I semi recently installed a magna flow catback exhaust. I am now getting P0420 and P0430 cat efficiency codes. I’m no expert but last I ever knew you wouldn’t have to tune for a catback due to it being past all the o2 sensors. Any explanations?

 

I don’t know specifics of magna flows, but if it’s creating enough back pressure, it could be affecting converter efficiency.

What do you mean by “semi recently”? It could be there’s another problem causing the codes and the magna flow is unrelated.

 

In response to the first part, Magnaflows are straight through mufflers, so I would think it would relieve the back pressure, but I’m not an expert so I could be wrong

When I say semi recently, it was a few thousand miles ago. The light came on almost immediately after install and my first thought was that there was more back pressure because magnas have a “break in” period where the I guess it would be called glasspacking is clogging it up and needs to be blown out. I ignored the light and cleared the codes. Bit, I’ve gone through that break in period, so if that’s the case it should have gone off after everything was blown out. I’ve gotten to where I just erase the codes when the light comes on. The only reason I don’t believe it is something else is that the codes are for both cats with sensors on them and of course the timing of when the light came on for the first time.

 

what year and engine?

 

It is a 2014 5.3

 

During the install, did you have to do anything that required dropping the front Y pipe with the converters? I understand you only changed the exhaust downstream of the sensors, but an exhaust leak upstream of the sensors can skew the readings.

 

The shop who did it says all they did was cut behind the 3rd cat(which doesn’t have any sensors) and install the magna flow system. As far as upstream from the 3rd cat nothing has been touched other than me doing a brief check on the o2 sensors to make sure they weren’t the problem.