P0091: 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 solenoid regulates fuel pressure by controlling the amount of fuel returning to the tank. A low voltage signal suggests a short to ground, open circuit, or faulty component in the circuit, which can lead to improper fuel pressure regulation and affect engine performance.
01. Most Common Causes
- Faulty fuel pressure regulator solenoid
- Short to ground in the control circuit wiring
- Open circuit in the control circuit wiring
- Corroded or damaged connector at the solenoid
- Failed ECM (rare)
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Engine may run rich or lean, causing rough idle or hesitation
- Decreased fuel economy
- Possible hard starting or stalling
03. Step-by-Step Diagnosis
Step 1: Use a scan tool to confirm P0091 and check for related codes.
Step 2: Visually inspect the fuel pressure regulator solenoid connector and wiring for damage, corrosion, or loose connections.
Step 3: Using a multimeter, check the solenoid resistance (typically 4-12 ohms) and compare to specs.
Step 4: Check for voltage at the solenoid connector with key on; should be battery voltage. If not, test the circuit for opens/shorts.
Step 5: If circuit and solenoid are good, test the ECM output or replace the ECM as last resort.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances as improper fuel pressure can cause engine performance issues and potential damage to the catalytic converter or engine.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for parts and labor, depending on whether it's a simple wiring repair or solenoid replacement.