Oxygen sensor

My '01 Buick Century,with 89,000 mi. needs 02 sensor replacement. What happens if it isn’t replaced immediately? poor gas mileage or serious consequence(s)?

It could lead to poor gas mileage. But the problem with that is, if too much unburned fuel reaches the catalytic converter, you end up not only replacing the O2 sensor, but also the catalytic converter. And you wouldn’t know the catalytic converter was being damaged because the Check Engine light is always on.


Don’t you want to fix whatever caused the oxygen sensors to go bad (IF they are, in fact, bad), first? If not, they will, likewise, go bad.
Who did the diagnosis, and on what proof was it based?

Poor gas mileage, poor engine performance, possible damage to the catalytic converter. It’s better to have the O2 sensor replaced than to gamble. Besides, as long as the check engine light is on you won’t know if some other problem develops.

Isn’t it true that there are two O2 sensors (on each side of the catalytic converter) and only the first one will impact performance and the converter?

My understanding was the 2nd O2 sensor is used only as part of the OBDII diagnostics to make sure the first O2 sensor and converter are working properly.

The OP doesn’t know which sensor is bad, but to answer the question, if it is the 2nd one, no damage will be done if it’s not replaced immediately.

Many thanks for all those who responded to my query. The consensus is that I should proceed with the costly replacement to avoid even more costly consequences.

Consensus? What consensus? Costly replacement? What costly replacement?
I haven’t even seen the diagnostic code; so, I’m not part of that consensus on that unknown costly part(s). If you would like to share specific data, that would help a whole bunch (to help YOU).

Buick technician quoted me “about one hour,$246”

It’s still not known to any of us if the car even needs an O2 sensor and which one it is.

I’m also not part of the consensus at the moment.

Was charged $45 for diagnosis(i.e.) DT DIAGNOSIS TIME: 426 CCT45.00 89455 FOUND CODE PO135 DECLINED REPAIRS 1.0 CHECK OUT The above is how it appeared on bill/statement.

If you had mentioned P0135 in your first post I think others wouldn’t have been so salty.


It’s a problem in the O2 sensor heater circuit. It could be the sensor or the wiring and connectors that lead to it. A good technician can test the sensor for heater resistance before he/she replaces it.