MC3 CAN, no contact and CAN error (bus off)

The No contact error is triggered when there is a timeout for any of the CAN modules connected to the IQAN master.
You could for example get this error if you switch of power to one of the modules, or if the CAN wires are cut.
The IQAN master will be able to recover from this fault during operation, if it was just a timeout, the communication will resume when the module starts responding on the CAN bus again.

CAN critical means that the IQAN-MC3 CAN controller has gone into bus-off. When the IQAN-MC3 has gone into bus-off, this CAN bus will stay switched of until the IQAN-MC3 is switched off and back on again.
The CAN critical comes from faults on a lower level, it is a consequence of too many incorrect CAN frames on the bus in a short time.
Physical problems like shorting of CAN wires would cause this, for such errors the effect would be almost instant (when there is traffic on the bus)
Lack of proper termination could cause this.
Too long drop-lines could cause this.
Setting the wrong baudrate on one of the nodes would case this, also this case would be almost instant.
If two nodes send out messages with the same ID on the bus, then you could have this.
If you connected your IQAN module to another module with incorrect bit-timing this error could be the result, but that would be a severe design flaw on that module, I would not expect that in the field.
Significant voltage potential differences between CAN nodes could cause this, if there is bad grounding between the modules and large loads switching on and off that could case intermittent problems like this. From expericence, this is the one thing I would recommend focusing on if you see a mix of both CAN critical errors and No contact errors in the log.

It can be quite tricky to know the root cause just from the error message, as almost all the problems that could give CAN critical may also cause the No contact error. If one module in the system switches off with a CAN critical error code, the other nodes expecting information from this node will get a No contact with that module.