What P0004 means
The fuel volume regulator (also called metering unit or suction control valve) is a solenoid valve on the inlet side of the high-pressure pump, used mainly on common-rail diesel engines.
How the engine computer detects it
The engine control module pulses it to set how much fuel the pump draws in and delivers to the rail, and in this way controls rail pressure. P0004 means the voltage on the control circuit stays too high for the commanded duty cycle, typically because of a short to battery voltage, or, with a switched ground side, an open circuit. The valve can then not be energized; a normally open design delivers maximum fuel and rail pressure rises.
Written from public technical sources and not yet checked by a mechanic. How we write these pages
Symptoms
- Check engine light on
- Loss of power or limp mode
- Rough running or diesel knock possible
- Excess rail pressure codes possible
Common causes
- Short to battery voltage in the harness Most likely
- Open coil or wire, reported as high with ground-side switching Possible
- Connector fault at the regulator Possible
- Output driver in the engine control module faulty Less likely
How to diagnose P0004
- 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.
- Inspect the parts involved: fuel volume regulator, high pressure fuel pump, fuel volume regulator wiring.
- Work through the causes above from most to least likely, cheapest checks first.
- 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
- 04
- Specific fault
Questions drivers ask
Can I drive with code P0004?
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 P0004?
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 P0004 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 P0004 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.