CAN Bus fundamentals — make the network visible

CORE TEACHING Why vehicles use networks; CAN nodes; CAN High and CAN Low; differential signalling; dominant/recessive states; twisted pair; termination resistors; typical ~60 Ω whole-network check when correctly powered down; common high-speed and medium-speed networks; gateways; message IDs conceptually; why voltage numbers vary by architecture and must be checked against service information. PRACTICAL DEMONSTRATIONS AND TESTS Find a CAN pair on a vehicle/training loom; key-off resistance check under correct conditions; key-on DC voltage sanity check; two-channel scope of CAN-H and CAN-L; identify a healthy differential waveform. ADVANCED / SCAN TOOL LAYER Two-channel scope; scan topology; gateway module list; decode only at a high conceptual level — the aim is physical-layer diagnosis first. KEY DIAGNOSTIC QUESTIONS Is the network physically intact? Is resistance plausible? Are both lines switching? Are the missing modules all on the same bus segment? 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.

Several unrelated modules show ‘no communication’ after one wiring fault. Before replacing modules, understand what the two twisted wires are actually doing.

Builds on

Lesson 34: Wipers, park circuits and intelligent motors

Feeds into

Lesson 36: CAN Bus fault diagnosis — opens, shorts and a node pulling the bus down

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