Volvo Trucks - SAE 1939 and 2284

The two outer resisters represent the circuit Terminating resisters, that can be wired into the harness or inside a control unit. The three other resisters represent other control units. The SAE 2284 CAN Controlled Area Network, runs at 500 kbs (Kilo bits per second). The SAE 1939 CAN runs at 250 kbs. The CAN high line runs at around 2.7v and the CAN Low line runs at 2.4v. The same message is on both lines. To terminate the signals and help prevent interference you twist the wires and fit 2 termination resisters at the ends of the line. They are 120 ohms. In parallel that makes 60 ohm. The internal resistance of the other 3 ECU on this circuit is around 35Kohm. Switch on the Ohm meter to view the circuit resistance. Switch on the power switch to view CAN voltage.

published 4 years ago