Help!! Car will not shift past 40mph. Service Engine Light comes on and my codes are S038 & S073. Car drives fine as long as I keep it at 35 mph and below.

 

S038 = Electronic Level Control Exhaust(release) valve short to ground or open circuit
S073 = Right rear accelerometer fault
These codes are part of the Road Sensing Suspension, which raises/lowers the height of the car, as well as stiffens/softens the suspensions settings, according to the road speed.
Neither of these codes should effect how fast the car will go, or if/when the trans shifts. You might have other issues, such as an engine problem, or stopped up catalytic converter that is limiting the rpm/mph of the car. Does it shift thru all of the gears at lower speeds?

I say that it shouldn't effect the road speed, but it's possible that the PCM could limit the vehicle speed if the suspension was too high, or too low, for too long...it may be something that would be considered dangerous to drive by the engineers, so the PCM might be programed to limit the rpms. I don't know for sure, just throwing that out. I'd have to check the troubleshooting chart for more info...