From DISCO3.CO.UK Knowledge Base
Before unplugging any connectors or for Hard Reset
If you're going to unplug any vehicle connectors, make sure you disconnect the battery first, otherwise the vehicle will register loads of 'faults'
The procedure is:-
- To avoid any chance of being locked out of the vehicle first lower the driver's window then remove the key, close all doors, including the tailgate - although you'll need the bonnet (hood) open - don't lock the vehicle though.
- Wait a minimum of 2 minutes, then check through the window that the park brake warning light, NAV screen & clock display are all off.
- Remove the -ve terminal first, making sure that it can't spring back to the battery, then remove the +ve terminal.
- For a hard reset: Protect the exposed battery terminals with plastic caps or a rubber mat then short the Positive & Negative CABLES only together. If they won’t reach each other use a jumper wire or, less desirably, grab a screw driver & place across the ends of the cables...REMEMBER not to short the BATTERY TERMINALS. Leave shorted cables connected together for a minimum of a minute to discharge capacitors etc.
- CAUTION: MY14 vehicles and later with Stop/Start have an additional battery fitted; the implications of this for the hard reset technique are not fully understood.
- Do whatever you need / want to do / or wait 5 -10 minutes for Hard Reset.
- Replace the +ve terminal, ensuring it is properly seated at the base of the tapered terminal so it cannot be moved once re-torqued.
- Refit the -ve terminal, ensuring as far as possible that it makes good contact first time, you may get a small 'arc' as the terminal contacts the battery, nothing to worry about, it's just the vehicle 'waking up'. If it's a good flash and the insulation turns to liquid plastic..... use a tool - not your hands - and remove the -ve terminal as fast as you can, for something is badly wrong.