CAN Bus
Diagnostics & Protocols · 7 specs
Direct Answer
Controller Area Network (CAN Bus, invented by Robert Bosch GmbH in 1986 and standardized under ISO 11898) is the multi-master, message-broadcast serial bus governing electronic control units (ECUs). Operating at 500 kbps (High-Speed CAN) over a twisted pair with 120-ohm termination resistors, utilizing differential voltage signaling (CAN_H / CAN_L) and non-destructive bitwise arbitration.
Source: ISO 11898-1:2015 & ISO 11898-2:2016 / Bosch CAN Specification 2.0B · Last reviewed Aug 28, 2026
Specs
| Standardization | ISO 11898-2 (High-Speed physical medium) / SAE J2284 |
| Transmission Speed | 500 kbps standard for powertrain (Engine, Transmission, ABS, Airbag); 125-250 kbps for body electronics |
| Differential Voltage Levels | Recessive state (Logic 1): CAN_H = 2.5V, CAN_L = 2.5V (Diff = 0V) | Dominant state (Logic 0): CAN_H = 3.5V, CAN_L = 1.5V (Diff = 2.0V) |
| Bus Termination | Exactly two 120 Ω terminating resistors at opposite physical ends of the bus (total measured resistance between CAN_H & CAN_L = 60.0 Ω) |
| Frame Format (CAN 2.0B) | 11-bit standard identifier or 29-bit extended identifier with up to 8 data payload bytes |
| Bitwise Arbitration | Dominant zero bits overwrite recessive one bits; the lowest numerical CAN ID has the highest priority and never loses arbitration |
| Fault Confinement | Hardware error counters automatically transition faulty nodes from Error-Active -> Error-Passive -> Bus-Off isolation |
Differential Noise Cancellation Physics
Automobiles are harsh electromagnetic environments with ignition coils and alternator field switching generating hundreds of volts of RF noise. Because CAN signals travel over twisted pair wires, any external EM spike induces an identical voltage bump in both wires simultaneously. Because the receiver measures only the differential voltage (V_diff = CAN_H–CAN_L), the common-mode noise is completely subtracted to zero.