71 00... Notes On Retrofitting A Trailer Towing Device
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Starting with delivery of the E90, in certain vehicle types, the size of the electric cooler fan will be linked to the optional extra trailer tow hitch or trailer provision.
A larger fan may therefore be required for retrofits.
The larger fan is necessary to ensure mountain driving with a full trailer load in accordance with BMW-internal specifications. Otherwise the engine electronics will detect possible overheating of the cooling system and activate protective functions.
For the customer, this involves impaired A/C output, automatic transmission and engine power. These will be continuously reduced, which in the end may result in the vehicle coming to a standstill in the mountain area.