2001 Buick Regal LS 6 Cyl 3.8L
PO420 error code. Please help!
My car runs good, but my gas mileage isn't the greatest. I get about 19 to 21 mpg in stop and go traffic. I also live in a very hilly area, so my mileage might not be that bad. I changed my catalytic converter about 5,000 miles ago because it was plugged. What else could cause a po420 code? O2 sensor, maybe? Wouldn't it throw a code for that? Any ideas of what I can check, or what it could be? Thanks in advance!
9 out of 10 times this means replace the catalytic converter. Since it is protocol to replace at least the forward oxygen sensor at that time, you could replace it now and clear the code P0420 and if it returns then you know for 100% that the cat is bad.