I just got a 2001 Prius and it runs good, however once left overnight it dies in few seconds after started. Then I get the check engine light, and 3 icons on the LCD screen - PS, Main Battery, Car with Question Mark. There is only one OBD code - 3191. I read a lot on the Internet and decided it has to be the ECM. I ordered a used ECM from eBay and I have the following question: I can replace the ECM myself, but do I need to bring the car to the dealership to have the new ECM flashed, or is it going to run just fine once I replace it?
It could also be the throttle body or the fuel pump relay, keep that in mind... a point-diagnosis before starting to swap parts might be prudent. . _H*
You might check the throttle body to see if it or the gears are sticky: Cleaning Prius Throttle Bob Wilson
DTC P3191 can be caused by engine oil viscosity greater than 5W-30 or overfilled engine oil level. It can also be caused by inadequate fuel line pressure, as well as tune-up issues like worn spark plugs or a dirty throttle body and throttle plate. Given that you have already committed to buying a replacement ECM, I hope that you bought the correct part number: 89661-47054. A prior version ECM will not help to address this problem. The reason that it is necessary to replace the ECM is because it is not possible to reflash the operating system within. Hence, all that you have to do is to install the correct version ECM.
