Second oxygen sensor

[Mato]

What does the second oxygen sensor do?

My downstream sensor is not connected, cable was to short.
Before I installed a JZW tune, this would result in a CEL code.
Now, after JZW tune no CEL code anymore.

Great! But, is it safe to run the car without out it, what does the second sensor provide or check for the ECU?

Possibly, you guys have a thread already, to cover this?

[WSW]

Pretty much tells the PCM whether the catalytic converter is working as it should.. No harm will be done without it, many people disable the second o2 when tuning

[Mato]

Ok, sounds good, thanks.
I guess when you completely unplug the second sensor,
It will not result in a CEL, I still have a cat and passed smog check, as well.

[comtrang]

I'm.not sure if its necessarily that it won' t throw a cel when disconnected but it can be turned off in the software which might not cause a code. Never tried it though.

[Mato]

Originally Posted by comtrang

I'm.not sure if its necessarily that it won' t throw a cel when disconnected but it can be turned off in the software which might not cause a code. Never tried it though.

I think John Williams turned it off in his ECU that is in the car now.

[PimpMyPc]

If you disable the rear o2 sensor, you may fail a smog test simply because the catalyst readiness flag is set to incomplete even though there is no CEL.

I've noticed that disabling the rear o2 sensor causes my EVAP system to get pissed and the tank vent valve will shut all the time when the car is running. Then the ECU calls for EVAP purge and collapses the gas tank until the car is turned off causing a weird "breathing" sound as air rushes in the tank vent and the gas tank expands again. Enabling the rear o2 eliminates this problem. YMMV

[Mato]

Luckily I just passed smog test, before I put the tune in, so I have some time on this one. If I get any troubles with the EVAC System, I plug it back in.
Thanks for the note!