Faulty fuel volume regulator (internal short or failed winding); Damaged, chafed or shorted wiring to the regulator, including a short to voltage; Corroded, loose or contaminated connector at the regulator or engine control unit; Fault with the high pressure fuel pump that the regulator is fitted to; Low or unstable supply voltage from a weak battery or charging fault; Fault inside the engine control unit driver circuit.

P0004

Fuel Volume Regulator A Control Circuit High.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
0: AreaFuel and air metering, auxiliary emission controls
04: FaultThe specific fault in that area

What it means

P0004 is the generic code for a high signal in the fuel volume regulator A control circuit. The regulator, which is usually fitted to the high pressure fuel pump, meters how much fuel enters the pump so that rail pressure matches demand. The engine control unit has detected a voltage or current in the control circuit that is higher than expected, which points to an electrical fault in the circuit or the regulator itself.

Symptoms

Engine warning light on
Reduced power or the car going into limp mode
Hard starting or long cranking
Rough idle or hesitation under load
Engine stalling or surging
Poor fuel economy

Possible causes

Faulty fuel volume regulator (internal short or failed winding)likely
Damaged, chafed or shorted wiring to the regulator, including a short to voltagelikely
Corroded, loose or contaminated connector at the regulator or engine control unitpossible
Fault with the high pressure fuel pump that the regulator is fitted topossible
Low or unstable supply voltage from a weak battery or charging faultpossible
Fault inside the engine control unit driver circuitrare

How to diagnose

Read all stored and pending codes and record the freeze frame data, noting engine load, rail pressure and battery voltage at the time of setting.
Check for other fuel pressure or rail pressure codes, as these help show whether the fault is electrical or mechanical.
Visually inspect the regulator wiring and connector for chafing, heat damage, water ingress, corrosion and bent or pushed-back pins.
Check battery condition and charging voltage, as low or erratic voltage can upset regulator control.
Compare actual and desired fuel rail pressure on live data while the engine runs, if the vehicle supports it.
With the connector unplugged and the ignition off, measure the regulator coil resistance and compare it with the manufacturer specification for that model and engine.
Check the control wire for short to voltage or short to earth and for continuity back to the engine control unit, following the wiring diagram for the vehicle.
If the wiring and regulator test correctly, check the high pressure pump condition and the control unit output as described in the manufacturer procedure.

How to fix

Replace the fuel volume regulator if its resistance or operation is out of specification.
Repair or replace damaged wiring and fix any short to voltage in the control circuit.
Clean or replace corroded or damaged connectors and terminals.
Replace the high pressure fuel pump if the regulator is integral to it or the pump is found faulty.
Repair the battery or charging system if voltage is found to be low or unstable.
Repair or replace the engine control unit only after all other causes have been ruled out.

Can I keep driving?

Medium severity

The car may run with reduced power or enter limp mode, so avoid long journeys and heavy loads and get it checked soon. A fuel metering fault can lead to stalling, which is a safety risk in traffic.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.