P0422 Error Code

Just got back from Advance Auto Parts... a free diagnostic check for the cause of the engine malfunction light turned up error code: P0422. After some research online it's suggested the problem is either the
CCV- canister control valve, an oxygen sensor, or catalytic converter issue.
My questions are: 1. I just had my coil pack replaced, along with spark plugs and an injector service. Could this have caused the problem?
2. Should I take it back the the place that replaced the coil pack, replace the sensor myself to see if that was it, or go to the dealer?
Thanks. Oh, and what is this going to set me back?
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P0422 indicates your catalyst efficiency is low. If you had a misfire issue, I'd primarily suspect that the converter was damaged by driving the vehicle while it was misfiring.
The converter in question is the one between the front and rear oxygen sensors.
If your car drove normally after repairs, this problem wouldn't have been detectable by the rapair facility until the check engine lamp eventually came on with the diagnostic trouble code. For that reason, it's doubtful you'll receive any assistance with repairs.
If you're within the 8 year/80,000 mile warranty on the converter, you might try taking the car to the dealer. Of course, if they see new aftermarket wires, they'll probably figure out what happened.
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Took the car to the dealer. Dealer said it was a bad catalytic converter and they replaced it no charge because it was under the 80k miles. Now that I've driven the car 100 miles, the check engine light is back on. I'll be bringing the car back to the dealer for the next step. Still not sure what I'll do about the 1st shop that repaired the coil pack, if anything. I guess if the dealer discovers that to be the problem, I'll have to take it back to the 1st shop. I'll keep everyone posted.
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Dealer reports both the catalytic converter and pre-cat were bad. All covered under 8/80 warranty.
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