circuit of the fuel pressure regulator solenoid. This regulator is typically part of the high-pressure fuel system on direct injection engines. The ECM commands the regulator to maintain proper fuel pressure; a low circuit voltage suggests a short to ground, open circuit, or faulty regulator, which can disrupt fuel pressure regulation and engine performance.
1. Most Common Causes
- Faulty fuel pressure regulator solenoid
- Short to ground in the control circuit wiring
- Open circuit in the control circuit wiring
- Damaged connector or poor electrical connection
- Failed ECM (rare)
2. Symptoms You Will Notice
- Check Engine Light illuminated
- Engine may run rough or misfire
- Reduced engine power or hesitation
- Poor fuel economy
- Hard starting or stalling
3. Step-by-Step Diagnosis
Step 1: Scan for additional codes and freeze frame data to understand conditions when code set.
Step 2: Visually inspect the fuel pressure regulator connector and wiring for damage, corrosion, or loose connections.
Step 3: Use a multimeter to check the control circuit voltage at the regulator connector with key on, engine off; should see battery voltage (12V) or a PWM signal depending on system.
Step 4: Check for continuity to ground and power; if short to ground is found, repair wiring. If open, trace and repair.
Step 5: If wiring is intact, test the regulator solenoid resistance (typically 4-12 ohms) and compare to specs; replace if out of range.
Step 6: Clear codes and test drive; if code returns, consider ECM failure (rare).
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive with this code as it can cause poor engine performance, stalling, or damage to the fuel system. Have it diagnosed and repaired promptly.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for parts and labor, depending on the cause. A simple wiring repair may be on the lower end, while replacing the fuel pressure regulator can be higher.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.