Check engine light has been turning on for a few days then it'll turn off for a few days. I took it to get read and the code was p0420. I have replaced all spark plugs and coil packs. Is my cat shot? Why woukd the CEL be turning off and on? This is on a 07 expy. It was misfiring a few months ago that's when I replaced sparks and coil packs.

 

No need to replace the coils and plugs again. It could be a number of thinks. Leaking injector, bad cat, etc. I suggest you take it to a shop you trust. Throwing parts at these things are often costly and fail to solve the issue.

 

Is it safe to drive 600 miles in it? I need to make a trip this weekend. The truck runs great. Its just the light keeps turning off and on

 

I can't say. Unplug the battery for 15 minutes and see if the code stays out. If it drives fine, doesn't buck or idle poor, fluids are ok, it should be fine.

 

So a quick run down, is your O2 sensor voltage changing quickly or slowly? ECT in the proper range? What is the mileage on this rig? You said a few months ago you replaced plugs and COPs, how long did you run with a down cylinder, is itpossible enough fuel was dumped to damage the the O2? Was the failed COP/Plug on the same side? Remember as no one has pointed out this is a bank one failure so it's just 1/2 of the engine having issues. I would drive it personally if it idles and seems to run fine you just may burn more fuel than you want to.

 

You could try to swap the downstream o2's side to side, if the code changes to bank 2, then you know your o2 sensor is shot.

 

Montecarlo, I have 101k on the odometer. We ran it maybe 50 miles with a down cylinder. How do I check O2 censor voltage? And the ECT range?

 

If you want to get dirty, go underneath the vehicle and back probe the wires with a multi-meter. While your under there smack your converters and see if they sound like theres a million broken pieces in there, bad news if it is. Or stay clean and plug in a reasonable scan tool to your obd2 port.

 

I need to buy a multimeter but I did get under the truck and smacked the converters. it doesn't sound like anything is loose in there