"which is a bit worrying for me as it suggests that instead of the pre-cat, it could be other things that cause P0420/0430"
Yes, which is why the Berrymans B12 is a good first step to try to fix the problem. I tried Berrymans for a few months before I gave up and went to the mileliminators.
" and would it be better off to have the mechanic to check those first"
Unfortunately, it might cost a pretty penny and not take care of the problem. Most times, a mechanic will just change an O2 sensor when they see a(ny) CEL code. The only way to really determine if it is a precat issue is to get a real time scan of the PCM and see what the rest of the engine was doing when the code showed up or was doing before the code showed up. And then analyze the parameters. In your case, your mechanic determined it was the Bank 1 Precat. The dealer made a big mistake in his diagnosis.
"(as failing emission is one thing, letting the engine deteriate and may be stalled in the middle of the road is much worse) ?"
Once again, if it is one of the other reasons for the P0420 code, the Berrymans B12 might take care of some of it. Note that some of the other reasons could also trigger other codes which will then help narrow down the problem.
"Also, out of my curiosity, if this DTC code is calculated based on the pre and post O2 sensor readings, and that the downstream O2 sensor is after the main cat, how can it know it is the pre-cat(even pinpoint which one) that is the problem ?"
OBDII 1996 V6 Duratec and newer.
Upper O2 sensor is before the Precat. Lower O2 sensor is after the precat and before (not after) the main cat.
Bank 1 has one Upper and one Lower O2 sensor.
Bank 2 has one Upper and one Lower O2 sensor.
This is how the PCM determines whether it is Bank 1 or Bank 2.
The PCM will not be able to determine if the main cat is "shot". That will probably be determined when you go for a tailpipe emissions test and it fails.
Edit. If it is a precat issue, the "Rolls Royce" fix is, of course, to change both precats, the main cat and both Upper 02 sensors (it is probably due for new Upper O2 sensors anyway at 100k miles, easier to change it when the precats are not in the car). For that, you are looking at $2700 or so.
Last edited by Tony2005; 06/06/06 08:59 PM.
