(newer buicks) why is there a o2 sensor after the cat?

[tb3]

2 questions concerning newer cars (like my 3800 series 2)

1. why do they put a 02 sensor after the cat converter?

2. does deteriorating performance of the converter (over time and wear), affect the readings of that sensor to cause an effect on the performance of the engine?

thanks

 

[38turbo]

the second o2 gauge measures the performance of the cat.... part of an obd 2 engine management sys all cars after 2006 have this sensor after the cat.

 

[38turbo]

oh and it wont affect performance of engine but will cause check engine light and will cause failed smog test if you have them there

 

[tb3]

hmm. i'm at 125,000 miles and everything is running great.
so another words, don't be concerned about the cat until i get a check engine light?

thanks

 

[38turbo]

i wouldnt worry about it until theres a problem. as long as your engine is kept in good working order your cat should last for a long long time.

what ruins them is driving around with a poorly running engine dumping excessive amounts of unburned fuel into the cat

 

[tb3]

thanks for your help 38turbo. one last question. i've always put mobil one in this car since 5,000 miles, and change it every 5,000. sometimes, it may use up to almost a half a quart inbetween those oil changes (no leaks), so its burning it, which i know is normal. with the amount of miles on it now, you don't think theres any chance that oil consumption has gunked the converter up at all? bottom line is, i'm pretty preventive maint oriented, and want to keep this car running like new for a long time. i'm still averageing 28 mpg with this full size car. (lesabre)

 

[Pronto]

That second O2 readings are compared to the pre cat one and if there is too much variation it will throw a code saying the cat is no good. Remember the banned Caspers "O2 Simulator"? It went in place of the post cat O2 to trick it not to throw that code.

 

[tb3]

That second O2 readings are compared to the pre cat one and if there is too much variation it will throw a code saying the cat is no good. Remember the banned Caspers "O2 Simulator"? It went in place of the post cat O2 to trick it not to throw that code.

ah yes..., i do remember that fiasco. thanks pronto

 

[DailyDrifter]

the second o2 gauge measures the performance of the cat.... part of an obd 2 engine management sys all cars after 2006 have this sensor after the cat.

Your dead on. The first o2 sensor will have a very extreme waveform (cross counts) because its compensating for rich/lean conditions, the second o2 sensor reads after the cat has cleaned up and the waveform shouldnt fluctuate that much. Although sometimes you will have "lazy" o2 sensors that wont read a rich or lean condition and sends false info to the ECU.

 

[paintitblack]

thanks for your help 38turbo. one last question. i've always put mobil one in this car since 5,000 miles, and change it every 5,000. sometimes, it may use up to almost a half a quart inbetween those oil changes (no leaks), so its burning it, which i know is normal. with the amount of miles on it now, you don't think theres any chance that oil consumption has gunked the converter up at all? bottom line is, i'm pretty preventive maint oriented, and want to keep this car running like new for a long time. i'm still averageing 28 mpg with this full size car. (lesabre)

There is really only two things that will kill a converter. 1 is racing fuel, never put racing fuel in a car that has a cat, the lead in the fuel will clog the honeycomb inside. 2 is short trips in cold weather, when the engine is running and or warming up it creates a small amount of water plus in the exhaust you get some condisation. In cold weather without letting the motor completey warm up the water can collect in the cat and freeze, busting the internals. I can remember when i worked in a auto shop we would have cars up on the rack and u would be able to light your cigarette off of it. That kind of tells how hot they get and how u dont have to worry about it burning oil. Brian

 

[tb3]

good stuff to know guys. thanks a bunch!

 

[95' regal gs]

the second o2 gauge measures the performance of the cat.... part of an obd 2 engine management sys all cars after 2006 have this sensor after the cat.

All cars from 1996 on, not 2006. Some as early as 1994 had this also, pre-obd II obd II