- what exactly can i do with the hidden menu? what is its purpose?
- how can i have access to it?

you can look at some details of the car's data, actual speed,volts , fuel remaining in L, average mileage/ week, water temp, fault codes...... the list just goes on.
can be access by key in ignition, press the 0.0 button until the screen show something different, then scroll to 19 by pressing the 0.0 button, enter the lock code (sum of last 5 digit of VIN)


hope this helps

I"ve tried the same thing but nothing happens - the lock won't seem to go off and I can't access anything (except menu 2.0, which tests the gauge cluster).