P0091 means Fuel Pressure Regulator 1 Control Circuit Low. The fuel pressure regulator 1 control circuit voltage is lower than expected, as if shorted to ground. It is a generic OBD-II code, so the definition is the same on any make, but the most likely cause varies by engine; confirm with a scan tool and the service information for your vehicle before buying parts.
What P0091 means
Modern engines measure boost and fuel rail pressure and compare them with a desired value calculated from engine speed, load and throttle. When actual pressure falls short of desired for long enough, the computer sets a code and often reduces power to protect the engine. Watching desired and actual values side by side on a scan tool shows whether the shortfall is constant or only appears under load.
P0091 symptoms
- Check engine light
- Hard starting or stalling
- Loss of power or reduced-power mode
Common causes of P0091
- Wiring shorted to ground
- Failed regulator
- Damaged connector
How to diagnose P0091
- Check the regulator’s connector and wiring
- Watch desired vs actual rail pressure on a scan tool
- Check the fuel filter and lift pump supply
- Look for external leaks
Can you drive with P0091?
Short distances only; the engine may stall or limit power.
P0091 tips
A low-circuit code points to a short to ground in the regulator wiring; look for chafing where the harness passes near brackets. Unplugging the regulator and checking the circuit with a meter separates a wiring fault from a failed regulator before you buy parts.
Will P0091 clear itself?
If the fault stops, the computer turns off the check engine light by itself after several drive cycles without seeing it again, and the code stays in memory as history for a while. Clearing P0091 with a scan tool after a repair is fine, but if the cause is still there the code returns, sometimes within one drive. Disconnecting the battery also clears codes on most vehicles, but it erases learned fuel trims and idle settings as well.
Related codes
| Code | Meaning |
|---|---|
| P0090 | Fuel Pressure Regulator 1 Control Circuit |
| P0092 | Fuel Pressure Regulator 1 Control Circuit High |
| P0087 | Fuel Rail/System Pressure Too Low |
Guides that help
When it is more than a sensor
Our superchargers page lists supercharger kits, and diesel owners can read the 6.7 Cummins turbo guide. If a failed turbo or fuel pump has damaged the engine, compare engines by code on our engines page.
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