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Steve, BMW Expert
Category: BMW
Satisfied Customers: 24119
Experience:  BMW Expert
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My rear window defroster (no light) would work..blower fan..low speed

Customer Question

I own a 2007 Z4 and several months ago my battery ran down due to leaving my radar detector pluged in. The bettery was several years old so I replaced it. After words neither my A/C (no snow flake light) or my rear window defroster (no light) would work and also the blower fan would only work in very low speed. I did replace the blower resister (didn't fix anything! I have read that the computer will shut these systems off when low voltage is sensed or it may have been put in "transport mode" which will deactivate the A/C. If this is true how do I reset the computer? I am an aircraft mechanic so I just need to know how!! Also before the battery problem everything worked perfect. Thanks , Mike
Submitted: 6 years ago.
Category: BMW
Expert:  Steve replied 6 years ago.

Hello and welcome to JustAnswer BMW,

My name is XXXXX XXXXX it will be my pleasure to assist you today.


This is a very complex system and if the car has gone into transport mode (which it may have) the only way to get it out is with dealer equipment.


The one thing you can try at this point, is to unhook the car's batter for an hour. This will do a hard reset of all systems and can sometimes clear out strange computer faults.


If the battery reset does not work, the car will unfortunately need to be seen by BMW as dealer equipment is required to interface with these systems. No matter how technically capable a person is, it is simply impossible to reset this without a BMW diagnostic computer.


The only other possibility besides transport mode would be an internal fault with the heating/AC system - which again will unfortuately require dealer equipment to diagnose.


BMW does not make it easy to work on these vehicle's electronics at home, or even for independent mechanics for that matter.


I am sorry I cannot have better news for you, but this is the reality of the situation, and is a complete and accurate answer to your question.


I hope that is helpful, please let me know if you have further questions, or if I can clarify anything for you.


It has been my pleasure to help today and I wish you the best of luck with the vehicle.


If satisfied with my assistance, please press the green ACCEPT button so that I may be credited for helping today. I am not credited or compensated whatsoever until you press the green ACCEPT button.




Many thanks.



Steve and 4 other BMW Specialists are ready to help you
Customer: replied 6 years ago.
I have read that you could run some of the test fuctions and troubleshooting without the diagnosis testor? It requires to run the test functions with "terminal R ON" which is the #1 position of the key, however it then says to also have "terminal 15 ON" how do you do this? What is terminal 15? Shouldn't I be able to reset the electrical or transport mode this way? Thanks, Mike
Expert:  Steve replied 6 years ago.

No, you need the dealer computer.



Customer: replied 6 years ago.
I tried the hard reset with the battery disconnected for an hour, no luck!! I guess I will take it over to the dealer, do you have any idea what this is going to cost me? I appreciate your help with this problem. Mike
Expert:  Steve replied 6 years ago.

My pleasure Mike.


If it is just a programming glitch or transport mode, probably an hour of labor. If there is a problem with the climate control system, it could run several hundred. Let's hope it is just transport mode.


Best of luck.