A CAN bus needs a 120 ohm resistor at each end of the bus, and only at each end. If your ECU already has one built in and the far end of the bus does not, you add one there.
Get termination wrong and the symptom is not a dead bus, it is an unreliable one: data that works at idle and drops out under load, or a bus that works until you add one more device. That is why termination faults take days to find.
How to check:
- Turn the ignition off and disconnect power.
- Measure resistance between CAN High and CAN Low at any point on the bus.
- Around 60 ohms means the bus is correctly terminated at both ends.
- Around 120 ohms means only one end is terminated. Add the second resistor.
- Anything else means a wiring fault, not a termination problem.
The ED Keypad in CAN mode requires a 120 ohm resistor across CAN High and CAN Low.
⚠️ Do not fit three terminators. Adding a resistor “to be safe” when both ends are already terminated pulls the bus down and can stop it working entirely.
Related: CAN Bus Wiring on the E-10 · CAN Bus Wiring on the E-12 · ED Keypad Wiring and Connector Pinout
