Q: Car damaged by garage

I can comment on the need for the ecu, without knowing if they in fact damaged it or not. I can say that it is possible to damage any vehicle electronics when working on or near any power source such as the battery or alternator. If a positive (+) power source such as the positive battery cable, positive connection at the alternator, etc, are grounded in any manner, such as contacting them with a tool while another part of the tool is contacting the engine for example, that can cause a short-to-ground. Most vehicle electronic functions and sensor input or output, are controlled by the ecu controlling their ground (-). A short-to-ground can have that voltage spike run through any electronic component, including the ecu. If the ecu is damaged or shorted, the vehicle will run poorly or not at all. If that’s the case, the only solution is to replace the ecu to restore proper function to the vehicle.