2008 -C6 LS3 Z51 package 24K miles

I recently had an issues with 2 spark plug wires popping off for some strange reason. I drove the car about 25 miles limping home. Cleared the error messages and the car runs perfect. Although since that episode the engine light will not go out.

Currenty I have cleared the engine light twice after about 15 miles it returns on bright as ever (steady not blinking) The error code is PO420 catalytic converter. The readings at the tail pipe are in spec. I have only put on a few short trips since the spark plug issue.

I am thinking the catalytic converter has raw fuel and may need a "hot run" to blow it out. Any suggestions? I hate to put my baby to bed for the winter with the engine light issue. McDadee

 

Running with two cylinders not firing would have dumped a lot of raw gas down on the cats. It could have ruined them or it if both cylinders were on the same side.

 

The cat below spec light comes on when the cat drops below 95% efficiency(how many thing in life are 95% efficient). So there's not much room for lost efficiency before it pops the code.

 

2008 A6, with approx. 48k miles

Had a similar issue not too long ago. The culprit for the plug wire popping off ended up being a faulty ignition coil. I replaced it and it too care of the fuel dumping issue and running on 7 cylinders intermittently.

 

I have cleared the PO 420 Cat code several times. Once the car gets up to operating temp the light comes back. The car run perfect.....
McDadee...

 

I have cleared the code several times Once the car gest up to operating temp the engine light comes back. The car runs perfect. Any thoughts on how to clear the light so it stays off other than replacing the cat. converter. I assume that repair is big bucks$$$ The car only has 25K miles.

McDadee

 

I believe there is a recall on the Cats, so you could get them replaced for free. I think the recall is for for California cars or any other state that has stricter emissions requirements, New Jersey also comes to mind. It would be worth it to check.

 

thanks for the information. Ohio does not have emission testing requirements although I will diffidently check with GM to see if I can get some relief for replacement is that is the issue.

McDadee:

 

Something like the Scanmaster elm program with elm327 will data log the motor.

The key here is to check the O2's, since with the amount of fuel dumped, could have causes one of them to go lazy.

So during the data log, watch the pre and post O2 sensor output voltage readings to make sure that all 4 are ranging from 0 to 10V's.
Note, the 02's have heaters in them, and could be that one of the heaters in the O2 was burnt out. Hence if the car is fine when warmed up, but is throwing codes when the car is cold, could be a O2 heater was burnt out from being on too long as the raw fuel was being dumped on it.

If the all 4 are ranging up to 10 volts, now check the reading from the pre to post 02's. Hence the pre cat 02' voltage should be higher than the post 02's and if the differential readings not wide enough, this is causing the code. If it just one side, then swap the O'2 out between the left and right banks, and see if the problem is following the O2's or not. If the problem is still on the one side (did not follow the O2 sensors), then bank that you damaged a cat, and it will need to be replaced.

P.S, the first problem was driving the car in limp mode to begin with!!!!! When the vet has problems, either fix it there and then, or break out the AAA card to have it towed somewhere to fixed isntead. On this one you may luck out with a smaller repair bill if just a O2 sensor or cat, but when the car has oil pressure problems and you try to drive it still, it going to **** the motor, and that's a repair bill over $10K instead.

 

thanks dano 523. I will have my shop run the test you suggested. when we clear the code with the engine cold it takes about 15 min or operating temp for the light to re-appear then it stays on cold or hot. I am having a tough time wrapping my mind around a cat replacement that will be north of $1,000 $$ for (1) ea. I have had similar problems with my ford truck blowing a coil on a spark plug and driving some distance firing on 7 cylinders until I could get home to replace the coil. Never had a problem with a cat code..... /engine light. Following some of the issues others are reporting with their cars, I hope this is not the start of a C-6 money pit..... McDadee