Flashing Cel Light Today

[crate]

Had a code thats comes and goes at times, which is P0430 Catalyst System Efficiency Below Threshold (Bank 2), i'm pretty sure my pass cat is going or is gone,

but going to work today my cel started flashing, so decided to head back home, put the scanner on it and had 2 codes one was the p0430...and the new code was p0306 misfire cyl 6. only flashes when i drive, if at idle stopped i doesn't flash only driving..

 

could this code be from the cat problem? or something else to look at check?

 

Truck runs great, idles great no signs of anything except the loss of some power which i expect is from the 430 code....

 

Truck is a 99 NBS 4.8l 183k

[95Sierra2500]

Well, you've got a misfire that needs to be checked out. First thing I'd do is check the plug to make sure it isn't fouled/crushed/broken, then run a compression/leak down test on the cylinder to make sure the valves are closing properly (just because it's easy to check and rules it out). Then you need to check to make sure the fuel injector is working (I believe this can only be done w/a Tech II or similar scanner). I don't recall if the 4.8 had a coil-on-plug setup or not, but if it does check the coil to make sure it's okay. Beyond that, I'd be at a loss on the misfire for one cylinder.

 

As for the catalyst code, get that cat replaced. It could be either plugged or blown out (they typically plug) and it can cause many problems, from bad fuel economy to excessive heat in the engine compartment, along with foul odors from your exhaust.