Prius Gen2 Misfire Diagnosis and Fix - Jan 16, 2025

Customer contacted me that their car was making a strange sound while driving. Test drove the car and no sound was apparent and no CEL or pending codes. I did jack up the front and tested the driver side of play. Everything was tight. I did find that the Inverter coolant pump was dead. Advised customer of the risk of driving without inverter cooling but they intend to get rid of the car very soon and it is the middle of winter. They only drive the car < 5 miles at a time.

Customer contacted me again several days later. Now the "engine sounds like it's going to fall out of the car".  I guessed "cylinder misfire" and went back to the customer's location with a couple of spare used ignition coils. Found a CEL and various misfire codes. Asked customer if they had been adding coolant (possible head gasket leak) and they said yes. Found "orange" coolant bottle and advised about proper Asian Pink coolant for the car.  Then started engine and the telltale Prius planetary gear rattle was there. Checked exhaust and no coolant dripping or smell.  No evidence of coolant leaking either. Fiddled with coil and injector wires with no change.  Cleared codes and ran engine again. Got a pending P0303, cylinder 3 misfire this time.  Replaced the cylinder 3 coil with a used one. Misfire resolved. $25 for used coil and $25 for the second onsite visit of 20 minutes. Customer pleased.