I had my car out this past weekend and I was seeing a intermittent service engine soon light. It would periodically come on and off. When I pulled the codes with my scanner I had code 13 and code 44. I had the exhaust system replaced from the manifolds all the way back to of the car. The front y pipe has no pre cats and it ties into a magnaflow high flow cat in the middle of the car. Then out of that cat it goes to the rear y pipe then out via mid america motorworks quad power exhaust. I also replaced the O2 sensor when the exhaust system was done. Just wondering where to start looking. I disconnected the battery to clear the codes just to see if it was just a fluke but have not started the car since. Thanks for any insight that can be provided.