A brief Noobie and Old timers how it works guide to your W220 and other MB's
Your Car is a rolling Computer Network !!
In case you didn't realise, they really don't work like other Marques of the period, everything is controlled via CAN Bus, Switches send a Computer (CAN Bus) Signal to another Module which then applies Power to the item ...........
A Bulb, a Motor, a Solenoid .......... whatever !!
A wonderful piece of Engineering which back in the W220's era was way advanced for it's time.
However, it does not work like, (for example), a 2002 Model Year Ford, Toyota, GM, Honda etc
For example, your Central Locking (C/L) is operated by Radio Frequency (RF) Signal from Key Fob or Infra Red (IR) for Global Opening / Closing, which then goes via Antenna Amplifier or Door Handle IR Receiver to Communication Area Network Wires (CAN Bus) tells Electronic Ignition Switch (EIS) the Key's command, which then goes via CAN Bus to the Pneumatic Systems Equipment Pump / Controller (PSE) and other Modules like Alarm (ATA) and Signal Acquisition Modules (SAM's) which converts the button press to a Vacuum or Pressure, that is then sent via Pneumatic Lines to Doors, Trunk Lid etc The Alarm (ATA) switches off / on, and sends a signal over CAN Bus to Left and Right Front SAM's and Rear SAM, which switches the Indicators Flashing ...........
This system applies to almost everything on the Car, you turn the Light Switch, Wiper Switch, Press Throttle, Move Gear Selector, Open Door, Press Sunroof or Window Buttons, Press Rear Window Blind Button etc etc etc and off goes a CAN Bus Signal to various Modules !!
The EIS on Pre Facelift Cars, or Central Gateway Module (CGW) on Post Facelift Cars acts as a Router for these CAN Bus Signals.
For this reason, I suggest getting the Star Diagnostic System (SDS), which can be bought (clone), from £399 upwards these days as a Plug and Play set up.
SDS will pay for itself and save you a fortune over a few years of ownership !!
It is as essential as Spanners, Sockets and Screwdrivers for an awful lot of Diagnosis and Repairs on these Cars.
also save you spending a lot of time and money trying to diagnose a problem by substitution, which often doesn't quite work out because many modules need to be Version Coded with SDS, also SDS contains Testing and Live Data facility, Guided Diagnosis plus all the Workshop Manuals and Wiring Diagrams (WIS), Parts Catalogues (EPC), Component Locations (Star Finder) etc etc.
Don't let anyone else tell you that any other diagnostic tool will do all you need, IT WILL NOT !!
Almost all the others are just Code Reader & Re-Setters that do not access all Codes in all Systems