I’ve been having a Slow Down issue with my car lately. It seems to drive fine, however when I exceed 80mph or go past 3rd gear, for an amount of time, my engine starts to sound like a vacuum. Then next my car dash tells me to slow down. After that my engine shuts itself down where I have to pull off to the side of the road and wait like 15 minutes to start my vehicle and continue driving. What could the issue be? I took it to Autozone, tried a code reader but no codes were read, and worker said the car doesn’t have misfire codes or such.
This is quite common. The transmission is overheating.
The CVT oil is really supposed to be changed every 2 years or 30k miles. While I have seen people stretch this out to 60k without issue, I can’t recall ever seeing one cresting 100k without having changed it at least once.
If the fluid is not working effectively due to degradation, it will build too much heat which will trip the fluid temperature sensor and put the car into safe mode.
The flip side to this is the fluid has a monitor to determine more or less how useful it is, which needs to be reset when the fluid is changed. If the fluid was never changed, it is possible that the calculation based on the monitor is shutting it down out of safety when there is no pending issue.
Heavy whining is a warning sign. If it still operates OK when cold you may still be OK. I do strongly recommend having the fluid changed (with Mitsubishi CVT oil only!) and the degradation counter reset as it is long over due and you will experience a better operating transmission as well as a longer life from it as well if there are no current issues and this is a false alarm.
It is important to note that you MUST use Mitsubishi CVT fluid in this unit. As little as 4 ounces of incorrect fluid will cause permanent damage to the CVT, and that includes universal/Honda based CVT fluid etc. Mitsubishi’s CVT operation is different from other manufacturers and you must use their fluid.
There is a TSB on this issue as well. It requires replacing the CVT fluid dipstick to adjust for a different fluid amount to help prevent overheating.