CAN Bus fault diagnosis — opens, shorts and a node pulling the bus down

CORE TEACHING CAN open circuit; CAN-H short to ground; CAN-L short to ground; short to battery positive; CAN-H short to CAN-L; missing/extra termination; stub faults; corrosion; one transceiver pulling bus down; segmentation through gateways; why a 60 Ω test alone cannot prove every CAN fault. PRACTICAL DEMONSTRATIONS AND TESTS Record healthy waveform; introduce/troubleshoot training faults; compare resistance and scope patterns; disconnect branches/nodes methodically; use topology to identify which modules disappear together. ADVANCED / SCAN TOOL LAYER Scope patterns for open/shorted lines; scan topology; breakout leads; network resistance; optional current-limited fault board. KEY DIAGNOSTIC QUESTIONS Does the fault affect the whole network or one branch? Does unplugging one node restore traffic? Is termination correct? Is one line stuck high/low? MUST-COVER CHECKPOINTS Identify bus/topology; power down correctly; resistance sanity check; key-on voltages only as clues; two-channel waveform; locate affected segment; isolate node/branch.

The whole bus goes quiet when one module is connected. How do you prove whether the wiring, termination or one ECU is collapsing the network?

Builds on

Lesson 35: CAN Bus fundamentals — make the network visible

Feeds into

Lesson 37: LIN Bus — the single-wire network on smart components

1. 35CAN Bus fundamentals — make the network visible
2. 36CAN Bus fault diagnosis — opens, shorts and a node pulling the bus down
3. 37LIN Bus — the single-wire network on smart components
4. 38FlexRay — understanding high-speed deterministic chassis networks
5. 39MOST Bus — fibre-optic infotainment ring diagnosis
6. 40Automotive Ethernet & DoIP — modern ADAS and gateway networks