i have a 99se cali spec. Over the past year, ive replaced everything in the exhaust except the y pipe. This weekend it was the upper cat. three days later and my cel is on again. i stopped by my mechanic, he put on the obdII and it was the p0420 code again, which is why i brought it in last week. he didnt understand why, but suggested resetting the ECU, which he said would cost like $125. some guy would come and hook it up to a computer and reset all the settings. Does this sound right?

 

Not really, no. Never seen an option in CONSULT or any GST to 'reset all the settings' in an A32 ECU.

If you really want to 'reset' it, just yank the battery cable for a few hours.

Have you replaced the rear O2 sensor? That's the likely problem, or the wiring. Check the O2 sensor's readings with an OBD-II scanner or a CONSULT, and check the sensor itself. I really hope they tried O2 sensor and wiring diagnostics before going straight to the converter...

That or an exhaust leak. You say you have the original Y pipe, how's the flex section?