Master ECU Implausible Signal

It definitely sounds like a software glitch with your Renault Master's ECU. The symptoms you're describing – error code, electrical malfunction, and navigation failure – strongly point to that. The error code stored is key here. Without knowing the exact code it is difficult to be 100% sure, but the programming of the control unit being implausible is likely. Has the vehicle had any recent maintenance or software changes prior to this? Have you tried a simple software reset by disconnecting the battery for 30 mins?

I haven't had any recent software changes that I know of, and to be honest, I'm a bit nervous about disconnecting the battery in case it messes something else up. When you say 'programming of the control unit being implausible' what does that actually mean? Is recalibration something I can do myself, or is it a garage job?

By 'programming of the control unit being implausible', I mean the data or instructions stored within the ECU's memory might be corrupted or inconsistent, causing it to misbehave. While a software reset might help, given the potential complexity and the value of your van, I'd really suggest you take it to a reputable workshop with Renault diagnostic equipment. They can properly read the error codes, pinpoint the exact cause, and safely recalibrate or re-flash the ECU if necessary. Better safe than sorry!

Okay, that makes sense. I booked it in with a local garage who ran diagnostics. Turns out it was an implausible signal from the ECU, costing 240€ to recalibrate. All sorted now!