CAN 2 interrupted when plugging in C127 Dash

[Jolly Wrenchers]

This ECU/Dash combination was purchased through a firmware developer here in the US, I noticed in the help file the AU based support so did try reaching out there, but they are sending me back to the dealer I purchased from.

I’m certain I will hear from them as time allows, the hope was I could speed things along using any available resources such as this forum.

My biggest concern is just trying to be certain I haven’t introduced a problem with my settings, if not what wiring issue may be present, or is there a behind the scene’s firmware type issue. If I can figure that out I can determine how to best prioritize my time.

FWIW I did confirm yesterday that the “Race Loom” does in fact have the 100 ohm resistor installed in it. Also, while it was configured to try communications over CAN1 when I grabbed the files to send you, I have also tried over CAN2. Further investigation shows the dash is currently physically only connected to CAN2 so I won’t be wasting anymore time looking at CAN1 configurations.

I do wish I better understood better what to look for in the LTCD/Dash relationship to make sure I don’t have an address competing between the two or something like that. Another test I will try (retry?) is to physically remove the LTCD from the wiring and see if I can get ECU/Dash comms working. If so that should confirm some type of data conflict between the LTCD and the C127.

[David Ferguson]

It's pretty clear, that if you configure it as Stephen is suggesting it should work. it is a combinations of settings, and maybe the wiring -- but you don't seem to be following up on the suggestions.

[Stephen Dean]

Picture a freeway in peak hour with cars travelling along at 50kph, this is CAN Bus 1, as it is currently configured, between the M1 and the Dash. When you plug the LTC into this bus, it is the same as introducing a car travelling at 100kph onto the freeway. As you could imagine, carnage ensues and the freeway stops moving, same as the CAN Bus does when a device at a difference Bus rate is connected.

The way that the wiring needs to be configured to work correctly is as follows.

M1 CAN Bus 1 (500k) <-> C127 CAN Bus 1 (500k)
M1 CAN Bus 2 (1m) <-> LTCD (1m)

You do not need to connect the LTCD to the C127, the M1 will retransmit the relevant data from the LTCD to the C127 over the CAN Bus, as long as the ECU Transmit is set to CAN Bus 1.

The attached file reflects this.

[Jolly Wrenchers]

Thank-you for the clarification on the M1 CAN 1 being able transmit data coming in on CAN 1 and CAN 2. This brings even more focus so I’m not chasing as many variables. Would this also be true of CAN 2, the M1 receiving all of the CAN 1 and CAN 2 data, then transmitting it to the dash over CAN 2?

If M1 CAN 1 is working receiving at 500Khz, CAN 2 is working to receive the LTCD (and eventually other MoTeC products) over CAN 2 1Mhz, M1 transmit set to CAN 2, dash configured to receive CAN 2 this should all play well together correct? This is a scenario I have tried many times now. This configuration works until the dash is plugged in and powered up. I can see the CAN data for CAN 1 and CAN 2 in results in M1 tune and in the MoTeC CAN viewer software all functioning as expected. Regardless of dash configuration, such as set to receive on CAN 2 or even no configuration parameters loaded, it brings down CAN 2 as soon as it the dash is connected and powered up.

I am being quite careful to make sure whatever the CAN setup is in the M1 transmit is matched in the Dash configuration. If/when that doesn’t work I do try other scenario’s.

In my dash race loom, only CAN 2 is wired through (green and white wires). In testing the wiring I found that there is a 100 ohm terminating resistor in that race loom, and I am not finding another resistor in any of the other CAN 2 wiring. I added a 100ohm resistor at the LTCD module connection to see if that would help as suggested by the developer, we noticed no change.

Stephen, if you feel it makes sense, I can run a CAN 1 pair to the Dash and see if things will work on that CAN that aren’t working on CAN 2.

David, I am certainly doing my best to follow any and all suggestions, if you are able to point to something I am missing please do, it certainly isn’t intentional.

[Stephen Dean]

I have reconfigured the attached file so that the configuration will now match your wiring. M1 ECU Transmit should be set to CAN Bus 1 as this is the Bus that is wired to the C127 and also has the OEM CAN Data on it.

M1 CAN Bus 1 (500k) <-> C127 CAN Bus 2 (500k) <-> OEM CAN Bus (500k)
M1 CAN Bus 2 (1M) <-> LTCD (1M)

When you where plugging the dash in before, as CAN Bus 2 on the dash was configured to run at 1M, this was causing the Bus to crash.

Who was the dealer that sold the hardware to you?

[Jolly Wrenchers]

As mentioned above the only CAN wiring going to the dash is CAN 2, not CAN 1. CAN 1 would get to the dash through a 6 way connector from the CAN expansion harness, the CAN expansion harness that came with the kit didn't terminate in one of these, only the 4 pin connector, labeled DASH.

I took the time to go wire by wire testing CAN from the Dash to the ECU. I found a discrepancy in the 4 pin connector from the dash harness to the CAN expansion harness. At that connector, the white CAN 2 wire from the ECU was not pinned to the same terminal as the white CAN 2 wire going to the designated pin on the dash.

With that corrected so that CAN 2 both high and low are now getting to the designated pins from ECU to dash, I am no longer losing CAN 2 when I plug in and power up the dash.

[Stephen Dean]

Was that a MoTeC supplied loom?

[Jolly Wrenchers]

I have to believe so. I’m trying to get a pin out or schematic of the loom so that I can verify the rest of the terminations.

[Stephen Dean]

This is the link to the loom that comes with the Race kit for the C12x Displays. 62204

[Jolly Wrenchers]

Edited to note answered my own question on blue and pink wires, used for RS232 communications so not relevant to my project.

This is the link to the loom that comes with the Race kit for the C12x Displays. 62204

Thank-you Stephen, this and the pin out of the M150 in the wiring help is how I determined something was amiss on the the CAN 2 wiring.

From the main M150 loom, the 4 pin CAN 2 related connector (picture attached) has the wires for CAN in positions 2 (green) and 3 (white), and the Race Loom has them in pin positions 3 (green) and 4 (white). Originally I tried changing the wire positions at the beginning of the CAN expansion cable, but of course then the LTCD and the CAN itself went down. This made sense as the rest of the MoTeC CAN modules would be expecting the original pin assignment. Where I am confused is why does the dash want the 4 pin wire assignment different than the other modules? I was anticipating all 4 wire CAN connectors for each CAN device on a shared CANbus to have CAN High and CAN Low in the same pin location throughout.

What I could use help with is the other 2 wires (blue and pink) in the C12X 4 pin connector, what dash inputs should be on those wires? I am asking because while the CAN no longer drops when the dash is plugged in and powered up, I am still not seeing any CAN activity displayed in the dash. My hope is that it is related to those 2 wires.