CAN Bus
Controller Area Network — the internal communication system inside modern vehicles that allows electronic control units (ECUs) to share data, enabling telematics devices to read engine data, fault codes, fuel consumption, and driver inputs.
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Compare Telematics software →How CAN Bus Works Inside a Vehicle
The Controller Area Network was developed by Bosch in the 1980s and became the dominant vehicle communication standard through the 1990s. Before CAN, each sensor in a vehicle needed its own dedicated wire to every control unit that needed its data — a wiring complexity nightmare as vehicles added more electronics. CAN replaces point-to-point wiring with a two-wire differential bus (CAN High and CAN Low) that all ECUs connect to. Each ECU broadcasts messages containing an identifier and data payload. Every other ECU on the bus receives every message and decides whether to act on it based on the identifier. This means the engine ECU can broadcast coolant temperature once, and the instrument cluster, the telematics module, and the transmission controller all receive it simultaneously.
What Telematics Devices Read from CAN Bus
A telematics device connected to a vehicle's CAN bus acts as a passive listener — it receives broadcast messages from every ECU on the network without actively interfering with vehicle operation. From the powertrain CAN, a quality device reads engine RPM, vehicle speed, accelerator pedal position, throttle position, fuel rate, intake air temperature, coolant temperature, and engine load percentage. From the body control CAN, it can read seatbelt status, door open/close events, and auxiliary switch activations. From the ABS/brake controller, it reads brake pedal activation events. This breadth of data enables telematics platforms to build rich driver behavior profiles without any sensor beyond the CAN connection.
Proprietary Extensions: Why Not All Data Is Available
The J1939 and OBD-II standards define a core set of Parameter IDs (PIDs) and Parameter Group Numbers (PGNs) that manufacturers must support. But automakers and truck OEMs routinely add proprietary messages on the same CAN bus using manufacturer-specific identifiers. Fuel level, seatbelt status, door open events, and odometer are often in proprietary locations. This is why two vehicles from different manufacturers running the same telematics device may expose different data — the standardized PIDs are consistent, but proprietary extensions vary. Telematics vendors maintain libraries of vehicle-specific CAN message decodings (vehicle profiles) that expand available data. A large vendor may have profiles for 2,000+ vehicle configurations; a smaller vendor might support 200.
Real-World Example: CAN Bus Enabling Preventive Maintenance
A regional concrete ready-mix company operated 31 concrete mixer trucks with engine hours running 2,000–3,500 hours annually — significantly more than a typical vehicle's annual mileage would suggest for maintenance scheduling. Their telematics system read engine hours directly from the J1939 CAN bus and automatically triggered service work orders in their maintenance software when each truck hit 250-hour intervals for oil changes and 500-hour intervals for filter service. Before CAN-integrated telematics, maintenance was scheduled by calendar and frequently missed because a drum mixer might run 400 engine hours in 45 calendar days during a busy concrete pour season. After implementation, engine-hours-based scheduling reduced unplanned breakdowns by 34% in the first year.
- Confirm the telematics device reads CAN bus data, not just GPS — look for RPM, fuel rate, and engine hours in the feature list
- Ask the vendor how many vehicle profiles they support for proprietary CAN decoding
- Verify the device does not actively transmit on the CAN bus — passive reading only is the safe standard
- Check whether OBD-II and J1939 are handled by the same device or require different hardware for mixed fleets
- Confirm CAN data update frequency — 1-second updates enable accurate idle detection; 10-second updates miss short stops
- Ask whether the platform exposes raw CAN data via API for integration with maintenance systems