Trouble Code P0730 Incorrect Gear Ratio:
This trouble code is not one that you should run into under normal circumstances. The main reason this code is going to pop up is because you just replaced your transmission with one that does not have the same gear ratio. A lot of people opt to purchase a used transmission of unknown or supposed origin but don’t investigate enough to find out that there are several gear ratio combinations. For the most part all 4T65E transmissions will interchange with one another physically but that is where it ends. The gear ratio MUST match what the pcm is programmed for or this code will set and when that happens the transmission will be in a max line pressure state which will cause very harsh shifts and TCC operation which is hard on the transmission. If you are replacing your current transmission with a rebuilt or used transmission and you are aware that the gear ratio is different than the original then the pcm/tcm must be reprogrammed properly prior to driving the car to prevent this code and its side effects from occurring.