BITECH Engineering Notes · ~4 min read
You’ve got intermittent CAN errors. Frames dropping, a node that works on the bench and fails in the field. The instinct is to open the logs or reach for a protocol analyzer.
Do this first. It takes 30 seconds and costs nothing.
Why 60Ω
A high-speed CAN bus is a twisted pair with a 120Ω terminator at each physical end — they absorb the signal so it doesn’t reflect back and corrupt frames. Two terminators, one at each end, no more, no less.
Those two 120Ω resistors sit in parallel across CANH/CANL. Two 120Ω in parallel = 60Ω. So measuring resistance across the bus tells you whether both terminators are actually there.
The check
- Power off the system. Not optional — active transceivers skew the reading. On a vehicle, let the network sleep or disconnect the battery negative.
- Set the multimeter to resistance (Ω).
- Measure between CANH and CANL (on a vehicle: OBD-II pin 6 and pin 14).
- Read against the table below.
| Reading | What it means |
|---|---|
| ~60Ω | Healthy — both terminators present |
| ~120Ω | Only one terminator — the second is missing or open |
| ~40Ω | A third terminator is installed — remove the extra |
| ~0Ω | Short between CANH and CANL, or a wiring fault |
| very high / fluctuating | No termination, or an open in the harness |
A few ohms off 60 is normal — cable, connectors, and transceiver impedance all nudge it. You want “close to 60,” not a lab number.
What it does NOT tell you
This is where people get a false sense of safety. A resistance check confirms the total termination — nothing more:
- •It can’t confirm placement. ~60Ω could be two correct end terminators, or a single 60Ω resistor in the middle, or terminators on the wrong nodes. Only physical inspection confirms they’re at the true ends.
- •It can’t see software-switched terminators. Some devices enable termination after power-up — invisible to a cold resistance test. Check the manual.
- •It won’t reveal shorts to ground or supply — those need separate CANH/CANL-to-ground and -to-power measurements (should read megohms).
- •It won’t show the waveform. Bit timing and reflections still need a scope or CAN analyzer. The 60Ω check just tells you whether it’s worth reaching for one.
Why it’s worth the 30 seconds
A missing terminator is the classic trap: a bus with only one terminator often works temporarily, then turns unreliable and fails — usually after it’s already in the field. Catching it at 60Ω on install is a lot cheaper than catching it at 2 a.m. on a customer’s line.
And the rule travels: EV/BMS packs, AGVs and AMRs, robots, industrial controllers — anywhere CAN runs, 60Ω is the same first clue.
The takeaway
Before the oscilloscope, before the analyzer, before the logs: power off, measure CANH–CANL, check it’s near 60Ω. If it isn’t, you’ve found your problem before wasting an hour on software that was never broken.
At BITECH we build industrial and edge-AI computers with native, hardware-level CAN / CAN FD controllers — not USB-CAN bridges — and 4000V-isolated CAN where the deployment needs it, so the physical layer is sound before termination even enters the picture.