This code is for the 1/1 Catalytic Conv Eff. What is it for? And what could be the problem? I just change the spark plug and had a new exhuast put on (Flomaster muffler and magnaflow tips.)

 

well if you got your catalytic converter cut off its gonna throw a code and your check engine light will come on. there are things that will stop the check engine light from coming on but i don't know what its called

 

i didnt get it cut off it is still there

 

I have a Dakota V-6 magnum and have the same code pop up every now and then,i put some gumout fuel injector cleaner in and it goes away for a week or two so i researched a little and bought two new oxygen sensors($50 a piece front and rear) and the idle and fuel consumption got dramiticaly better and the check engine light came on again after about a month with the same p0420 code again.I am now wondering weather or not to buy a new Catylitic converter or not,but on another post i read that a couple guy's on here that have a flowmaster series 40(like i do)said that the light keeps coming on for them too cause of the change of the restrictive original muffler.So i will keep reading on here until i hear something different that i can try.

 

I have a 2003 ram 1500 with the 5.9 v-8 i also got a flowmaster muffler and magnaflow tips put on about 2 weeks ago and i just got the same code 2 days ago .

 

My first guess would be an exhaust leak. Did they weld the system or just use the cheesy clamps???

 

There are devices made called sensor simulators that can stop this code. They aren't exactly street legal because they essentially keep the O2 sensor from going out of range and causing the code. That doesn't stop people from using them, however.

I've been getting this same code on my old 4runner. The exhaust is completely stock and I don't smell unusual exhaust smells, can find no leaks, and the vehicle runs as good as ever. I just put a new downstream O2 sensor in it hoping maybe the sensor was just getting flaky. But, if that doesn't keep the code from coming back, I'm probably going to install a simulator on the O2 sensor until I start seeing signs of a real problem with the CATs (yes it has 2 CATs $$$$$).

The CAT system only has to lose 5% efficiency before that code will start popping up. That means it can still be 95% efficient and the sensors will still report it as being deficient. You can thank the great state of CA for all that BS.