I have exactly the same fault on my daughters Fiesta 2005 1250cc petrol: Speedo not working; ABS light, malfunction light and handbreak light constantly on. Fault code U0121 ABS Comms failure. I purchased a new ABS ECU from Ford (£400+) and wanted my local mechanic to fit it.

However, the instructions in the new ECU said you need to read the ECU code from the faulty unit and then afterwards program it into the new ECU.

My mechanic has now refused to do this job as he said he does not have the tool to read and write the ECU code. As the new ECU box has been opened Ford will not take back.

From this thread, it would seem that the Fiesta does not require writing of the coding to the ECU. I would really appreciate it if this could be confirmed by someone?