Well here is the update, it was the voltage regulator. Two weeks and approx 70+ miles and no more errors

My conclusion is that once I noticed the coolant leak (reservoir split) and decided to just keep putting in more coolant hoping the problem would go away was a very bad decision. Coolant draining down onto the Voltage Reg. caused the failure. So if your reservoir is leaking go ahead and change it fast and avoid this problem.

I may have the same problem
 

:dunno:

SlickGT1,

I sent this in a private message but thought I should post to the thread instead.

I saw your post on flipping the transfer case actuator gear and wondered if the issue I'm having might be solved by doing the same. I have a 2002 X5 E53. I engaged the cruise control while driving on a level road. As I started to climb a slight, gradual grade the X5 started to accelerate to climb the small hill. Almost instantly the X5 seemed to stall and surge violently. The car would not accelerate and multiple lights came on as the instrument panel displayed a DSC failure, Trans failsafe prog, and engine failsafe prog. Is this the same sort of thing that happened to you. Any help you could provide would be greatly appreciated. Thanks in advance.

Sounds like a voltage issue with you. Search here how to unlock OBC, then run the voltage test. Monitor your voltage while driving. I have a feeling your voltage regulator is shot, and you get overvoltage.

How old is your battery?

Follow up information
 

Thanks for the very quick reply SlickGT1.

However, I can't drive the car. When I start it, it idles extremely rough...as though it is about to die. I can't rev the engine at all. The accelerator has no effect. I have put a volt meter on it and I'm getting around 13.7 volts when the car is running but it is fluctuating, I am guessing because of the very rough idle. With the engine off, the battery is at 12 volts. I'm checking this by connecting a volt meter to the pos and neg battery connections under the hood...is this correct?

That is fine then, that is where you should be. Hmm disconnect the maf and try again, see how it idles. Did you try scanning for codes?

I haven't tried scanning for codes yet...I have to get a scanner from Advance Auto and they are closed. I'll do that first thing in the morning. I'm going to try disconnecting the MAF as you suggested.

Disconnected the MAF...same thing. Engine Failsafe Prog is displayed. The thing that puzzles me is the unresponsiveness of the accelerator.

I finally figured out how to unlock my OBC on an E53. My voltage is around 11.8 with engine off and between 12.7 and 13.1 with engine idle very rough.

That voltage is not that bad. How old is your battery, and is it OE BMW?

You really need to get the codes scanned.

Oh put your car info in your signature. Helps others advise without reading for an hour. Thanks.

Thanks for the post.

I'm going to pull the codes today and then post them here. Also, I will put my car info in my signature...sorry 'bout that. :-)