Due to tolerances when manufacturing the injectors the injected fuel quantity may deviate between the actual and calculated fuel quantity. After manufacturing these deviations are established and an adjustment value is developed for each injector. With these adjustment values the engine control module corrects the calculated injection quantity and thus improves exhaust emissions. With this function the installed injectors adjustment values can be changed or stored again in the engine control unit.
The adjustment value consists of eight characters and is on top of the injector. Behind the adjustment value is also a double-digit injector identification, it is not relevant for the injector programming, it's only the first eight characters that is to be entered.
If an injector has been overhauled or replaced you have to check that the marked adjustment value on the injector matches the value stored for that cylinder in the engine control unit. If the engine control unit has been replaced an adjustment must be performed for all cylinders so that all installed injectors' adjustment values are stored in the new control unit.