Vehicle communication field guide
NETWORK
DIAGNOSTICS.
Map the topology. Prove the physical layer. Then move up the stack.
Voltage, termination and topology differ between network types. Identify the exact network before connecting test equipment.
High-Speed CAN / CAN FD
Powertrain, chassis, safety and gateway communication
Twisted pair: CAN High and CAN Low
Typically 500 kbit/s; CAN FD data phase may be faster↗02Low-Speed / Fault-Tolerant CAN
Body, comfort and convenience networks on many platforms
Twisted pair with transceivers designed to communicate after certain single-wire faults
Commonly up to 125 kbit/s↗03Local Interconnect Network
Doors, seats, mirrors, climate actuators, alternators and smart sensors
Single wire pulled toward battery voltage; dominant state is low
Up to 20 kbit/s in normal LIN operation↗04FlexRay
Deterministic chassis, powertrain and safety communication on selected platforms
Differential pair per channel; Channel A and optional Channel B
Up to 10 Mbit/s per channel↗05Automotive Ethernet
ADAS, cameras, infotainment, gateways and zonal backbones
Single-pair full-duplex Ethernet with specialized automotive PHYs
10, 100, 1000 Mbit/s and higher depending on BASE-T1 standard↗06MOST Multimedia Network
Legacy and premium infotainment, audio amplifiers, displays and media devices
Plastic optical fiber, unshielded pair or coax depending on system
25, 50 or 150 Mbit/s by MOST generation↗07ISO 9141 / K-Line
Legacy diagnostic communication between modules and scan tools
Single K wire referenced to vehicle battery and ground; optional L line on some systems
Low-speed serial communication; implementation varies↗08SAE J1850 VPW / PWM
Legacy GM and Ford module communication
Vehicle-battery-referenced bus wiring
10.4 kbit/s VPW; 41.6 kbit/s PWM↗09ISO 15765 CAN Diagnostics
OBD-II diagnostic transport over CAN
CAN High and CAN Low
Typically 250 or 500 kbit/s↗10Diagnostics over IP (DoIP)
Ethernet-based vehicle diagnostics
Shielded or unshielded automotive Ethernet twisted pair
100BASE-T1 or 1000BASE-T1 depending on platform↗11SENT Sensor Protocol
High-resolution one-wire sensor data
Single signal wire with power and sensor ground
Nibble timing defined by the sensor tick period↗12PSI5 Safety Sensor Network
Digital airbag and safety sensor communication
Two-wire powered interface carrying supply and data
Typically 125 or 189 kbit/s↗13CAN XL
Higher-bandwidth CAN evolution
Automotive twisted pair and CAN XL-capable transceivers
Up to multi-megabit data phase depending on implementation↗14Camera and Display Links
High-speed video between cameras, displays and ECUs
Coaxial or shielded twisted-pair automotive video cable
Multi-gigabit serial data↗Isolation principle
DON’T UNPLUG AT RANDOM.
FOLLOW THE TOPOLOGY.
A controlled branch-by-branch isolation preserves evidence and prevents a second fault.