DS5 Automatic Transmission Problems

Greetings. I own a DS5 as well, and your description strongly resonates with a past experience of mine. The implausible shifting behavior and emergency mode are particularly telling. When did you last perform a transmission oil change or flush? Often, these symptoms can arise from worn-out transmission fluid, compromising the transmission's ability to function optimally. May I ask, what is the condition of your battery and alternator output?

Thank you for your reply. I haven't actually performed a transmission oil change since I bought the car. I replaced the battery roughly two years ago, but have not performed any diagnostic checks on the alternator output. Would worn transmission oil really cause all of these issues, including the undervoltage reading?

Indeed, deteriorated transmission fluid can manifest in those ways. Its diminished lubricating properties induce erratic transmission behaviour. My experience mirrors yours; although the error pointed towards undervoltage, replacing the transmission oil resolved the problem completely. However, given the undervoltage error, a workshop diagnostic will be required to exclude any potential electrical faults. I recommend visiting a trusted workshop; worn-out transmission oil is the most likely origin.

I appreciate the advice. I took your recommendation and brought the car to a local workshop. They confirmed it was the transmission oil. A complete oil change and flush of the automatic transmission, at a cost of 240€, resolved all of the issues. Now it is shifting smoothly again. Thank you very much!