BSS stands for Bit Synchronous Single Wire. There are 3 different BSS signals. The difference between them is the ability to show different alternator errors: BSS-1 = only shows a mechanical or an electrical error BSS-2 = only shows a mechanical or an electrical error BSS-3 = only shows a mechanical and electrical error
It is not possible to interchange BSS-1 and BSS-2 regulators with each other because the car ECU can ask about a certain error and if it doesn't get the right answer, it will show an alternator error (charging lamp on) on the dashboard. BSS-3 can be used for BSS-1 and BSS-2 because it is universal (BSS-3 can provide information about both errors). BOSCH voltage regulators are all BSS-3, so you never have to interchange it with another regulator. Caution should be taken with VALEO regulators, because they came in 3 different options: BSS-1, BSS-2 and BSS-3. From our experience we know that it is impossible to purchase new VALEO BSS-3 Regulators for now.
For example, on the BMW E60 series cars from 2003 and up there is a Valeo TG17C010 alternator mounted that has a BSS-2 system onboard. Some years later they used the same alternator, but its number is replaced by the TG17C048 which has a BSS-3 regulator. If you order a Valeo voltage regulator for that particular alternator you will receive a BSS-2 regulator. If you purchase a new TG17C048 alternator, it will be equipped with a BSS-3 regulator.
We have checked the signal coming from the ECU on a BMW E60 that had the TG17C048 (BSS-3) OEM alternator, but it was BSS-2. Probably the BMW factories are getting ready to upgrade the protocol into BSS-3, but for now they just equip the cars with BSS-3 alternators. Most probably the BSS protocol will no longer be developed, as they will be using the new LIN-INFINEON in the future.
Same situation is with BMW TG17C034 and VW TG17C020: OEM comes with BSS-3, aftermarket BSS-2 and it should work without any problems. In such situations we will advise to order the one of the Valeo voltage regulators and check if it is really a BSS-1, BSS-2 or BSS-3 regulator. This way you will know for sure and you could mount that specific BSS regulator on that alternator. This way you don’t need to have many different regulators for every different BSS alternator.