I have a 2013 TC that stumbled and threw code P0978 - Shift Solenoid. The fluid was replaced in the last 5,000mi, and it hasn't been otherwise problematic. After letting the car sit for a bit, it just...went away. Another few hundred miles with no issues.
From reading, it seems like this could be something with electrical wires, or more likely, something internal to the transmission? Is there a good way to go about diagnosing whether this is internal or not? Can the solenoid unit be replaced without pulling/replacing the whole transmission?
If it needed to be replaced, is there an upgraded unit available? I've read that TCs see transmission issues fairly regularly, and I'd rather solve the problem by spending a bit more now, then to see it come back in a few years. This van has well under 100k miles.
This van is commonly used to carry about 800 lb of stuff long distances, and it would be a bigger deal than usual to get stranded, so I'd like to prevent any issues going forward if I can.
