CAN-bus Wiring

CAN-bus Wiring Made Simple

What is CAN-bus?

CAN-bus (Controller Area Network) is a system that allows different devices in a vehicle (like ECUs) to communicate with each other. It uses two wires: CAN High (CAN H) and CAN Low (CAN L).

Is CAN-bus Important?

When conducting an M57 engine conversion, the CAN-bus plays a critical role in ensuring your conversion works properly. Here’s why it’s essential:

  1. Diagnostics:
    Even if you’re running a manual conversion, some diagnostic tools require a properly terminated CAN-bus to function. Adding termination resistors (120 ohms at each end) is often necessary for diagnostics to work correctly.

  2. Engine-to-Gearbox Communication:
    The CAN-bus enables communication between the engine and the gearbox. Without this connection, the transmission will not operate as intended.

  3. Integration with Other Modules:
    The CAN-bus also facilitates communication with other modules, such as dashboard controllers or displays, ensuring everything works seamlessly together.

So, when people ask, “Is CAN-bus important?” the answer is clear: It’s absolutely critical if you want your conversion to function properly.

Basic Wiring Rules

Imagine that you are wiring things in parallel, it is the same here. The only difference is that the wiring is twisted.

  1. Connect All CAN High Wires Together:
    All the CAN High wires from your devices must be connected to each other.
  2. Connect All CAN Low Wires Together:
    All the CAN Low wires from your devices must be connected to each other.
  3. Twist the Wires:
    The CAN High and CAN Low wires should be twisted together. This helps reduce interference and ensures reliable communication.
  4. Add Termination Resistors if required:
    • The CAN-bus needstwo 120-ohm resistors.
    • These resistors ensure the bus works properly by preventing signal reflections.
    • The total resistance of the bus should be 60 ohms.

A simple CAN-bus circuit with 2 nodes would look like this:

CAN-bus Wiring House of Torque

3 nodes would look like:

CAN-bus Wiring House of Torque

And so on…

How to Check the Resistance

  1. Turn off all devices connected to the CAN-bus.
  2. Use a multimeter to measure the resistance between the CAN High and CAN Low wires.
    • If the reading is 60 ohms, the bus is correctly terminated.
    • If the reading is 120 ohms, you need to add a second resistor.
    • If the reading is 0 ohms, there’s a short circuit in the wiring.
    • If the reading is infinite, there are no termination resistors.

Quick Tips

  • Use twisted-pair wiring for CAN High and CAN Low.
  • Keep the wires as short as possible.
  • Make sure the total resistance of the bus is 60 ohms.