ТНВД заменён без калибровки

A high pressure pump fitted without its calibration being written to the module. Modern pumps are individually measured and carry correction data, exactly like injectors — and a module running the old pump's corrections against a new pump is working from a description of a part that is no longer there.

The engine runs, which is what makes this deceptive. The errors are small enough to start and drive on, so the complaint is rough running, poor economy, or a fuelling code rather than an obvious failure — and every mechanical check on a brand new pump passes.

The remedy is to enter the pump's own data and run the relearn, which is a scan tool operation rather than a mechanical one. Read back what the module holds and compare it against what is printed on the pump — a mismatch is the whole diagnosis. Adaptations from the old pump should be reset too, since corrections learned against a worn pump are wrong for a new one.