CAN Bus & Vehicle Networks

8 Lessons

How CAN, LIN, FlexRay, and Ethernet work. Read U-codes, measure termination resistance, scope CAN waveforms, and isolate network faults systematically.

Overview

Modern vehicles have 50+ electronic modules communicating over multiple network buses. This module covers CAN bus physical layer fundamentals, differential signaling, termination resistance, LIN bus for body systems, FlexRay for safety-critical applications, and automotive Ethernet for ADAS. Learn to read U-codes, measure CAN-H and CAN-L voltages, diagnose with a scope, and isolate faults using a systematic network diagnosis workflow.

Key Components

CAN-H and CAN-L wires (pins 6 and 14 at DLC)
120-ohm termination resistors
Gateway modules
LIN bus master/slave devices
Network wiring diagrams

How It Works

CAN bus uses differential signaling on two wires — CAN-H rises to 3.5V while CAN-L drops to 1.5V during transmission. Both idle at 2.5V. The voltage difference carries data, and the twisted pair cancels electromagnetic noise. Termination resistors (120 ohms each) at each end prevent signal reflections. Two resistors in parallel should read 60 ohms at the DLC with key off.

Common Problems

Corroded connectors and splice packs causing communication loss
Water intrusion in modules
Chafed CAN bus wiring shorting H to L
Failed termination resistor (reads 120 ohms instead of 60)
Security gateway blocking aftermarket scan tools

Diagnostic Tips

Always check DLC pins 6 and 14 for 60 ohms termination resistance first
U-codes across all modules usually mean a bus problem, not individual module failure
Check module power and ground BEFORE blaming the network
Disconnect modules one at a time to isolate a shorted node
Use dual-trace scope on CAN-H and CAN-L for mirror-image waveform verification

Diagnostic Tools

These guides cover the advanced tools used to diagnose can bus & vehicle networks faults in the real world.

Skills

PicoScope Automotive Diagnostics

Waveform analysis for sensors, actuators, and serial data. The scope does not lie.

Skills

Thermal Camera Diagnostics

See heat patterns, find failing components, and verify repairs without disassembly.

Study with an AI Instructor

Pro members get an AI vocational instructor that teaches alongside every lesson. Ask follow-up questions, break down concepts, and study together like having a master tech sitting next to you.

Related Systems

Hybrid Vehicles

11 Lessons

Hybrid powertrains, regenerative braking, high-voltage safety, and service procedures.

Basic EV Theory

7 Lessons

Electric vehicle architecture, battery management, charging systems, and the future of service.

Diesel

8 Lessons

Diesel engine operation, common rail injection, DPF, DEF, and diesel-specific diagnostics.

Disclaimer: APEX Academy content is for educational purposes only and is not a substitute for manufacturer service information, OEM repair procedures, or professional training. Specifications, procedures, and technical details vary by manufacturer, model year, and application. Always verify information against the manufacturer's service manual and current TSBs before performing repairs. APEX Tech Nation and A.W.C. Consulting LLC are not liable for errors or for any outcomes resulting from the use of this content.