This is a brief outline of typical CAN networks in vehicles and what the rules are about how to modify them.

A Typical CAN Network

This network has three electronic control units (ECU's), and a termination resistor at each end.  The wiring between each ECU and the main network is called a stub.

Note that all CAN networks should follow these rules:

  • Stub distance should be short, <20 cm.

  • Distance between nodes/ECU must be >10 cm.

  • Distance between nodes and resistors can be Ø cm.

  • There are two 120Ω resistors, one at each end of the CAN network.

Variations

In some cases, the termination resistors are inside of an ECU, as shown in this example:

  • Commonly in factory vehicles, the resistors are inside nodes/ECUs.

  • The total length of the CAN network can be long, up to 40 meters.. 

  • Adding additional nodes along the CAN network is possible following Steps 1-4 (shown below). 

Adding an ECU to an Existing CAN Network - Step 1


  • Cut CAN network cable.

Adding an ECU to an Existing CAN Network - Step 2


  • Add plugs.

  • Add plugs to cut terminal ends of wire. As a rule pin 1 is “high” and pin 2 is “low.”

Adding an ECU to an Existing CAN Network - Step 3

  • Create extension by adding length of wire with matching plugs, stub, and additional ECU.

  • Creating additional length of wire with a short stub to a node/ECU will omit interference in BUS network.

  • If stub is too long, there will be interference. The stub must be short, stub length can be Ø.

Adding an ECU to an Existing CAN Network - Step 4

  • Connect plugs of extension and of original CAN network to complete the addition of an ECU to an existing CAN network.