2009 Ford Explorer, 6 cyl, 4.0L, 74K. Read code w/scanner - “P0128 - Coolant Temp below thermostat regulating temperature”. Assuming this is pretty straight forward but was wondering what the most likely culprit is (?thermostat?). Ironically, this code popped about a week ago, I cleared it and actually got my inspection sticker earlier today and then later in the day, the CEL came on again and once again, the P0128 code. The coolant level is perfect so I know there aren’t any leaks.
Sounds like a thermostat is stuck open or randomly sticking open. Another possibility is a flaky coolant temp sensor.
Personally, I consider thermostats a maintenance item to be changed now and then rather than wait to see if it screws up; usually about 10 at night in the middle of nowhere.
Given the one in your vehicle is around 5 years old I’d change it out.
You’ve already ruled out a low coolant level, so that pretty much leaves the thermostat
While a faulty temperature sensor is a possibility, the thermostat is far more likely
You could spend time testing the accuracy of the sensor or the gauge
Or you could be quick about it, and just change the thermostat
Odds are you won’t see that P0128 for several more years, if you change the thermostat
Your thermostat is leaking, not externally but from the engine to the radiator. Due to emission requirements many thermostats have a rubber seal that can fail after 7 years.
+1 for ok4450.
Thanks for all the replies. I checked and the thermostat in this engine is pretty easy to change. Will be changing it in the next week - Thanks!