Coolant Sensor Issues?

[xjoebradshawx]

This seems to be relatively common issue that I'm seeing in the forums, although I've yet to find a decent solution or guide, but maybe I'm just an idiot and looking in the wrong place.

My 2016 Fiesta ST (stock build.) 'overheated' today after about 5 minutes of driving. There were no physical signs of the car overheating, other than the engine temp sensor spiking, and the coolant and CEL light coming on. It's 40 degrees in New England today, so the engine was certainly not hot due to environmental issues. Regardless, after the car entered limp mode and all the lights came on, I pulled over, shut the car off and let it sit for about 30 minutes. I checked the engine bay and the coolant level was fine, and there were no visible signs of a coolant leak. I started the car up again and all the lights came on and the engine temp was spiked as well. I made the 5 minute drive back home, let the car sit for about an hour and restarted it and the same thing happened. I took it to the shop down the road and had them run the codes and it's throwing P1229. My immediate thought is a bad sensor, I'm just not sure which sensor to check first, or even where they might be located. Anything is helpful here!

 

[WannabeST]

Did you ever get this fixed? Given the situation I would've guessed your thermostat got stuck closed and no water was circulating. I had this issue on an old honda I had. It was in the 30s for weather and the car would overheat. With a stuck thermostat you basically have no coolant circulating, plus the water pump has more resistance on it so it's working harder.

 

[xjoebradshawx]

Did you ever get this fixed? Given the situation I would've guessed your thermostat got stuck closed and no water was circulating. I had this issue on an old honda I had. It was in the 30s for weather and the car would overheat. With a stuck thermostat you basically have no coolant circulating, plus the water pump has more resistance on it so it's working harder.

Still haven't found a fix for this unfortunately. The coolant temperature will spike immediately after the car is started, and will go into limp mode. I replaced the coolant temp sensor, and am still getting the same issue intermittently. It's gotta be something electrical, but I'm kind of at a loss of where to check now.

 

[scooter123]

I would suggest you purchase a vacuum filler or find a shop with one and have the pull a vacuum on your cooling system and use that to refill the cooling system. On big issue with these cars is that if you get a big air bubble in the radiator the reservoir can indicate normal level without giving you any clue about that giant air bubble. Note, if you want to know how large that air bubble can be run a tape measure from the floor to the fill point on the reservoir then draw a line at that distance from the floor on your radiator.

 

[Jabbit]

Still haven't found a fix for this unfortunately. The coolant temperature will spike immediately after the car is started, and will go into limp mode. I replaced the coolant temp sensor, and am still getting the same issue intermittently. It's gotta be something electrical, but I'm kind of at a loss of where to check now.

Did you reset the ECU? In my experience, limp mode stays until a reset takes place.

 

[WannabeST]

A temporary fix to your coolant spikes would be to just remove the thermostat. I wouldn't advise this long term but in the mean time it should keep temps pretty low.