Repairing vehicles without locking up the radio antitheft system

I want to start repairing cars that don't belong to me. Many car owners are not aware that disconnecting the battery power for any reason will lock up the radio antitheft system, so they often don't have the code readily available. Since it is safe practice to disconnect the battery first, how can I change common items like sensors, alternators, starters, etc. without locking up the car owner's sterio? How does a small garage operate? Do they register with the dealers in some way? Anybody got any info?

Thanks, RepairJunkie

Most manuals state that power should be disconnected before plugging/unplugging sensors. Is this a common practice for small garages? Do they use a 9V battery in the cigarette lighter?

I had a battery changed at the Advanced Auto parts and they have a full sized car battery that plugged into the cigarette lighter. Said they are required to do it on all newer cars to prevent ECU failures.

Cecil

Starting around late 1999 or early 2000 the VW radios pick the code from the cluster. That if the radio was never replaced!

This all makes sense for changing the battery, but not for the starter or alternator because you can easily cause shorts and definitely not for sensors because plugging/unplugging when they are getting powered thru the cigarette lighter can damage the computer. It depends on whether the computer's sensor amplifier (an In-Amp) is overload protected. I am speaking from the perspective of an electrical engineer, but someone much more familiar with common practices in the auto industry can probably tell me what's really going on. In any case I'll speak with Advanced Auto. Thanks!

Unless -- with the key in the accessory position -- the radio and cig.lighter are energized and the ECU (computer) are disconnected from the circuit. This would keep power to the radio, but removing the (underhood) battery would cut power to the ECU, thus allowing sensors, alternator, starter, etc. to be plugged/unplugged safely. Anybody know if this is true and where I can find a tech. write-up on it?

I had my battery changed twice in 3 years on my 1999 Passat with no external power connected to the car VW cars compare the code on the wireless with the remembered wireless code stored in it's control unit if it's the same then no problem, if the wireless is replaced then you need the code for that wireless.

Thanks so much! Finally found it. Do a Google search on " auto memory saver" and it comes up all over the place.

Thanks to all who helped!

Thanks so much! Finally found it. Do a Google search on " auto memory saver" and it comes up all over the place.

Thanks to all who helped!