Bad Cat Converter Again

[black hornet]

I have a 2005 Si 5 speed hatchback with approx 138000 miles on it. last year I replaced the Cat and the downstream 02 sensor. It hasn't even been a year, and now I have a bad upstream 02 sensor and according to the shop a bad Cat Converter. My questions are, If I have a bad upstream sensor, will the cat throw a code also, & if I do not replace the 02 sensor or the cat will it cause any damage? I am thinking of just replacing the sensor to see if that works or will I just be wasting my money? So far the car seems to be running just fine, no decrease in mileage or performance. Any ideas would be helpful.

Thanks,

John

 

[RonJ]

Your engine is running too rich or misfiring.

Post ALL codes that are thrown. Do all these codes return after resetting the ECU?

When were the spark plugs last replaced?

 

[TokyoSkies]

Firstly, you should figure out why you're fowling O2 sensors. Usually, that's caused by running rich (way, way rich). May want to check your tune, and if you're relatively stock, reset the ECU (unplug the ECU while the car is off, leave it unplugged for about 20 minutes). Sometimes that helps. As far as replacing the Cat and O2, start with the obviously fowled part, first: the O2. If after those two things are complete, you're still having cat issues, take it to yet another shop, and get an opinion.

 

[TokyoSkies]

Your engine is running too rich or misfiring.

Post ALL codes that are thrown. Do all these codes return after resetting the ECU?

When were the spark plugs last replaced?

^ What RonJ said. Haha.

 

[black hornet]

RonJ,
The plugs are overdue for replacement by about 38000 miles and I have experienced occasional backfiring. do you think if I replaced them and the upstream sensor that that might resolve the problem before I replace the cat? What Are the best plugs to go with? I am thinking NGK Iridium. I will admit, I am mechanically challenged, Thanks for all your help!

 

[RonJ]

DEFINITELY START by replacing the spark plugs with the NGK ones listed in your owner's manual.

Don't replace anything else until you do this:

Post ALL CEL codes that are thrown. Do all these CEL codes return after resetting the ECU?