EngineLightCodes
Powertrain code

P0091 Fuel Pressure Regulator A Control Circuit Low

Severity
Fix soon
Typical repair cost
$90–$1,320
Do it yourself
Possible, medium
Shop time
0.5–2 hours

On common-rail diesel and gasoline direct-injection engines, a high-pressure pump feeds the fuel rail, a sensor measures rail pressure, and the engine control module regulates it towards a target from its maps.

How the engine computer detects it

The fuel pressure regulator A is the actuator the manufacturer designates for this: depending on the system a pressure control valve that releases fuel from the rail, or the control valve on the high-pressure pump. Some manufacturers report the pump valve under the "fuel volume regulator" codes instead. P0091 means the voltage in the control circuit is too low, typically a short to ground. Rail pressure can then no longer be controlled as intended, and the engine usually runs in reduced power.

Written from public technical sources and not yet checked by a mechanic. How we write these pages

Symptoms

  • Check engine light on
  • Reduced power mode
  • Hard starting or stalling

Common causes

  1. Control wire shorted to ground, or connector corroded Most likely
  2. Regulator coil faulty Most likely
  3. Fuse or supply voltage faulty Possible
  4. Output driver in the engine control module faulty Less likely

How to diagnose P0091

  1. Read every stored code with an OBD-II scanner. If misfire or fuel trim codes are there too, fix those first: they often cause this one.
  2. Inspect the parts involved: fuel pressure regulator, fuel pressure regulator wiring, engine control module.
  3. Work through the causes above from most to least likely, cheapest checks first.
  4. Clear the code and drive a full drive cycle to confirm the repair held.

Reading the code

P
Powertrain
0
Generic (SAE) code
0
Fuel and air metering, auxiliary emission controls
91
Specific fault

Questions drivers ask

Can I drive with code P0091?

Drive gently and only as far as you need to. The engine computer may limit power to protect the engine, so avoid highways and heavy traffic until it's fixed. If the check engine light starts flashing, pull over.

Will my car pass an emissions inspection with P0091?

Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.

Will P0091 clear by itself?

The light can go off after several drive cycles without the fault, but the code returns if the cause is still there. After a repair, the readiness monitors need a full drive cycle before an inspection.

Can I fix P0091 myself?

Often yes, with an OBD-II scanner and basic tools. Difficulty: medium. Start with the cheapest checks before replacing expensive parts.

This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.