Technical Article • CAN Diagnostics

Understanding CAN Bus Termination

By Keith Fields · Apollo Calibrations

CAN bus communication problems are extremely common in motorsport and standalone ECU installations, especially when multiple devices, aftermarket dashes, PDMs, keypads, or expansion modules are involved.

Improper CAN termination can create intermittent communication faults, unstable device behavior, corrupted data, or complete network failure.

Understanding CAN Networks

CAN Networks Depend on Controlled Signal Behavior.

CAN communication uses differential signaling across CAN High and CAN Low wires.

Because CAN operates at high communication speeds, signal reflections and electrical distortion must be controlled carefully for stable operation.

1. Why CAN Termination Exists

Termination resistors absorb signal energy and reduce waveform reflection.

Without proper termination, CAN signals reflect back through the network, distorting communication.

This may cause:

Intermittent communication loss
Dash dropouts
Corrupted CAN data
Device resets
ECU communication instability

2. Standard CAN Termination Layout

Most CAN networks use two 120-ohm termination resistors.

One resistor should exist at each physical end of the CAN network.

When measured across CAN High and CAN Low with the system powered down, the network typically measures:

~60 ohms = correct dual termination
~120 ohms = only one resistor present
Very low resistance = excessive termination
Open/infinite resistance = missing termination

3. Common Motorsport CAN Problems

Motorsport installations often introduce complex CAN layouts.

Common issues include:

Too many termination resistors
Missing termination resistors
Incorrect device ordering
Excessive stub length
Poor grounding strategy
Incorrect baud-rate configuration

Problems become more common as additional devices are added, especially aftermarket dashes, PDMs, and telemetry modules.

4. CAN Wiring Best Practices

Good CAN communication starts with clean physical layout.

Keep CAN wiring twisted consistently
Minimize stub lengths
Avoid unnecessary splices
Maintain clean grounding strategy
Verify baud rates across all devices
Confirm proper termination placement

5. Diagnosing CAN Communication Faults

Many CAN issues appear intermittently under vibration, heat, or electrical load.

CAN diagnostics typically involve:

Resistance measurement
Oscilloscope waveform analysis
Device isolation testing
Baud-rate verification
Power and ground inspection
Network topology review
Final Thoughts

CAN Stability Depends on Correct Network Design.

Many communication problems blamed on ECUs or dashes are actually caused by improper network layout, poor termination strategy, or wiring mistakes.

Clean CAN architecture becomes increasingly important as motorsport systems become more complex.

Need Help Diagnosing CAN Bus Problems?

Apollo Calibrations provides remote CAN diagnostics, standalone ECU troubleshooting, startup diagnostics, and motorsport technical consulting.

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