Peugeot 106 Automatic Gearbox Problems

I had very similar symptoms with my 106. The automatic transmission was slipping, and the shifts were rough. I'm not convinced it's necessarily 'undervoltage'. How old is the transmission fluid? When was the last time you had it changed? That's always the first thing to check.

I haven't changed the transmission fluid since I bought the car a few years ago. I'm not sure when it was last changed before that. Could old transmission fluid really cause all these problems – the slipping, the light, and the emergency mode?

Yes, absolutely. Old, degraded fluid loses its lubricating properties and can cause all sorts of havoc in an automatic transmission. While a fluid change might not solve underlying mechanical issues, it's the cheapest and easiest first step. If changing the fluid doesn't fix it, you are probably looking at a visit to a workshop.

I had the automatic transmission oil replaced at the workshop, and it seems like that solved the issue. The shifting is smooth again, and the transmission light is off. The mechanic confirmed the old oil was in a terrible state. The total repair cost was 240€ which is acceptable. I really appreciate your help!