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BMW X3 Trailer Towing – Electric Brakes?

April 5, 2010

Q
car year: 2007
car model: X3 3.0si
I would like to install an electric trailer brake controller on my ’07 X3. I have received conflicting information on whether or not this would interfere with the brake light monitoring system possibly sensing a failed brake light and/or the braking system as a whole. If this will not interfere would you have a recommendation on a compatible controller?

A
We have not experimented with installing electric brake controllers on the X3 (or the X5). Since the controller does piggy-back on the brake light switch circuit, there is a chance that it could confuse the Check-Control system and cause it to generate a brake light fault. However, it may be fine. BMW does state that the Active Stability System will work in concert with the trailer, when towing. I would think that you could test it by temporarily wiring the controller’s input wires to the brake light switch wires, prior to a full install of the system.

With the above points made, I am wondering what you are towing, with an X3, that would have electric brakes (versus surge brakes). The BMW X3 hitch assembly is a Class-II hitch. This means that the maximum towing capacity (of the hitch) is 3500 lbs, with a 300 lbs tongue weight. This would typically be covered with surge brakes on the trailer. One exception is that many car trailers are supplied with electric brakes. If this is your case, simply do the temporary install of the controller to see if it affects the Check-Control system.

If you do this test …… let us know what you find so we can share it with other X3 and X5 owners.

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