Problem Solving Questions

Why is my CAN not working ? Here are some Problem Solving Questions This page should help you to find out why your network is not working by providing questions. Answering these questions should help to find out what is possibly going wrong.

• Are there two 120 Ohm resistors across the bus at each end to terminate the network drivers? See CAN Cabling and DeviceNetCable

• Is there at least one other node on the bus?

• Are both CAN transceivers (when there are only 2 nodes) fault tolerant?

• Are all the nodes CAN-A or are there CAN-B compliant devices?

• Are the grounds between nodes connected together?

• Are you using a Commercial Off The Shelf (COTS) dongle to listen in on the messages. In other words: “can you trust at least one member at the bus?”.

• Are you using an CAN speed according your network cable length ? See CAN Cabling

If you can't detect the problem, segment the CAN bus into small parts to isolate the problem. Split the bus in the middle, then the side which caused the problem again, and again - this is the fastest way to find the cause.

For cabling problems this site shows some signal screen shots for common problems.

CANbus Academy has created a “CAN bus Troubleshooting - Quick Reference” which is available on request. This pdf contains some key test procedures to troubleshoot a CAN bus using a multimeter.