Do I Need the 120Ω CAN Termination Resistor?

Every KrispyGauge has a 120Ω CAN termination resistor built in, switched on or off in the Web UI. Whether you need it depends on where the gauge sits on your CAN bus. Here's how to work it out.

The short answer

Try without it first. Most installs don't need it. Only switch it on if you have communication problems.

Why CAN termination matters

A CAN bus is a single pair of wires with a resistor at each end. Those two resistors stop signals bouncing back down the wire and scrambling the data. The bus needs exactly two — one at each end, no more and no fewer.

Most Haltech ECUs already provide one of them, and many have it switched on by default. So the real question is: is something else already terminating the other end?

Where does your gauge sit?

• Spliced into the middle of an existing bus — no resistor. Both ends are already terminated by the ECU and whatever is at the far end.
• The last device on the bus — the ECU terminates one end and your gauge is the other, so it probably needs the resistor.
• The only device on the bus, wired straight to the ECU — try without it first, and switch it on if the data is unreliable.
• Two or more gauges daisy-chained — only the last gauge in the chain gets the resistor. See running multiple KrispyGauges.
• On a car's OBD2 port — never. The car's own bus is already terminated. See OBD2 setup.

Signs of a termination problem

• NO CAN SIGNAL on the gauge even though the wiring is right
• Readings that appear briefly then drop out
• Intermittent readings that get worse with a longer cable
• Keypad buttons that only work some of the time
• RX / TX errors reported by your ECU

That said, check your wiring first. CAN H and CAN L swapped over causes these symptoms far more often than termination does. Yellow goes to CAN High and green to CAN Low — confirm that before you start switching resistors on.

Still stuck? Email [email protected] or ask in the KrispyGauge Tips & Tricks Facebook group.