Who do you believe? ADAC or workshop?

Hello, maybe you have a tip for me. my Omega B 2.5 doesn’t start at once (starter spins and spraying also OK), then I called the ADAC and then he meant after reading the ECU that the speed sensor is defective, then the Omega was dragged to the workshop and that means now that the ECU is defective. Is there any way to get out what is really defective? I don’t have that much money for this or that a I would like to ask you to let me know which information may be needed to help me. Yes, I’ve already been looking for solutions here in the forum, but unfortunately I haven’t found the right one. nice Easter days