I think I remember this problem being discussed here but can not find the thread. On my 2nd Smart, a 2008 Passion I got at the end of 2019, there has been an occasional problem where the starter would stay on after the engine was running. I am a mechanic so I know the difference between the secondary air pump and the starter. This was getting worse so I decided to check it out. I see only 2 possible problems. Mechanical or electrical. I thought I would connect a test light to the starter and run the lamp into the driver's area where I could see it. I backed up on my ramps and looked to see what I would need. I noticed how easy the starter was to get at, so I removed it. Took it apart, cleaned and lubricated everything, put it back in and this solved my problem. In fact the starter sounds better overall.