I bought a used lown Milage engine from japan install it myself and at start up it started normally then about in 10 minutes got the check hybrid engine and all lights on dash turn on then the car turn off and did not start I reset hybrid battery by disconnecting orange plug then negative post from 12v battery and white connection at fuse box for 10 minutes on fuse box. Then started it again and engine lights on dash came back on and car turn off the check hybrid battery came back on. I used my exhaust from original engine but left intake with throttle body that came with engine also left fuel injectors from japan engine and all sensors. Read threads about fuel pressure, throttle body, and some connections not connected correctly. I decided to replace intake with my original motor and throttle body removed all sensors from my engine and replaced all to japan engine along with fuel injectors I connected everything back on and this time put motor in diagnostic mode (this setting will start motor with gas engine and not with hybrid battery mode to get engine up to temperature and bleed coolant and check fuel pressure) engine started normally check coolant then turned engine off. Went to start prius then no check hybrid battery after that, couldn't tell you if throttle body, injectors,or sensors where the problem I guess I got lucky and light turned off. Car is driving normally with no issues.
It was probably one of the sensors. Different setting in japan then in America. And "diagnostic mode (this setting will start motor with gas engine and not with hybrid battery mode" is not really true. The hybrid battery turns the engine over to start it. There isn't a conventional starter on the Prius.
