I had a code PO299 initially and had the turbocharger replaced. Then I was told the intake manifold and PCV valve needed replacing. I replaced the valve cover and PCV hose at the same time. I no sooner left the shop and code PO420 appeared. I went back and they told me I now have a bad catalytic converter. So frustrating. I tried cleaning the CAT with various chemical products...code remained. I've been driving the car with the CEL on for awhile now. It runs and idles great...better than ever. If I clear the code and drive at high speeds for hours on the freeway, the code will remain off. The code returns after driving a short time on city streets. What could be the problem other than the catalytic converter? I can't pass emissions test as is.
Okay look. Things are not coincidental. They worked on the car. You drive it out and that code comes on for inefficient catalytic converter. If they didn't do the correct throttle or the work that they did or even something as dumb as they put a PCV valve that is incorrect, it can change the flow of air in the vehicle, make the air fuel ratio imbalanced and then the catalytic converter will not run correctly and trip that code. Things just don't go bad while they're working on the car by themselves. That's a fact.
