WIS 82.90 On-board Communication System, Multi-function Steering Wheel
CAN (Controller Area Network)
Description - CAN (Controller Area Network)
The CAN (Controller Area Network) Bus is a digital computer network which provides:
- A digital communication link between multiple Electronic Control Modules (ECM).
- Provides message specific addressing.
- A two wire, bi-directional communication link with data transmitted according to priority.
- The two wire (CAN H and CAN L) method ensures that any interference picked up in the wires is common to both CAN H and CAN L signals and is not "seen" by the receiving module.
The W220 has two separate CAN (Controller Area Network) Bus systems.
- CAN C - Engine CAN (also known as Chassis CAN) which has fast communication speeds of 125 kbps or 500 kbps.
- CAN B - Interior CAN (also known as Body CAN) which has communication speeds of 83 kbps.
Example - W220 CAN B Network
The CAN B or Interior CAN is also known as Body CAN.
Issues - CAN (Controller Area Network)
- If one wire becomes faulty the CAN signal should still get through.
- If both CAN H and CAN L signals are faulty no communication is possible.
Diagnosing - CAN (Controller Area Network)
Using the STAR DAS is the best method to diagnose CAN function.
Alternatively, for simple analysis, CAN Signal Levels can be measured using an oscilloscope with respect to 0V or Ground or differentially between CAN H and CAN L at any CAN Bus Connector.
Warning! Be careful of causing electrostatic damage to electronic components.
CAN-BUS distribution blocks
(Note wire pairs)
W220 has CAN distribution blocks in three locations:
- X30/4 - Right voltage distributor (CAN) connector
- X30/5 - Left voltage distributor (CAN) connector
- X30/6 - Cockpit voltage distributor (CAN) connector
To detach connectors the block cover has to be removed. Insert a flat head jeweler's screwdriver to lift the latches on each side. It helps when you use masking tape to tape the screwdrivers to the side of the block to prevent the jeweler's screwdrivers from falling off. Then gently pry off the cover (upward) with another small flat head screwdriver. It's better to pry off from one end and then the other.
Typical Signal Levels - CAN (Controller Area Network)
- CAN H (High) steady 0.025V when the CAN Bus is dormant (not communicating) and,
- CAN H (High) 0.65V amplitude when the CAN Bus is communicating.
- Signal data for CAN H is a voltage level going high.
- CAN L (Low) steady 11V when the CAN Bus is dormant (not communicating) and,
- CAN L (Low) 4.65V amplitude when the CAN Bus is communicating.
- Signal data for CAN L is a voltage level going low.
Central Gateway (CGW/ZGW)
The firmware of Central Gateway (including CAN System Diagnosis interface) can be updated using SDS under "CGW - Central gateway -> Control unit adaptations -> Control module programming". However, since the update process goes online to pull latest firmware version the procedure can be done only by the dealer using their Star Diagnosis machine.
The latest CGW software version available for A2115403545 (checked April 2015) is 12/2003 (CGW Diagnosis identifier SDS Diagnosis identifier 1/2).
Software Version in SDS
Software version can be read in SDS under "CGW - Central gateway -> Control unit version" and "System diagnosis (only interior CAN fault) -> Control unit version".
Software Version in SDS Quick test log
SDS initial quick test log will display CGW and System diagnosis software version.
Using STAR SDS to Access CGW Items
Developer Mode in STAR is in German because its meant for factory techs only. It allows delving into factory level settings/programming on about everything in the car. You can do some interesting things, but be warned, you can make your car a smoking hole too.