There are two types. The first is a basic unit which records outside temperature, time date and has an ice warning. The second has all this plus a load of other features such as fuel consumption, range etc. Be very careful about retrofitting an OBC to your car, especially if you don't already have one. 520i models did not have OBC's as standard and retrofitting one is dependent upon whether the wiring harness exists. This is one feature that changed between models. The next hurdle is the in dash fitting which requires the plastic unit to be installed, otherwise its an expensive item from BMW. Next is to see whether you have the wiring to link to the outside temperature sensor. Suggest you may not. Finally, you need a coding plug to fit to the rear of the instruments to make it all work. Frankly, unless your'e rabid about having one, suggest you have a long think about it. I have the basic OBC on my car and went through this exercise myself. Needed an OBC that matched the car (and whilst they all fit some don't, especially some from early E32 models), the the coding plug and finally the new insert. Couldn't be bothered in the end even after I had pulled it all out check in and tested an OBC to make sure. Unfortunately, 520i models really got the short stick when it came to advanced features.
Hope this helps,
Geoff
Sydney, Australia
'94 525iA
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