whats the purpose of bypassing the o2 sensors?

[reef_chameleon]

I am getting ready to change out both of my o2 sensors. One of the only shops I trust around here in ( killeen, texas ) want to charge $200 for front and $200 for the back. I did the research in the forums and found out that it is not hard at all to change the rear o2 sensor. I just wanted to know what would bypassing the o2 sensors do.

 

[kenamond]

I am getting ready to change out both of my o2 sensors. One of the only shops I trust around here in ( killeen, texas ) want to charge $200 for front and $200 for the back. I did the research in the forums and found out that it is not hard at all to change the rear o2 sensor. I just wanted to know what would bypassing the o2 sensors do.

The rear O2 sensor just tells you that the cat is working. Bypassing it allows you to remove the cat without triggering an error code (check engine light).

The front O2 sensor costs $50 from oxygensensors.com (that's where I got mine) and is pretty easy to replace. You need an O2 sensor socket, but you can borrow one from Autozone or buy one for fairly cheap. It is a normal deep-well socket with a slot cut all the way up the side so that the O2 sensor wires coming out the tip of the sensor can stick out the side when you put the socket over the sensor. The hard parts may be that:

1) The O2 sensor is hard to get out. I use my normal 3/8" ratchet and a bicycle seat post over the ratchet as a breaker bar. Spray the sensor/O2 housing junction with PB blaster and let it sit for an hour before you try pullling it out. Some say that warming the motor up helps, too, but then you get to work under a car next to a hot exhaust.

2) Unplugging the O2 sensor plug can be a pain in the ass. The sensor wires are built into the sensor, and the other end of those wires has a connector that is attached to a bracket bolted to the passenger side of the head under the thermostat housing. The connector can't easily be seen, so you can't really tell how to unplug it by looking at it. Your O2 wires run over the exhaust mani heat shield, so you can trace it both ways from there. There is a 10mm bolt holding the bracket onto the head, and both the female and male connectors are attached to that little bracket. I just unbolted the bracket so I could pull it out and see what I was doing to unclip the plug. But it's one of those bolts that you get 1/12 of a turn at a time with a wrench, so it takes a minute or two to get the bolt off.

Use anti-seize on the threads when you put in the new sensor. You can get it in a ketchup packet type thing from any auto-parts store. It's like silver toothpaste. Makes future O2 sensor removal easier.

I've never replaced the rear O2 sensor, so I don't know much about it. If you're not getting an error code for it, I'd leave it in there. It doesn't affect how the car runs.

 

[DGajre777]

Awesome post Mack!

The rear o2 sensor is easier to replace than the front one. Just unbolt it from the exhaust pipe, take out the driver side seat and unplug the o2 sensor harness. I took mine out and replaced it with a huge bolt and run a o2 sensor simulator. No emissions testing here in FL, so I run a straight pipe without a cat.

As for replacing it, find another shop if you don't want to do it yourself. I won't pay more than $50 to replace both, it is a 10-15 minute job max.