This started after the recall last December to replace nox sensor and flash ecm. During regens the car bucks and runs rough, it will usually throw a CEL (2453 pressure sensor) I cleared the codes myself a few times and tolerated the rough running. In June I took it in for the CEL 2453 and they re-flashed the ECM. The next time it came on they changed the pressure sensor, but that did not help. I took it back and told them I was tired of this and to fix it. They gave me a courtesy vehicle (brand new Malibu) to drive. Three days later they said the plenum to the turbo was leaking so they replaced it. Today during the regen the car still is bucking and running rough, no CEL yet but I expect it will come on soon. I told them about the broken exhaust bolt that had caused a previous problem. They said they checked for leaks in the exhaust. The car has 74k miles on it so the warranty will not cover this. I am taking it back this Tuesday and they will throw more parts at it I am afraid how much this will cost. Any suggestions what to look for?