Re: Error Code P420 and timing chain replacement?
Kingsfr - As part of diagnosing the P0420, I looked at the output from the O2 sensor on the Bank 1 CAT using my Flukemeter (has a basic scope function). Clearly, the upstream sensor was performing less than ideal, so it would have been easy to conclude that the CAT was faulty. However, my approach was to rule out poor combustion first. Also, a new GM CAT costs a small fortune, so no need to jump to conclusions too early. Plugs were due for replacement, so it was a good place to start - didn't rectify the P0420, but it did run better. When the coil packs were replaced, the idle settled down considerably and the P0420 code vanished. Re-checked the output and waveform from the Bank 1 O2 sensor and it was perfect. I'm certain that a few CATs have likely been prematurely replaced due to shortcuts in troubleshooting. In my case, it was unneccessary. The scope offered irrefutable evidence that this was the 'right' fix.
'10 Acadia SLT1 AWD Med Brown Metallic 230,000+km