Fuel Pressure Regulator 1 Control Circuit Low
The P0091 code means the vehicle's onboard diagnostic system has detected: Fuel Pressure Regulator 1 Control Circuit Low. This is a critical severity code.
- Keep driving?
- No -- stop driving
- DIY difficulty
- hard
- Estimated cost
- $150 - $600 (parts and labor)
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Common Symptoms
- Check Engine Light on
- Hard starting or no start
- Engine stalls at idle
- Black smoke from exhaust (over-fueling)
Probable Causes (Ranked by Likelihood)
- Short to ground in fuel pressure regulator wiring Very High
- Internally shorted regulator solenoid High
- Corroded connector at fuel rail Moderate
- PCM driver circuit shorted Low
Step-by-Step Diagnostic Procedure
-
Measure fuel pressure regulator solenoid resistance. Below spec indicates internal short.
-
Check wiring for short to ground, especially near fuel rail where fuel leaks can damage insulation.
-
Disconnect solenoid and verify scan tool reading changes to indicate open circuit.
-
Inspect fuel rail connector for fuel contamination or corrosion.
Frequently Asked Questions
What does circuit low mean on P0091?
Circuit low means the PCM detects a lower voltage than expected on the fuel pressure regulator circuit. This usually indicates a short to ground in the wiring or solenoid.
Can P0091 cause engine damage?
Yes, if the regulator is stuck causing excessive fuel pressure, it can damage injectors. If pressure is too low, lean conditions can damage pistons and catalytic converters.
Should I replace the fuel pressure regulator for P0091?
Not immediately. First verify the wiring is intact. A shorted wire will damage a new regulator. Test the solenoid resistance and wiring before replacing parts.
Sources
This page is built from documented references. Verify against your own service info before repair work.
P0091 on Diesel, EV & Equipment
The same code ID appears across other engines and platforms. The diagnostic flow varies by manufacturer — these are the platform-specific breakdowns:
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