2012 Prius V, 179k miles, today I had the motor stammer/stutter after sitting with AC on for about 5 minutes. i It has never happened before, I shut it down for several minutes, checked the oil, coolant level, and looked for any disconnected thing but all was fine. So I restarted it without the AC just to eliminate that from the equation. It ran fine again, so I headed to Advance to check the code which showed the Coolant Temp Sensor. i didn’t want to buy their brand so decided I would get an oem one tomorrow. Before I reached home it did stutter again while driving almost like it was about to die. Managed to make it home. I do remember one thing about a week ago, I was rushing to the airport late at night to pick up a friend, I drove it harder than I usually do about 80 miles an hour for about 5 minutes. I saw a red light flicker on the dash so I immediately reduced my speed and it stayed gone, never returned. The next morning checked the coolant level and all was fine. But now I am thinking that maybe this is related. I did do a coolant flush back at 80k. The only non routine repair was doing the brake actuator replacement costing nearly $3k. i realize I am at that stage where things will begin to fail on a Toyota. It is due for a new set of plugs since I did them at 80k as well. After some reading here, I am thinking that possibly the water pump should be replaced. could these 2 things be the engine stutter culprit? there is no coolant loss and the oil look like honey, no milkshake. I will order from amazon an autel ap200 to help my diagnostics here, the ap2500e seems to jave worse reviews. Open to any suggestions on other code readers around $100 or less. Also where is the location of the Coolant Sensor? All youtube vids just show a standard gen 3. thanks in advance.
I think the P0177 code is a typo. The code for the engine coolant temperature circuit low input is P0117. When you get this code, it does NOT mean that the temperature sensor needs to be replaced. Based on your description, It appears that the engine overheated and caused the P0117 code. My guess is that the engine water pump is going bad. Preferred replacement is a Toyota OEM pump. The Autel AP200 is an excellent choice for a scanner for the Prius. It is capable of reading all the trouble codes in your car. Once you get the scanner, follow all the setup instructions. You will need to create an Autel account. After doing the setup of the scanner, run a complete diagnostic scan and see what you find. The next step is to use the scanner to run an active test of the engine water pump. This will run the pump at 3000 rpm, and you can see what the actual speed of the pump is versus the request speed of 3000 rpm. You may find that the actual speed is lower than the requested speed. You can also use the scanner to monitor the engine coolant temperature when you are driving. Normal temperature at highway speeds is 195F. When you use more throttle like going up a hill, the temperature could rise to 199 to 201F. If your temperature is going higher than 201F on the highway, I would replace the water pump.
^ This. For a little more explanation, the sensor is a "negative temperature coefficient" thermistor, meaning its resistance goes lower as the coolant gets hotter, and that's why a code whose fortune cookie reads "engine coolant temperature sensor low input" can be telling you the coolant was hot. To set the code, the reading has to be off-the-scale hot, so hot that the ECM thinks it could be an electrical problem and not a real reading. (Which it could be, say if the sensor wiring is damaged and shorting to ground.) But if it is a real reading, it's a very hot one.
