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Gary, Buick Technician
Category: Buick
Satisfied Customers: 17019
Experience:  15 years master GM tech and mater ASE tech
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I'm looking on the rear o2 sensor on 2003 buick century

Customer Question

I'm looking for information on the rear o2 sensor on 2003 buick century
Submitted: 1 year ago.
Category: Buick
Expert:  Gary replied 1 year ago.

I am sorry your having this problem

this has a brand new GM converter or a direct fit aftermarket one and it still sets a 420 code ?

Customer: replied 1 year ago.
Expert:  Gary replied 1 year ago.

was it a direct fit or was it welded in place ?

Customer: replied 1 year ago.
I hate to say I honestly don't know. I got the car in 2011 and had the converter replaced and didn't ask too many questions...
Customer: replied 1 year ago.
basically I was now told due to the code to replace the converter but,
Customer: replied 1 year ago.
in finding out what I can the converter is not a "wear out" part and that code doesn't only mean that could be the problem
Expert:  Gary replied 1 year ago.

this code is set one of 2 ways

1 ) the cat converter is not up to original specs and is not converting correctly still setting the code

2 ) either the front or rear O2 sensor is reading wrong triggering the 420 code

what sets this code is when the front O2 sensor just about matches the rear O2 sensor as if they match reading or are very close the computer sees that and sets the code as a good working converter the rear O2 reading should be a lot lower than the front O2 sensor showing the converter is converting correctly

Customer: replied 1 year ago.
is it possible the rear o2 sensor could be throwing that code too?
Customer: replied 1 year ago.
right, awesome, that's what i've found... so
Expert:  Gary replied 1 year ago.

at this point replace the rear O2 sensor if it still sets the code the converter is not up to standards to clean the exhaust correctly

Customer: replied 1 year ago.
where is the rear o2 sensor located on 2003 buick century
Customer: replied 1 year ago.
if after replacing the sensor the code still comes up what would be the next step, would the converter then still have to be replaced
Expert:  Gary replied 1 year ago.

# ***** in this picture located under the car

the step would be to install a GM direct fit converter

Customer: replied 1 year ago.
how involved is it to change the sensor
Expert:  Gary replied 1 year ago.

very simple to do

pick up as new one and get under the car and it is very visual to change

Customer: replied 1 year ago.
what's the difference between direct fit and welded in place
Expert:  Gary replied 1 year ago.

the welded into place aftermarket cat converters where poor quality and 50 % of time will still set 420 codes as they do not meet the GM standards

Customer: replied 1 year ago.
I've read that converters typically are under warranty anywhere from 3-10 years, I'll of course call the shop I had the work done if needed, but is it typical for there to be any type of warranty
Expert:  Gary replied 1 year ago.

yes it should be under there warranty