If CEL goes off, is the code cleared?

[lmacmil]

My check engine light came on and Autozone pulled P0133 (bank1, sensor1 O2 sensor) and P0420 (catalyst below threshold) codes. About a week later, while driving the CEL light went out and hasn't come on again. Question: are the codes still in the computer? Another question: is bank 1 the driver side or the passenger side on the 1996 OHV V6? Finally, the truck has 62,000 miles. Should I just replace both O2 sensors upstream of the converter under the assumption that if one is bad (or going bad) the other can't be far behind?

Thanks.

 

[Robert]

Which code came first? Typical repair procedures call for troubleshooting the first code that came up first. The problem here is that a bad catalytic converter can cause an O2 CEL and a bad O2 sensor can cause a converter CEL. If it were mine, here is what I would do. I would replace just the O2 sensor that failed since your catalytic converter is still covered under Ford's extended emissions warranty of 8 years, 80K miles. If you continue to get the P0420 with the O2 sensor replaced, let Ford look at a possible bad catalytic converter. If the fault doesn't come back, then just be ready to have to replace the other three. They typically fail anywhere from 60K miles to 100K miles.

Most automotive parts stores recommend replacing them at 100K miles regardless. I got my first O2 fault code at 95K miles so i went ahead and replaced all four. It's possible that you might be able to get another 30K miles out of the other two. Mine weren't hard to replace so yours are probably no worse. Even if another one fails in a year or two, it shouldn't leave you stranded. It just may run odd and your CEL will come on again.

Bank one is the engine side with cylinder # 1 which is the passenger side. I'm sure you've already figured out that sensor 1 is the upstream sensor (sensor before the converter).

 

[Robert]

Forgot to add, most codes will stay in the computer for 40 drive cycles. With the light off, either the 40 drive cycles have completed since the code last happened or the fault isn't present currently. If that is the case, the code should still be in memory.