I have a 2007 GMC Yukon that has the code p0420 and p0430. I looked on my scanner and the code seems to trip at idle. I had a mechanic say it was a vacuum leak and he fixed it but the light came back on a day later same codes. I took it back and he says it was the catalytic converter. I replaced the catalytic converter, O2 senors and the spark plugs and air filter. Check engine light stayed off for 3 days until it comes back on with the same codes. I checked the freeze frame and the code still trips at idle. The idle looks relatively low sitting at about 553 RPM and the battery voltage seems to be up and down. It seems to charge at 14 but after a while of driving it seems to be around 12 volts. I’m not sure if these can be related but i really need help because i’m almost ready to burn this truck to the ground or let it roll off a cliff. Thank you Scotty!
I would load test the battery and alternator and take care of them (if needed) to rule out the electronic issue due to the low voltage,. Did you use OEM sensors? Have you checked for leaks in the exhaust?
