I did some searching around but I couldn't find a satisfactory solution to my new problem. My '02 s80 t6 115xxx is storing a p0420 code. The reader says 'inefficient catalyst in bank 1' or something like that. Last month I was down two cylinders because of a failure in two ignition coils. Now I'm thinking that while I was down the cylinders I clogged the CAT or diminished the oxygen sensors somehow (I didn't think to take off the corresponding injectors to prevent fuel from going into the exhaust system). As I understand, there are two O2 sensors, one before and one after the CAT unit. Does 'bank one' mean the initial sensor is not reading? Can I take the sensor out and wipe it off? What about removing the CAT and cleaning it? Would I need to weld it back on? Thanks for your help in advance!

 

P0402 Exhaust Gas Recirculation Flow Excessive Detected
points towards the EGR valve. The EGR valve can get stick open due to a build up of carbon. You may notice a loss of power due to the over abundant amount of exhaust, which is displacing the air in the cylinder. This would cause the MIL to pop once it is hot. You might notice a strong gas smell from the exhaust due to the computer adding more fuel to counter the high cylinder temp and it will retard the timing. Therefore allowing more unburnt hydrocarbons to exit the exhaust.

 

Sorry...you said it was p0420. check out this site. http://www.obd-codes.com/p0420

 

I read the link you posted. The code is definitely p0420, not the other way, but I was confused at first too when I didn't write it down at the auto parts store.

The CEL has since turned off and I'm no longer getting the code. I drive quite a bit and I've been trying to get the engine to accelerate more smoothly at high throttle, so maybe while doing this I was able to blow some debris out the back end. Who knows, the car is so sensitive anyway.