WIS 54.00 General

CAN (Controller Area Network)

The W220 has two separate CAN (Controller Area Network) Bus systems.

• CAN C - Engine CAN (also known as Chassis CAN). Fast communication speeds 125 kbps or 500 kbps.
• CAN B - Interior CAN (also known as Body CAN). Communication speed 83 kbps.

What is a CAN (Controller Area Network) Bus

• A digital communication link between multiple Electronic Control Modules (ECM).
• A two wire, bi-directional communication link with data transmitted according to priority.
• Provides message specific addressing.
• 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. Also if one wire becomes faulty the signal should still get through. When both CAN H and CAN L signals are faulty no communication is possible.

Example of W220 CAN B

The CAN B or Interior CAN is also known as Body CAN.

Diagnosing CAN Faults

M-B 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. (Be careful of causing electrostatic damage to electronic components.) Typical W220 CAN Bus Connector (note wire pairs).

Typical W220 CAN Signal Levels

• 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.