hello all, i am new to this scene. I recently found this site to be very very helpful. My engine light was on and i checked the codes via the tutorial left. I got code P0420 (catalyst low efficiency). I have taken my car to two mechanics and one muffler shop and neither can tell me what is wrong. I need to know exaclty where my O2 sensors are supposed to be located. currently I have one on my obx header, and on direclty in the middle of my catalytic converter, and am not sure if they were installed correctly. I have a 2003 Neon SE, any help as to where they are located on a stock Neon would be great, and/or any info as to what could be wrong. THANK YOU!

 

You should be able to see your O2 sensors by looking at your header and cat. It sounds like you can see both of them, i dont think that there is more than 2. Have you gotten a backpressure test?

 

i am able to see my 02 sensors but its just that i have been told many things as to where they should be. and no i have not gotten that test.

 

How many miles do you have on your car? Sounds like you have a bad catalyctic converter to me...either that or your downstream 02 sensor is bad.

 

my car has a lil over 60,000. however i just replaced the cat about two months ago. no word on where the sensors should be placed? i have one on the header and one directly in the cat, one mechanic said the second sensor should be behind, not in the cat.

 

The downstream 02 sensor shouldbelocated in the middle ofthe catalyctic converter...the code your throwing either means your cat is faulty or your sensor is bad IMO.

 

so in other words the set up i have right now is fine, it would either be the sensor or the cat, not the way it was installed?

 

It looks to me that your cat is bad or the sensor is bad...the downstream sensor could have been installed incorrectly or damaged during install but plugging in an 02 sensor is pretty basic stuff and it would be pretty hard to damage it or install it wrong.