I am reaching out to the community in the hopes that someone else has had the same issues and found a solution. I recently purchased a '97 355 with a well documented service history. I drove the car home over 70 miles and all was good (no CEL). In July 2018 the cats were changed by the previous owner and the car passed smog. When I purchased the car it had to be tested again because more than 90 days passed. The car passed the sniffer but the ECU had codes so it FAILED. I took it to a local mechanic that works on Ferraris and he checked the codes which showed catalytic failure on both banks. Since the emissions were OK we decided to reset the codes and try to drive the cycle to clear the ECU. I drove about 30-40 miles and then the CEL came on. We installed extenders to the oxygen sensors and tried again but the CEL came on again. We changed the cats and the CEL came on again. Previously there were numerous pending codes but now just the catalytic is failing on both banks. No oxygen sensor codes now. We are unsure what to do next. The mechanic is a bit perplexed as both banks always seem to fail at the same time. Is there a bigger problem? Thank you in advance for taking the time to read this and I hope that someone else has had a similar issue and found a solution.