Terminating Resistor

High-speed net HS CAN (High Speed), example 

Fig 1: Identifying Terminating Resistor High-Speed Net HS CAN (High Speed)

Courtesy of VOLVO CARS OF NORTH AMERICA.

Low-speed net LS CAN (Low Speed), example 

Fig 2: Identifying Terminating Resistor Low-Speed LS CAN (Low Speed)

Courtesy of VOLVO CARS OF NORTH AMERICA.

To prevent electrical reflections and interference in the CAN network, there are terminating resistors which bridge CAN H (High) and CAN L (Low), one at each end (main line) on both the high and low speed sides of the network. Each terminating resistor has a resistance of 120 Ω.

• For the HS CAN (High Speed) the terminating resistor is in the steering wheel module (SWM) and the engine control module (ECM)
• For the LS CAN (Low Speed) the terminating resistors are in the driver information module (DIM) and the supplemental restraint system module (SRS).

Resistance measurement of parallel circuit with terminating resistor 

Both the terminating resistors create a parallel circuit. The following resistances can be measured under specified conditions:

• When the control area network (CAN) is intact the resistance on each side of the network is approximately 60 Ω.
• In case of open circuits on the cables, so that a terminating resistor is not included in the circuit, the resistance in the net is approx. 120 ohm (only one main line is measured).
• An open circuit on the cables to control modules located "outside" the measured circuit cannot be detected with this measurement.
• In case of short-circuiting between the communication cables, the resistance is approx. 0 ohm between the cables, regardless of where the short-circuiting is located.