RLM Posted May 4, 2019 Report Share Posted May 4, 2019 Okay I havent been in town for a couple of weeks and jumped in my 2013 C-Max SEL and got a couple miles from the house and had the coolant over temp light pop up with a check engine light. Turned back around and grabbed my code reader which I got P1299. So next I turned on the eternal test mode on so I can watch the digital read out of the coolant temp. Start up the car at 88C. At 121C temp light comes on. Turn back around to head back to the house. Temp keeps to clime. it makes its way yo 131C then jumps to 205C. It stays at the 205C till I park it. I turn the car off then right back on. Coolant temp now is readying 119C. I am figuring I need to replace the thermostat but just want to double check before I get into that. Quote Link to comment Share on other sites More sharing options...
plus 3 golfer Posted May 5, 2019 Report Share Posted May 5, 2019 The coolant temperature is an inferred value from the Cylinder Head Temperature Sensor. There is no coolant temperature sensor. Since it provide values from 88 C to 205 C it's likely OK. At normal operating range, CHT is about 7*F higher than the coolant temperature displayed based on my observations with ForScan. I assume coolant level is OK. After car has cooled down overnight. Do not start ICE. Check coolant temperature in ETM. If it's around ambient, then CHT sensor is likely OK. Make sure the coolant pump works. Start ICE and turn heater to MAX. ICE should run. Hot air should after a few minutes com out the cabin vents. Watch coolant temperature in ETM. Make sure grille shutters are open. Check if radiator coolant fan is operating. You may have to go for a drive to get coolant high enough for coolant fan or shut off heater. Changing thermostat and CHT sensor are not difficult and not very expensive. Thermostat is serviced from under car near oil filter but system needs to be drained. CHT sensor is on top of engine. Remove engine cover. See pic and note below. Cylinder Head Temperature (CHT) Sensor Note: If the CHT sensor is removed from the cylinder head for any reason it must be replaced with a new sensor. The CHT sensor is a thermistor device in which resistance changes with the temperature. The resistance of a thermistor decreases as temperature increases, and the resistance increases as the temperature decreases. The varying resistance affects the voltage drop across the sensor terminals and provides electrical signals to the PCM corresponding to temperature. Quote Link to comment Share on other sites More sharing options...
Keelowat Posted June 8, 2021 Report Share Posted June 8, 2021 what should I do if I find rust inside that cavity where the cht sensor is located? Quote Link to comment Share on other sites More sharing options...
jzchen Posted June 9, 2021 Report Share Posted June 9, 2021 I would guess it's time to do a coolant flush and fill with new coolant. Quote Link to comment Share on other sites More sharing options...
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