Jut install a TBE with a test pipe insted of HFC. But now after driving it for a few hours, there's a SES light.. I pluged my OBD2 scanner and it gave me a code of PO420. Is this because I need a tune? Or its just the test pipe thats causing the SES light to trip? Any help would be great.... Thanks.

 

When you searched for that code, you didn't see the hundreds of times this has been explained? It's the rear o2 code that always happens...

 

A test pipe would generally result in a rear o2 sensor code as the engine is thinking the cat or the sensor itself has failed. There are hacks to avoid this though (don't recall the keywords to search).

 

Search of 'CEL fix'... You'll find a quick fix for it.

 

Search for "Anti Fouler" and you'll find tons of "fixes". I used one anti fouler on my HFC and it worked perfectly....no more SES light. Only cost me 2 bucks for 2 of them. Any autozone, pepboys.......will have them. Don't forget to use plenty of Anti-seize too!

 

P0420 dtc is Catalytic Efficiency Below threshold Bank 1,it is not that your rear o2 sensor is bad(that would generally be a p0136).It means that your HFC is not working as well as the stock cat converter and the ecu is telling you this.As recommended above get some kind of "fix" for it,searching would yeild many results.