Is P0629 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.

P0629 Fuel Pump A Control Circuit High — Causes & Fix

What Does P0629 Mean?

P0629 is an electrical fault on the fuel pump's control or supply circuit. The engine may crank without starting, cut out, or run only until the primed rail pressure is used. Relay, fuse, wiring and pump-module tests come before replacing the pump itself.

P0629 at a Glance

What it means: The ECU has detected a fault on the fuel pump control circuit. The circuit reads high against specification.
Most common cause: Fuel pump / lift pump 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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P0629 Fuel Pump A Control Circuit High — Causes & Fix

What Does P0629 Mean?

P0629 at a Glance

Find the Exact Fuel Injectorby Vehicle Registration

Find the Exact Fuel Injector
by Vehicle Registration