I went to the dealer to have them reflash my pcm and the tcm due to a low idel problem listed in a service bulletin. A few days later I had the CEL with p0420 catalyst efficientcy. The car would not go above 50 mph.So I replaced the converter thinking it would fix the problem. But the car is still having the same problem and the transmission does not seem to be shifting properly. Does anyone know if the pcm can be reflashed improperly to cause such a problem.What else could cause the car to lose power and run sluggish.

 

Very unlickley usually a flash either will take (and the veh will run) or not(veh will not run). Sounds like either and o2 sensor issue or a over fueling problem.

 

The funny thing is that the car did not have this problem until the pcm was reflashed. The pcm and tcm both should have been reflahed. The guy from the dealer says both of them are done at the same time. I also changed the down stream o2 sensor when the converter was changed.