A Cat Burglar tried to cut off my cats in a church parking lot. They cut the y-pipe in 3 places, and one cut right through the front O2 sensor by the upstream cat. Mechanic ended up replacing the O2 sensor and rewelded the pipe but it only ran correctly for about 10 minutes. It began to idle extremely rough and slow. Mechanic said he reset the PCM after replacing the O2 sensor like you are supposed to, but there is definitely an issue. It was spitting codes out that said 2 cats were bad so they replaced them. They also went ahead and installed all new O2 sensors since insurance was covering all but the deductible. It ran fine for 5 minutes and then the rough idle started again. The codes then showed all bad spark plugs on 2,4,6,and 8 which is on the side the cutting took place. Replaced the spark plugs and it ran fine for 5 minutes. The codes then said one of the new O2 sensors was bad so he replaced it again. Ran good for 5 minutes then the issue happened again. No wiring issues seen, and the mechanic now thinks the computer was damaged during the attempted Cat burglary. Could the computer have been damaged when the saw cut through the front O2 sensor? Could some sort of electric charge back up through the computer and fry it? I’m at a loss and so is this very good mechanic.
I do not believe that the PCM could have been damaged during the theft of the catalytic converters, even if the O2 sensor harnesses were damaged, because that circuit would not be powered when the engine isn’t running. It is much more probable that there is damaged wiring (which the mechanic failed to see) or that the engine itself has been damaged.
Is this, by any chance, a Nissan? The reason I ask is because several Nissan engines have a design flaw which allows debris from a defective catalytic converter to be sucked back into the engine.
OP has a Chevy Silverado.
Did they disconnect the battery or connect one of these to the battery before welding on the vehicle?
If not, there’s no telling what happened to the electronics in the vehicle.
Tester
So the two mechanics that worked on my truck chased everything trying to figure out the issue. What solved the problem, so far, was removing the all new aftermarket O2 sensors and installing all new GM O2 sensors. It’s really weird, but all I know is that after 5 days I’m finally back in my 2016 Silverado Z71.
Did insurance cover the fees? Less deductible of course.
Yeah, but I’m still out $650!!
It seems that the replacement oxygen sensor had somewhat of a signal circuit short to voltage, this can occur with power from the heater circuit.
The higher-than-normal voltage signal will cause the PCM to lean that cylinder bank, causing the bank 2 misfires.
Catalytic converters should not be replaced while there is an engine performance problem, P0420 and P0430 faults would have likely gone away after the oxygen sensor repair.
I had this happen once. I replaced a lazy O2 sensor with the cheapest one at the parts store. It ran WORSE and got worse mileage than before. I spent more money on the one specified by the manufacturer and it was fine. If Bosch is OEM, replace with Bosch. If Denso is OEM, use Denso.
I bet a wonky sensor was just confusing the computer.
Good ideas above. If none of those, my guess is wiring to one or more of the o2 sensors damaged during cat-attack.