Mini Cooper CVT problem - solved!

[Timm]

We bought a Mini Cooper with the famous CVT gearbox three years ago and it wasn't right from the start, but not having driven a Mini with a CVT we just thought it was the deficiencies of the system.

The car was bought with just 14,000 miles on the clock, even though it was an '03 model. The car was slow to pull away, the delay from standstill to selecting the correct gear was a second or so.

This continually got worse to a point where the car would pull away reasonably, but immediately the CVT would select a very low ratio (akin to 5th gear or so) and the acceleration was awful. Eventually we got the dreaded 'EP' and the car drove like a wheezy moped.

I cleared the error codes (different each time) using INPA, and that got it going again for a few days - but it very quickly reverted to awful performance and another Emergency Program warning.

We took it to BMW (Snows in Portsmouth) to get the gearbox oil changed as a first line of attack, and to have them diagnose what the problem was. They reported that the gearbox seemed fine after a 'gearbox reset' and the oil change. It took only a few miles before all the symptoms were back again.

Something on the INPA diagnostics report caught my eye though, and that was the battery voltage which was 14.9V, which is much too high, especially at tick-over. I know that the reported battery voltage is not that accurate, but that was certainly wrong - I decided to replace the battery.

And that cured all the problems! Although the car always started fine, the battery was failing. The car is now extremely lively, chooses the correct gears, pulls away quicker - in fact, it seems like a new car. The battery was changed over 5000 miles ago now and the CVT is working extremely well.

So, if you have CVT problems, try changing the gearbox oil and your battery before giving up.

[Sejanus]

Good to know. Nice detective work. Sadly though the problems you experienced aren't typical of the classic CVT failure.

[xviper]

What is the relationship between battery voltage and CVT function? Normal battery voltage under full charge is just over 14 volts. Resting voltage after sitting overnight should be around 12.5+ volts. So what you're saying is that your old battery was getting overcharged? What is it now? Isn't a too high a voltage an issue to do with the charging system?

BTW, my '05 CVT is still working very well (for those who have been following my posts on this topic).

[Timm]

The CVT is still operating faultlessly one year since my last post. My guess as to the reason the battery caused the failure would be the increased series resistance of it - a consequence of under charging and eventual Sulphation. A battery in that condition would not stabilize the alternator voltage effectively giving widely ranging output voltage, something that the Mini electronics was not happy with!

[omri617]

what is the correct amperage of 2002 Mini One (R50)? CVT?
thanks

[vcmini]

Timm,

I read your post and I was so surprised that my MINI was experiencing the same issues. I have a 2008 Mini Cooper Convertible.

Anyway, unfortunately I'm stationed in Bahrain so I had to take my Mini into a kinda Mini Cooper Dealer. They are more BMW but have a small small section of Mini Coopers. So basically they said "you need a new transmission, $4000BD ($10,638). I said no and took my car home. Fortunately, I knew that I had already needed a battery so after I saw your post I scheduled my car for a battery change. Now all good in the neighborhood. My car is back to normal.

THANKS for posting!!!!!!!!!!