Is there any point replacing the second o2 sensor on non-californias?

[repo]

I don't have any codes it would be for preventative maintenance. The second one doesn't really do anything other than throw a code if the cat is bad right?

I've already replaced the first one as preventative maintenance. It was the original with 210k on it, haven't noticed any difference in mpg or anything with the new one.

 

[jgue467]

If I had No code I'd save my money for something else! :cowboy:

 

[mtbtim]

I wondered the same thing but i think the downstream can affect your gas mileage if the sensor becomes sluggish not reading the exhaust gases correctly. I recently replaced both the upstream and downstream 02 sensors on my 98.

Read this: Oxygen Sensors for Fuel Management Systems Are Key

 

[TheDurk]

I wondered the same thing but i think the downstream can affect your gas mileage if the sensor becomes sluggish not reading the exhaust gases correctly. I recently replaced both the upstream and downstream 02 sensors on my 98.

Read this: Oxygen Sensors for Fuel Management Systems Are Key

Tim, the article you cited is vague. But the only reference to rear sensors alone is this:

Catalytic Monitoring
In 1996, vehicles also began using oxygen sensors to monitor the operation of the catalytic converter. A “downstream” O2 sensor is placed either in or just behind the converter to monitor oxygen levels after the exhaust has reacted with the catalyst.
If the operating efficiency of the converter drops below a certain threshold that might cause an increase in emissions, it sets a diagnostic trouble code (DTC) for the converter and turns on the Check Engine Light.

All the rest is really talking about just the front sensor in terms of their function on the vehicle. The writer is just lazy as the means of operation of the two is the same and he also talks about that. The rear ones really do just set codes.

 

[mtbtim]

Tim, the article you cited is vague. But the only reference to rear sensors alone is this:



All the rest is really talking about just the front sensor in terms of their function on the vehicle. The writer is just lazy as the means of operation of the two is the same and he also talks about that. The rear ones really do just set codes.

I tend to agree that the downstream 02 sensor is just there for sensing the efficiency of the catalytic converter and has no influence on the air/fuel mixture and thus no effect on the gas mileage. But, I did some reading on different forums and some did say they thought the downstream sensor could affect your fuel efficiency.

Anyway, since I was replacing the upstream sensor, I figured it wouldn't be a bad idea to replace the downstream sensor at the same time since they were 20 years old.

 

[19963.4lsr5]

My 04 Grand Cherokee used the rear sensor to control target Air/Fuel ratio during warmup. After warmup it monitored The CAT.

Toyota.....don't know.


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[thecole1098]

I'm pretty sure mostly the MAF is used in conjuction with a preset fuel trim map during warmup (open loop) then the upstream o2 is used for closed loop operation.