Immobilizer (theft control unit) replacement question
 

Ok, so has anyone ever replaced a bad Immobilizer unit (theft control unit). I am getting conflicting account on whether or not a used one can be used. some say it should just plug in and be fine (paired to the key) other say it has to be programmed to the car and that once programmed to one car you can't re-use it.
I have noticed that most of the used ones on eBay come with the ECU, keys and door, ignition and even glove box locks. and even they state that it may have to be professionally programmed.
insurance is paying for it to be replace, but I would rather do it myself and save the $500 deductible. if I have to pay $600-$700 for the part, and another several hundred to have the dealer code it. I may be out more than that.

Short answer, yes a matching set from a similar year/model will work. I put one in my 01 and everything functioned. The long answer is a bit more complicated. There will be some info in your DME that will be incorrect without reprogramming.

did you replace your DME as well? if not, did that effect how the car ran, throw any codes etc...?

The DME has to be programmed to accept and work with a different immobilizer.

Yes, if you go this route, you have to replace the CLU/immobilizer box, key (fob with transponder), and DME. The set you get all need to be from the same car and the same DME version as your car.

If your deductible is $500 and your insurance will pay for a new immobilizer? I say take that deal! I sell a used immobilizer,DME,locks and key for $350. For $150 more you're getting a brand new immobilizer and reprogramming at the minimum from your insurance company. Heck you might get new key fobs and a DME out of the deal too. Consider yourself lucky though(that's if you like your boxster), a lot of insurance companies write off Porsches with wet immobilizers. Sometimes a wet immobilizer can take a lot of other electrical components down with it.

The DME, transponder (the little "pill" inside the key fob), and immobilizer all have to be programmed as a set. If you replace any single component of the set, then that component has to be re-programmed to work with the other two components.

It is often easier and cheaper to buy a replacement set of all three components and swap them all at one time.

You will also have to swap the key shank from the "old" fob to the "new" fob so the "new" fob will mechanically unlock the steering wheel lock.

I two complete matched sets and swap all three components (as sets) often in my Spec Boxster race car.

It is also possible to transfer the information directly from the old damaged alarm/immobilizer module to a new or used module. You do not need to replace the key transponders or reprogram the ECU/DME. BTDT. Note that this is NOT something a dealer has the proper tools to do.