After replacing a defective EUI with a rebuilt unit which of the following procedures must be performed?

• A. Replace the engine ECM
• B. Replace the personality module
• C. Reprogram the new calibration codes
• D. Nothing at all

Answer: (C)

When you install a rebuilt electronic unit injector, the system needs updated calibration data to match the new unit. Those calibration codes tell the engine control system the exact characteristics of the injector—timing, fuel quantity, and how it should operate for each cylinder. Without loading the correct calibration codes, the ECU would use mismatched data, which can cause rough starts, misfires, or improper fuel delivery. Replacing the engine control module or a separate personality module isn’t required unless those components are defective, and doing nothing leaves the system with inaccurate or missing calibration data. So the essential step is to reprogram the new calibration codes to ensure the injector and engine are synchronized.