Terminating Resistor

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

Fig 1: Identifying HS CAN (High Speed) Functional Block Diagram

Courtesy of VOLVO CARS OF NORTH AMERICA.

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

Fig 2: Identifying LS CAN (Low Speed) Functional Block Diagram

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 ohm

• For HS CAN (high speed), the terminating resistors are located in the brake control module (BCM) and the engine control module (ECM).
• For LS CAN (low speed), the terminating resistors are located in the upper electronic module (UEM) and the rear electronic module (REM).

Resistance measurement of parallel circuit with terminating resistor 

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

• When the CAN network is intact, the resistance on the network is approx. 60 ohm.
• In case of open circuits on the cables, so that 1 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.