Rear O2 sensor - bad if I don't replace?

[KrillBee]

I have a 1996 Nissan Maxima with a bad rear O2 sensor. I would prefer not to replace it but I want to know what the consequences are first.

 

[Bignate603]

You'll fail emissions if you have it in your state and over time it can do damage to your catalytic converter. You may notice a drop in your fuel efficiency also.

 

[fleabag]

I dunno, maybe not because the rear O2 sensor should just be there to make sure the catalytic converter is working and I don't think it influences A/F ratios like the front O2 sensor would.. That is usually why the O2 sensor in the rear is different from the ones in the front as the ones in the front are usually heated while the ones in the rear aren't cause their operation isn't THAT important....

 

[brblx]

Originally posted by: Bignate603
You'll fail emissions if you have it in your state and over time it can do damage to your catalytic converter. You may notice a drop in your fuel efficiency also.

no.

rear o2 is for emissions only, all it's doing is monitoring catalyst efficiency. it has no impact on mileage or engine performance.

 

[LTC8K6]

Yeah, the one right after the cat is often called the Catalyst Monitor.

 

[fleabag]

Though I DID read some anectdotes that some people removed the rear Sensor after the converter and found their car had low performance, bad mileage etc. etc. so I guess it really depends on the car..

 

[KrillBee]

Originally posted by: brblx

Originally posted by: Bignate603
You'll fail emissions if you have it in your state and over time it can do damage to your catalytic converter. You may notice a drop in your fuel efficiency also.

no.

rear o2 is for emissions only, all it's doing is monitoring catalyst efficiency. it has no impact on mileage or engine performance.

How does it monitor to it and what is the point of it? Does it cause a check engine light to come on if your catalytic converter is bad?

 

[exdeath]

Originally posted by: KrillBee

Originally posted by: brblx

Originally posted by: Bignate603
You'll fail emissions if you have it in your state and over time it can do damage to your catalytic converter. You may notice a drop in your fuel efficiency also.

no.

rear o2 is for emissions only, all it's doing is monitoring catalyst efficiency. it has no impact on mileage or engine performance.

How does it monitor to it and what is the point of it? Does it cause a check engine light to come on if your catalytic converter is bad?

The computer compares the reading from the rear with the one on the front, which tells it how much of an effect the catalyst in between had on the exhaust gas composition. If the delta isn't some predetermined amount, it raises a catalyst error code (light comes on). If I'm not mistaken, the rear sensor should always be leaner, due to the reduction reactions which increase O2, and the oxidation reactions which decrease hydrocarbons.

Anything that affects the delta between the front and rear sensors, anything from a missing cat to a bad sensor that is reporting incorrectly, will set the light.

Anything you do to get by the problem other than replacing the sensors, from disabling rear O2s in the computer or using MIL eliminators (terminators for the O2 harness that mimic an ideal O2 signal 100% of the time so as to remove cats or rear sensors without setting the light) is going to show up and fail an OBD2 emissions scan.