I've just replaced a bad coil that I finally diagnosed after replacing spark plugs. It fixed the P0301 code but I have 2 remaining. The P0420 is the "Catalyst system efficiency below threshold (bank 1)" which I figured is going bad since I smell the familiar sulfur vapor. Any suggestions on fix? Also the P1320 is the "distributor signal interrupt" which I have no idea how to fix. I'm a die hard do it yourselfer and rather spend the time trying to fix things myself than be ripped off by the dealers. Any help is greatly appreciated.

 

I had that P1320 code on my dad's '99 GLE and it turned out to be coil related. The car had two bad coils that drove me crazy. What was strange about that was that I only got the coil code immediately after the SES light come on. If I turned off the car and didn't do the code scan, I wouldn't get the ignition coil code but I would get the P1320.

Can't help ya with the P0420 code...never experienced that one. Good luck.

 

i actually have had that code on for sooooooooooooo long haha
i have the franken car intake and i think i have the light cuz my intake is dirty...hopefully thats the reason, im trying to get the apex'i filter and that will hopefully fix the problem....i think the only fix is either removing aftermarket intake, if you have 1, or going to dealer and having them reprogram the codes so the cat is allowed more leniancy as far as exhaust fumes go
hollla

 

dealer fixed that p0420 code by downloading a update ECU program for free when I took it in when my service engine soon light came on.