Re: CEL - P0430 - Catalyst System Efficiency Below Threshold Bank 2
I would change the plugs, because this fault will do nothing wrong to new plugs. Worn plugs could in some cases set the P0430 code. The P0430 code is set, when the PCM sees that the downstream sensor reading is getting close to the upstream sensor reading. A good catalyser will burn most of the oxygen which remained in the gasses and the after cat O2 sensor should read an almost constant voltage due to the low oxygen contents. The upstream sensor should fluctuate a lot, because the PCM is adding and substracting fuel (trimming) to the base fuel schedule constantly, to get as close to the best air fuel ratio (14.7 to 1) as possible. When the catalyst looses its efficiency, less oxygen is burned of and the downstream sensor will more and more follow the upstream sensor readings, until at a certain limit the PCM will set the fault code.
An exhaust leak could draw fresh air into the exhaust, fooling the O2 sensor and giving a false message. So i would first look for any exhaust leak at bank 2.
Since you have a Diablo tuner, you probably can also see live data? I would scan the 1-1, 2-1, (upstream) and 1-2 and 2-2 (downstream) O2 sensors and see what the voltage readings do. A bad O2 sensor could trigger this code as well, so i would compare the bank 1 sensors with the bank 2 and see what the differences are.
There is a good change that the cat is getting bad, but better be sure then spending money for nothing.