2013 Prius (240k) - P148F, P0301, P0302

Hi everyone, looking for some expert opinions on a 2013 Prius Two I just bought used two months ago. It has ~240,000 miles and what appears to be the original traction battery.

My daughter drove it for 1–2 weeks with the Check Engine Light on before telling me. I pulled the codes and I'm trying to identify what might be going on.

Confirmed Codes:

• P0300, P0301, P0302 (Random, Cylinder 1, and Cylinder 2 misfires)
• P148F (Engine Coolant Pump Over Revolution)

Current Clues & Symptoms:

• Starts and Runs just fine: No loud sounds when it starts However, my daughter said that there is a brief, "tick-tick-tick" noise at cold startup that disappears completely after about 1-2 seconds.
• Coolant Levels: The engine coolant reservoir on the far left is critically low (only about 2 inches of fluid left at the bottom). The inverter coolant reservoir on the right is full and normal. Fluid still looks normal and not dirty.
• Pressure Test: I ran the car from a cold start at idle for just a few minutes. When I cracked open the engine coolant reservoir cap, there was a loud hiss of heavily pressurized gas escaping.

I'm guessing that the pressure in the coolant reservoir is combustion gases and I plan to run a combustion gas dye test on it later today. If that's correct, my intuition is that the back pressure from exhaust gases is causing the water pump to cavitate/over-rev, and allowing fluid into adjacent cylinders 1 and 2 overnight causing the misfires.

Do you all agree? Anything else that might cause these symptoms. Is there any chance this is just a cracked EGR cooler? If it's internal engine failure should I try to rebuild/replace the engine or is it a loss at this point?

Thanks in advance for the advice.

 

Thanks Bryan 1954. I tested the combustion gas on the coolant reservoir last night and didn't get any color change. That was at idle with the engine cold (when it ran for a few minutes after a cold start). I may try again tonight. Does anyone know if there's anything on the Prius's that you need to do special for that test? I just saw that there is a way to get into a maintenance mode that let's the engine run constantly instead of letting the hybrid system manage it. I may try that.

I checked the oil and it looks clean. There are no drips/leaking fluids. I'm thinking about pulling the spark plugs tonight to check those and see if I see any signs of coolant. Anything else I could check? After working on it last night I noticed that the check engine light was off (maybe reset when I unplugged the MAF sensor) and we took it for a drive. It runs super smooth, so I'm beginning to doubt my diagnosis. I'm going to top off the coolant tonight with Toyota pink and then I'll watch to see if the check engine light comes back on after 20-30 miles or if the coolant level drops again.

Any more suggestions?