P0004
PowertrainFuel Volume Regulator Control Circuit High
Usually this comes down to corroded wiring or a dodgy connector at the fuel volume regulator, or the regulator solenoid itself packing up. The ECM watches the voltage on the regulator control circuit, and when it reads higher than it should the module flags P0004. The regulator's job is to meter how much fuel the high-pressure pump sends down the rail, so when its signal goes haywire the engine can't trust the fuelling. You'll see this far more on common rail diesels and direct-injection petrols than on older port-injection cars.
ⓘ Information only. This page provides general educational information about fault code P0004. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P0004 mean?
P0004 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Fuel Volume Regulator Control Circuit High.
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • Engine warning light on the dash, often the first thing you notice
- • Hard starting or a no-start, particularly after the car's been sitting overnight
- • Rough idle and hesitation when you put your foot down
- • Engine dropping into limp mode with the power noticeably strangled
- • Stalling at low speed or while idling at a junction
- • Fuel economy taking a hit on a tank you'd normally do better on
Possible causes
Causes commonly associated with P0004, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Damaged, shorted or corroded wiring in the regulator control circuit, the usual culprit on older cars where the loom runs near the engine heat
- 2. Loose or corroded connector at the regulator or the ECM, easy to overlook and easy to fix if you find it
- 3. Faulty fuel volume regulator solenoid that's failed electrically and is sending a high reading
- 4. A short feeding stray current from another circuit into the regulator wiring, which pulls the voltage up
- 5. Blown fuse or a tired relay in the fuel system circuit upsetting the supply
- 6. Charging system pushing too much voltage, a faulty alternator can skew the whole circuit's readings
- 7. Dead ECM or PCM, rare and only worth suspecting once everything else checks out clean
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Scan the car and note everything stored, not just P0004. Codes like P0001, P0002 and P0003 sit on the same circuit and tell you whether you're chasing a wiring problem or a control problem
- 2. Get under the bonnet and follow the regulator harness by hand, checking the connector for green corrosion, bent pins, and looking for chafed insulation where the loom touches metal
- 3. Check the fuses and relays for the fuel system before you go deeper, a blown fuse is a five-minute find and a cheap fix
- 4. Backprobe the control circuit with a multimeter and compare voltage and continuity against the workshop figures for that engine. This is where you separate a wiring fault from a duff solenoid
- 5. Measure the solenoid's resistance and its current draw, which usually sits around 35 to 80 mA when it's working. A reading way off that points at the regulator itself
- 6. Clear the code, take it for a drive and watch the live data to see whether the fault is solid or comes and goes, because intermittent faults are nearly always connectors or wiring
Common questions about P0004
What happens if I just keep driving with it on? +
You're risking getting stranded. P0004 can bring on stalling and no-start conditions without much warning, and if the fuelling goes badly rich or lean for long enough you can do real damage to the high-pressure pump, the injectors or the cat. None of those are cheap. Sort it before it leaves you on the hard shoulder.
How quickly do I need to deal with this? +
Treat it as soon as you can. It's not the kind of code you sit on for a month. If the car is still driving normally you've got a little breathing room to book it in, but if it's already dropping into limp mode or struggling to start, get it looked at this week rather than next. The cheap end of this fault is wiring, and wiring faults only get worse as the corrosion spreads.
Is it the regulator itself or just the wiring? +
Both are common, and that's exactly why you test before you buy parts. A high-voltage reading on this circuit is just as likely to be a corroded connector or a chafed wire as it is a failed solenoid. Plenty of people throw an expensive regulator at it and the code comes straight back because the real fault was a green plug. Test the circuit first, then condemn the part.
How long does the repair take? +
A wiring repair or cleaning up a connector might be an hour or two if the fault's easy to find. Replacing the regulator solenoid where it's a separate part is half a day. The painful one is where the regulator is integral to the high-pressure pump, common on diesels, because then you're pulling the pump and that's the better part of a day's labour plus the part cost.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →