I have an INNOVA 31703 code reader and reading my prius as ive been batteling a check engine light. The issue with the engine light is P0420 code that causes the light. But when I go into the "enhanced menu" it shows "Current DTCs, Historical DTCs or Readiness DTCs ". I go toto "Readiness DTC's" and it shows P0303 and P0125. I have seen others in there when I first reset the ecm, but after the light is on I have seen these two in there before. Anyone have any experience with something like this before?
You probably need to replace the catalytic converter first, then address the other errors, if they still remain
P0303 is misfire on cylinder 3. Clear that code and swap ignition coils with cylinder 1. If you then get P0301 you need new ignition coil. P0125 is insufficient coolant temperature for closed loop fuel control. Very likely just thermostat. Pretty easy job to replace thermostat but it’s hard to bleed the engine cooling system of Prius.
The odd thing is, that under MIL lights on the scanner the only code is P0420. If I go to readiness codes, then the P0303 and 0125 are there. But they dont seem to trip an engine light?
