CAN Troubleshooting Guide
Normally the voltage should be between 2.0 V and 4.0 V.
If it is lower than 2.0 V or higher than 4.0 V, it is possible that one or more nodes have faulty
transceivers. For a voltage lower than 2.0 V please check CAN_H and CAN_L conductors for
continuity. For a voltage higher than 4.0 V, please check for excessive voltage.
To find the node with a faulty transceiver please test the CAN transceiver resistance (see below).
7.5 CAN Transceiver Resistance Test
CAN transceivers have one circuit that controls CAN_H and another circuit that controls CAN_L.
Experience has shown that electrical damage to one or both of the circuits may increase the
leakage current in these circuits.
To measure the current leakage through the CAN circuits, please use an resistance measuring
device and:
1.
Switch off the node and disconnect it from the network
(see figure below).
2.
Measure the DC resistance between CAN_H and CAN_GND
(see figure below).
3.
Measure the DC resistance between CAN_L and CAN_GND
(see figure below).
The measured resistance has to be about 500 kΩ for each signal. If it is much lower, the CAN
transceiver it is probably faulty.
Another sign for a faulty transceiver is a very high deviation between the two measured input
resistance (>> 200%).
Figure. 10:
Measuring the internal resistance of CAN transceivers
CAN-USB/2
Hardware Manual • Doc. No.: C.2066.21 / Rev. 1.4
Page 23 of 25
4
5
6
CAN_H
CAN_GND
CAN_L
5
6
4
4
Power
CAN
transceiver
disconnect
power!
disconnect
CAN!
CAN node
