Final answer:
The correct procedure after replacing a defective EUI is to reprogram a new calibration code for that specific injector to ensure optimal engine performance.
Step-by-step explanation:
After replacing a defective Electronic Unit Injector (EUI) with a rebuilt/exchange unit, the correct procedure to follow is to reprogram a new calibration code for the solely replaced EUI.
The calibration code is unique to each injector and accounts for variances from the manufacturing process to ensure optimal engine performance. Therefore, it is not necessary to replace the engine's Electronic Control Module (ECM) or the personality module, nor to reprogram the calibration codes for all injectors unless they have been replaced or recalibrated.