Chapter 2 in the repair saga for my 1996 Legacy Outback with 2.5l engine and auto transmission: Along with my transmission woes, I also have to contend with a Check Engine light -- P0420 (cat converter not up to spec). With nearly 200K miles on the original cats, I am not surprised. But in order to make this thing able to pass its next emissions test (coming up in October) I have to sink some serious $$ into replacement cats. Frugal as I am, I wonder would it really be necessary to replace both the front and back converters, or if relacing only one would do? If so, which one would likely provide the most improved emissions performance, front or back? Any thoughts or recommendations from you guys on this?? Thanks!

From what I understand the only way the computer detects a 'bad catalyic converter' is from the second O2 sensor after the cat. Maybe it's just the rear O2 sensor that's the culprit?

I thought that, too, so I swapped the old O2 sensor for a new one. No change.... (But thanks for the suggestion!)

I had the same problem when I changed the O2 sensor in my '99 GT wagon. It took driving for about 200 miles for the check engine light to reset itself.

 

Good luck,

murmur13

Well, unfortunately I've has the new one in for about 1200 miles, so I think I'm stuck with having to change out one or both cats. @#*&! Anyway, does anyone have a suggestion as to which one to try first, or a diagnostic method that will tell me which one is really bad??