2nd O2 sensor - do I need it?

[Rymanrph]

I realize that this won't apply to most since I have '97 wiring, but thought someone might know the answer. The '97 XJ had a 2nd O2 sensor past the cat. I don't have a bung for it on the MJ exhaust. There is a pig tail for it on the wiring, but my question is, do I need it? Obviously I didn't have one before, but I don't want to throw a check engine light if I don't use it. Can the truck run without the that sensor plugged in and not throw a CEL? My truck is hopefully going to the exhaust shop this week, so I can have i added if I need to.

[shelbyluvv]

With an OBD-II system it will throw a code for that sensor. It will cause the EGTs to get extremly high and melt your cat in a very short time.

[dasbulliwagen]

That second sensor is what is refered to as a catalyst monitor. the front sensor gives the PCM what it needs for fuel ratio, but the rear sensor makes sure the cat is doing its job, and it will set a code. All you need to do is buy a bung, drill a hole where needed after the cat and weld the bung in so you can mount the after cat sensor... no big deal really.

[terrawombat]

I've known many people that just hook up an O2 sensor to the wiring harness, zip tie it up onto the body somewhere and just have it read atmospheric conditions. It's not ideal, but it does seem to work for them and not set off a code. I personally went with an O2 simulator that is designed to withstand the dirty/muddy conditions under my Jeep.

[Rymanrph]

Since I have to have some exhaust work done anyway, I'll just pick a up a bung and have them install it at the same time. Easy enough. Thanks.

[1987Comanche]

Link explains the function of the secondary O2 sensor as well as the possibility of an O2 simulator. Since you're vehicle is pre-96 you'd probably be ok but check with the emissions gurus to be sure.

http://www.o2sensorsimulator.com/