I have a 2012 EB and one of my he front O2 sensors has failed. I have two on the way and am going to replace the two front ones. I have some spacers to fix a CEL that I get while running the stock tune. Should I use the spacers on all four or just the front two?

 

You never want to run a spacer on a front or upstream O2 sensor, those are the ones responsible for correcting your fuel trims. If you're trying to get rid of a P0420 or P0430 code you would want to install spacers on the rear downstream O2 sensors, but this doesn't always work and you should verify that you don't have other issues such as an exhaust leak, misfire, overly rich condition, or clogging catalytic converters that would be the route cause of your P0420 or P0430 codes.

 

I am running high flow cats and with the stock tune it throws codes. I never run the stock tune though. But since I am replacing a couple of o2 sensors I got curious and didn’t want to cause more issues than fixing one. Thank you for the response.

 

yeah I run catless downpipes, and I have the 02 extenders the back 2 O2 sensors, and I have ran the stock program for the last 3 years, and have never gotten the engine light with the catless downpipes.