Good morning, today we present a case reported by electrician FANTINI FABIANO MIRKO who kindly informed us how he solved a somewhat thorny case.
The car in question had a battery warning light in the instrument cluster despite the alternator charging correctly at 14 volts.
In diagnosis, the only error was as follows:
B120F-81 the alternator component has a fault.
Even when replacing the alternator, the fault recurred.

Small parenthesis: checking the circuit diagram, the only component between the alternator and the SAM control unit appeared to be a U470 (original circuit diagram attached). It was thought to be an intermediate junction box that could interrupt the signal. It later emerged that this was not a physical electrical component, but simply a description given by the parent company to identify which version of the vehicle the wiring diagram might fit. In this case it referred to the entire Smart 453 model.

After several days of testing, the solution was found: the garage that took the car to the electrician had not said that they had replaced the engine complete with wiring. Basically, the engine plug that plugs into the passenger compartment socket has a different pin position (perhaps due to some wiring modification) and the alternator's LIN line did not correspond with the pin of the LIN cable that goes to number 18 on the driver's side SAM control unit.
It was enough to move the pin of the plug to its corresponding pin and the fault no longer recurred.

I would like to thank the workshop again for the valuable report, hoping it will be of use to you, and on behalf of the Technical Help Desk team I wish you good work

• SMART-FORFOUR-453-1.0-dal-11-2014-in-poi-281920-AVVIAMENTO-E-RICARICA-SCHEMA-ELETTRICO (EN - translation in progress, please try again in a few minutes)