Espace Overvoltage Errors Resolved

Yes, a heavily discharged or defective battery can absolutely cause overvoltage errors and system failures in your Espace. When the battery voltage drops too low, the voltage regulator in the alternator has to work much harder to maintain the required system voltage. This can lead to voltage spikes and overvoltage situations, triggering those fault codes. The car's ECU is very sensitive to voltage fluctuations. Have you checked the battery's voltage and condition? What voltage are you seeing at idle and under load? It would be helpful to measure that.

I haven't taken specific voltage measurements. If the alternator is overcompensating due to a bad battery, would that explain all the seemingly unrelated system faults?

Precisely. The alternator overcompensating is a common cause of many issues. The voltage spikes can affect various electronic modules and sensors. The weak starting is another symptom. The best approach is to get the battery properly load tested. If it fails, replace it with a high-quality unit suitable for the Espace. Given the complexity, it is best to take it to the workshop if you do not have the tools to properly diagnose the issue.

Thank you for the detailed explanation. I followed your advice and replaced the battery. The garage confirmed it was heavily degraded and the overvoltage is now resolved. Total cost was 290€.