Q: 2008 Kia Sportage had extremely low or no oil or radiator fluid a day after ECM replacement and sensor lights did not come on.

ECM replacement does not implicate the engine lubrication or cooling systems. It is possible the fluid levels were already low when the vehicle was presented for service although admittedly it is also possible to envision a scenario where a shop employee "mistakenly" performed service on those components (i.e., worked on the wrong car) and, at the same time, forgot to add back the required fluids to your car. But, that is unlikely and you would have to try to judge the circumstances for yourself based on your first hand knowledge of the shop. If you do suspect leaks, at your request YourMechanic can perform a leak diagnostic. As far as the warning lights not illuminating, the oil pressure switch could be defective or you might have had more oil than you thought and so the oil pressure simply did not drop below the threshold designed into the switch. A vehicle can run normally if coolant is somewhat low. Consequently, there again, if you did not notice overheating you may have had "just enough" coolant so that an episode of overheating dd not occur. Based on what you are describing, there would have been no reason for the check engine light to illuminate. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.