I have seen a couple of posts about this issue, but none have solved my issue. I have a 2008 Unlimited Rubicon with 100k miles. I've run into an issue I can't find a solution to. I am getting a P2181 engine light and the ETC red lightning bolt light comes on during startup. In addition my thermostat gauge will rise and fall as I drive, if I'm driving down the road it'll be straight up as normal, but if I'm coasting or stopped, it'll be just above 1/4. The ETC used to go away by cycling the engine, but now that doesn't always work. I have replaced the thermostat and the Coolant Temperature sensor and the issue is still there. Using Fixd I was able to see that the coolant temperate reading is -40 degrees Fahrenheit. For comparison, the outside temp reading I was getting was 50 degrees Fahrenheit. This is obviously part of the problem, but I've replaced the sensor twice and it's a genuine Mopar sensor so I'm lost on where to go from here, any guidance would be much appreciated!

 

If you've replaced the sensor twice then that's likely not the issue. I'd look at coolant levels, make sure you don't have any air pockets, and then see about tracing that harness back to see if it's been chaffed somewhere to where you've got it grounding out. Unfortunately the loom they hagave us isn't a great quality so it does need replacement through the years to keep the wires protected.

 

Agree with the above.
I would definitely start with making sure you got all the air out when you replaced the sensor, and thermostat

 

I appreciate the response. I was going to check the voltage at the sensor, do you know what the voltage should be at the sensor on the harness side? Obviously not 0, but just some number to reference.