Recently took my 2010 LT to the local muffler shop after my exhaust started getting loud and leaking fumes. They basically replaced the whole front half of the exhaust system, and now my car is throwing a p0420 code. It had the light on prior to the fix, but it was an emission leak code. When I took it back to the shop they told me I had to drive it for a while to get the code to go off. Is this true? I'm fairly certain they used an aftermarket converter. Could that be my issue?