Hi all,

I have a 99 2.3 136k.

I have been gettting, off and on, a CEL and the source of this light is p0420 - catalyst system below threshold bank #1.

This CEL did not change after I replaced the cat with a magnaflow version.

Is it an oxygen sensor? If so is it the one directly on the cat or the other sensor.
Again the sensor is off an on. Currenly off....


Thanks for your help

 

Yup, bank 1 indicates which O2 sensor it is, it's the one ahead of your cat by the headers

 

imo i wouldnt bother with the sensor. there is usually a seperate code indicating a o2 sensor failure. I had the same code, same situation. the code reappeared after replacing the cat with an aftermarket one. pretty common problem, seems the car is extremely picky and if the cat is not oem then the dreaded p0420 will reappear.

 

I'm having the same problem&code with an aftermarket cat--the random tech one. I thought this was supposed to work as an OEM replacement and after maybe a year it's throwing this code. Should I suspect the O2 sensor or is it likely the cat?

If it's the latter, fuck that and I definitely don't recommend that cat. Not worth $275 if it's just going to fail.

 

Do you have a defouler? ^

 

No, I heard it wasn't needed with this cat. But I may go that route since I'm getting the code.

 

i would definitely try the defouler. imo theyre a necessity with aftermarket cats for this car. if youre not comfortable drilling out the defoulers you can buy a machined one on ebay for <10 dollars.just make sure to uplug the battery cables to reset the ecu

 

you need a defouler