Injektor ohne Eingabe seines Kalibrierwerts eingebaut

An injector was replaced and its calibration code never programmed into the module, so the module continues applying the previous injector's correction — or none.

This is the commonest reason a diesel runs badly immediately after injector work, and the reason it costs money is that it looks exactly like a faulty new part. Uneven idle, a harder knocking note from the affected cylinder, smoke and poor economy are precisely what a worn injector produces, so the natural conclusion is that the replacement is defective. Fitting a second one changes nothing, because it will not be coded either.

Nothing is broken. A step in the job was not done. Coding takes a scan tool and a few minutes, and nothing about fitting the injector accomplishes it automatically.

A related trap catches reconditioned injectors specifically: a remanufactured injector is flow-tested again after rebuild and issued a new code, supplied on the reconditioner's paperwork. The code stamped on its body is the original one and is no longer correct — entering it produces the same fault as entering nothing.

Beyond the running quality, there is a reason not to live with it. An uncorrected injector may be over-delivering, putting more fuel into one cylinder than the module believes on every mile driven, at higher local temperature and pressure. That is a slow risk to the piston rather than an immediate one, but it is real.