To start with I understand that altering a vehicles emission system is illegal, I in no way, shape, or form encourage people to break the law. This test was done for informational purposes only. The vehicle has since been returned to stock form. On OBDII vehicles the purpose of the secondary (post cat) 02 sensor is to monitor oxygen levels in correlation with the primary (pre cat) 02 sensor to ensure that the cat is functioning. It does this by monitoring the oxygen level and making sure that there is a steady level of oxygen above a set percentage. So I had the idea that if the secondary 02 sensor was just hung in the engine bay it would see a constant level of oxygen and not set a CEL. The test vehicle was a 96 dx hatch with a stock Y7 and a manual tranny. I started with removing the secondary 02 sensor (leaving it plugged in) and using zip ties to secure it in the engine bay. I then removed an 02 sensor from a junk motor I had laying around to use as a plug for the 02 bung. It worked like a charm, I put over 1,000 miles on the vehicle and it never threw a CEL.