Have you guys ever gotten a check engine light with code p0128. Drives ok, heater works. Tried turning car on and off and check engine light is still there. Mpg is down some to high 30s but it is a bit colder. Checked the coolant temperature sensor which looked ok. Thanks for you guys help.
I did a Google search and though not Prime specific there were several hits regarding coolant temp. Suggest checking coolant level and thermostat/sensor.
Any evidence of rodent damage to the wiring? The Prius wiring insulation is tasty to mice. If that's the problem you automobile's comprehensive insurance would pay for the repair. J
Thanks guys. I didn't see any damage to the wiring. I unplugged and replugged the temp sensor wiring. It didn't seem loose to start but double checked in this manner. I reset the check engine light and drove around for a bit. The light hasn't come back on but im the back of my mind I'm still wondering if its necessary to go in the the shop.
54 to 64 Celsius is stone cold. The attached screen capture is from a Hybrid Assistant report of a trip I took last Dec. Based on the starting coolant temperature, I guess I didn't start the program when the car was cold. Note the ambient (i.e. outdoor) temperature.
It's below normal operating temperature (80 to 90+ ℃), but if you had a stone at 54 to 64 ℃, you could toss it in your bed at night and be nice and toasty. (Wrap that stone in a blanket or something to make sure you don't wake up with a burn.) My Gen 3, if you are parked and just using the heater, will gradually drift its coolant temperature targets downward until it is cycling the engine to maintain around 50 to 60 ℃. That's warm enough to get nice toasty heat out of the vents. If you start driving (or turn off the heater), it reverts to its usual 80 to 90 ℃ targets.
@eveyo Hopefully you got one of those Bluetooth OBD2 units. Run torque app and watch the engine temperature for a couple of days. That's what I would do; if this was my issue. That temp sensor will effect fuel mixture. that's why your mpg is so low - your running rich.
Thanks guys. Yes I used the torque app and got those temperature values. I wasn't sure if the temperature was this way since the outside temp was in the 30 F to 45 F and if I was running some on electric. I have noticed my mpg be on the lower side in the 40s when driving normally locally and on the highway. I know this can fluctuate. Thus far I had thought perhaps the drop in mpg was due to the cold weather or my fairly new Michelin defender tires (about 1k in). I wasn't sure if the coolant temp was affecting it. The check engine light hasn't come back on yet so I am assuming all is ok.
Lower fuel economy is likely the new tires; EPA testing done with 3000 to 4000 miles worth of wear. Check their pressures. That'll drop with the cold, and effect fuel economy. When you checked the coolant temperature, was the cabin heater on? If off, the low temperature could be a sign that the thermostat is failing, and letting unhot coolant flow through the radiator when it shouldn't. Though if that is actually the case, I would think you'll see the code come back.
I've measured the same temperatures with both my heater on and off. Yesterday the coolant temp went up and measured 80 deg C and the check engine light hasn't come back on so hoping things are ok. If the light comes back on I'll take it into the dealer. I'm thinking the same with the mpg. Thanks
