Welcome back! This video takes you along as I address a P0128 error in my 2018 Ram 2500HD with the 6.4L Hemi Gas engine. Essentially - the 6.4L in this generation of Ram has a Thermostat with a built in sensor and actuator to allow the computer to control it vs a purely mechanical setup.

When a part of this starts to fail (either mechanical or electronic) the system will catch a "rationality test failure" meaning the thermostat is not operating the way that the computer thinks it should be. This can result in problems with the engine coming up to temperature properly, etc. The thermostat and sensor is all one assembly that must be replaced as a unit.

MOPAR Part #: 4893177AD

Used for 2014-2023 Ram 2500, 3500, 4500 and 5500

I am not a mechanic - nor am I paid to make this video or endorse any specific part or method. PLEASE do your own research and use your own judgement before attempting anything shown in any of my videos. If you're not comfortable in your abilities, go to a mechanic :)