Is P0004 always a pump fault?

No. Excessive injector back-leak is one of the most common causes of rail-pressure faults on high-mileage diesels — always run a leak-off comparison before replacing the pump.

Why does the fault appear mainly when hot?

Diesel thins as it warms, so marginal internal leaks in injectors and regulators flow more when hot. A warm-engine test catches faults a cold test misses.

Can a blocked filter trigger this code?

Yes. A starved low-pressure side stops the high-pressure pump building demand pressure. Check the filter and supply before high-cost parts.

P0004 Fuel Volume Regulator Control Circuit High — Causes & Fix

What Does P0004 Mean?

P0004 indicates the metering valve circuit is reading high — an open circuit, a short to battery voltage or excessive resistance from corrosion. The ECU loses authority over rail pressure and usually forces limp mode.

P0004 at a Glance

What it means: The fuel volume regulator control circuit reads above its expected voltage range.
Most common cause: Fuel volume regulator (IMV/SCV) failure
Severity: Moderate to serious — rail-pressure faults cause power loss and non-starts.
Can you drive?: Short distances in limp mode only. Diagnose promptly.
Typical repair cost: £40-£150 for sensor/regulator work; £100-£350 per injector where back-leak is the cause.

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P0004 Fuel Volume Regulator Control Circuit High — Causes & Fix

What Does P0004 Mean?

P0004 at a Glance

Find the Exact Fuel Injectorby Vehicle Registration

Find the Exact Fuel Injector
by Vehicle Registration