Okay guys i have another problem to solve.

I pick up a new street bike for my birthday and i let my friend drive the x back to my house.(2001 e53 4.4i 135,000 mi)

Once we got home he got out of The car and yelled dude your transmission is fucked. That was the very last thing i wanted to here after spending a Ton of money.
So sure enough i drove it and its slipping and fail safe mode turns on. And the check engine soon lIght is on a light i have never had lite up before.

Ilitwide Not to worrie about it and enjoy my birthday.
So the next day i decide to jumb in and show my gf Whats going on. We drive it around the .neighborhood and everything is working fine! So im soo happy and everything is pefect again. We go home and then we want to go to Mall. I start up The motor and there check Engin soon light even turns itsself off. So we head to The mall witch is a 30 min drive about halfway the the.transmission start slipping and failsafe mode comes on..
I really wanted to blame it all on my friend but i dont think he did anything to it. I always drive it hard and it never has gave me any crap.

My thoughts are low fluid, bad trany thermostat thermostat, bad trany oil cooler. There is plenty of cooland.in.the overflow and the temp gage on the dash always stays right in the middle after its warmed up.

Also my battery is pretty old but i have a brand new alt. And its reading 13.7 volts at idle. I.charge up my battery all day while i.was at work and i drove it home today about 10 min drive and no slip. About to take it out for a long drive to see if it was the battery

Thanks for reading lets solve this problem.

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2001 x5 tan on black 4.4l 134,xxx