Siemens PLC LED Faults

My PLC and CANopen module displays the following LED’s:

Are there any suggestions for clearing these faults?

Hello HMS Support,

The PLC CANopen Module now gives me these flashing LED’s in the attached video. We had this working, but the CANBus dropped out. Do you have any suggestions?


Hello Bradly,

Based on the patter it seems like you are having errors on the CAN bus. Is your bus configured properly? What do you measure for voltage on the bus? Do you have terminating resistors at each end and are you measuring 60Ω?


CANBus is configured to be Transparent and 250 kpbs.

We don’t measure any voltage.

We have 120 ohm resistors on both ends and measure 60 ohms.

It’s worth noting that the PLC and IXXAT USB-to-CAN V2 are the only ones on the network.

Thanks for the update. I have asked my colleagues in Germany to take a look at this issue, I will update you tomorrow once I hear back.


Hi Bradley,

Here is the response that I received from my colleague.

It looks like you are running the CM CANopen in transparent CAN mode:
RUN LED is triple flash
ERR LED is Single flash:
Warning limit reached in CAN controller,
for example due to bad or no signal on the CANopen network.

Please check the following:

  • the mounting:
    see chapter 4.1 Mounting of the manual

  • is the CAN bus correctly terminated ?
    see chapter 4.4 Line Termination of the manual
    CAN bus has a line topology:

    • each end must be terminated with the specified resistor
    • exactly 2 resistors
  • the cable length
    see chapter4.3 Maximum Cable Lengths of the manual

  • runs every device with the correct CAN Baudrate ?

description of the LED patterns:
LED on
The LED shall be constantly on.
LED off
The LED shall be constantly off.
LED flickering
shall indicate the iso-phase on and off with a frequency of approximately 10 Hz:
on for approximately 50 ms and off for approximately 50 ms.
LED blinking
shall indicate the iso-phase on and off with a frequency of approximately 2,5 Hz:
on for approximately 200 ms followed by off for approximately 200 ms.
LED single flash
shall indicate one short flash (approximately 200 ms) followed by a long off phase (approximately 1000 ms).
LED double flash
shall indicate a sequence of two short flashes (approximately 200 ms),
separated by an off phase (approximately 200 ms).
The sequence is finished by a long off phase (approximately 1000 ms).
LED triple flash
shall indicate a sequence of three short flashes (approximately 200 ms),
separated by an off phase (approximately 200 ms).
The sequence is finished by a long off phase (approximately 1000 ms).
LED quadruple flash
shall indicate a sequence of four short flashes (approximately 200 ms),
separated by an off phase (approximately 200 ms).
The sequence is finished by a long off phase (approximately 1000 ms)

Also, are you using the library off of the Ixxat site? If you are we have an revised library. We would need to know what version of TIA you are using.


Thanks for your help, Deryck.

Currently we just have the PLC and the IXXAT USB-CANV2 on the network.

We had pin 3 referenced to chassis ground at one point and later changed it to 24VDC Common due to lesser noise. Our other two nodes were referenced to 24VDC Common. Would these two different references cause any damages to the CANBus’ hardware?

We have two 120 ohm resistors at each end.

Our total run is <3 meters long.

All are set to 250kpbs

I am using the library off IXXAT’s site for the HSP

I am using TIA V15


Hello Deryck,

Any word from Germany? We would like to remove the errors so we can read the CANBus message.


Hello @Bradley,

From what i understand of the issue currently it seems like the issue is most likely tied to an issue on the CAN bus or as you brought up in our last phone call it seems the CM module itself could be damaged.

The only way to test the module would be to see if the module sends any messages on the bus. To do this you would need a CAN tool and software (e.g.: MiniMon and USB-to-CAN) to test the bus with.

Do you have access to a USB-2-CAN?


Yes, we do have a USB-2-CAN Module, but we cannot see anything while running cananalyzer3mini. Does this indicate that we have a burned out PLC CANBus module?

This is what I am thinking I am waiting to hear back from my colleagues whether or not they agree.


We get the drives tonight and we have another HMS CANopen S7-1200 module if the one we have fails. I’ll keep you posted if the original module is busted.

Hello Bradley and Deryck,

I am currently configuring a system that is similair to that of Bradley, and i am experiencing the same flashing LEDs. I and am curious about how you managed to solve this? Do i understand correctly that
this signals a broken/defective module, and replacing this module did the trick?

Kind regards

Hi Mark,

This is where this particular issue ended, Bradley did not follow up further.

Do you have a USB to CAN to check for communications? You should see some communications on the bus.

If the device is setup for CANopen you should see bootup messages being sent.

If is configured for transparent CAN you will need to make sure the PLC is configured to send a message and if it is then you should see this on the bus.

If you suspect the device is damaged I recommend reaching out to your distributor to to fully diagnose the device and see if


Hi Deryck,

Thanks for your reply. I have followed up on troubleshooting with a USB to CAN-interface and found a mixup in the wiring. This if i remember correctly, eliminated the double red flash. A reboot after this eliminated the single red flash, after which the module was operating correctly.

Kind regards,

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Thanks for following up it is good to hear the issue was easily resolved and the device is not damaged.