Purpose: Sometimes people choose to hollow out the catalytic converter on their cars. If you do this, the second O2 sensor sets off an error code and then sets off the famous SES light. This light is saying that you need a new CAT. Here is a cheaper version to the ones I have seen on the internet. Don't be another fool getting ripped off.
Note: Credit for this mod must go to Rodney Chalker.
How it is done: First thing you need to do is go to Radio Shack or just your local electronics store for a pack of 100k resistors. You will need only one. Find the O2 sensor on the U-Bend or wherever you may have placed it. Unplug the harness from the O2, bend the tabs up on the heat shield holding the harness, now pull enough of the harness down to get the four wires out of the conduit. The wires you need to splice into are BLACK with no stripe and PURPLE with white stripe. Now just connect one end of the 100k resistor to the BLACK wire and the other end to the PURPLE/white stripe. Tape it up good and put it like it was before you destroyed the insulation. Don't forget to plug the connector from the O2 back into the harness.
This mod only works if you have your O2 sensor in the exhaust!!
The direction of the resistor is not important.