OVMS issue: obdii on can3 crashes VMS

[pd_australia]

Your cable connects/ exposes can3 from the extension port (the 26 pin connector) to the OBD2 connector. The issue is, as @gregd points out, that can3 is also connected on the other side, from the 9pin connector on the OVMS to the car. So you will need to disconnect can3 on the car side of the OVMS so that the HUD communication doesn't reach the car.

I am attaching the relevant pin connection diagram for the 9 pin connector (from the OVMS v3 Developer Guide, see also post #9 from @markwj above) Note that the numbering starts with 0 in this chart, while the OVMS commands start with one, so can3 will be labeled "can2" in these charts.

So you will need to grab the cable that connects the OVMS to the Roadster and either cut the wires on pins 6 and 8 on the 9-pin connector, or remove/cut pins 2 and 7 on the roadster-end of the cable (the big rectangular connector).

I ended up rewiring the cable from the OVMS to the HUD to use can2 so that can3 would be available for future ESS related functionality in OVMS - therefor I had to disconnect the pins labeled "can1" in the charts.

Let me know if you need a photo of the cable - I can pull it out and grab a photo if helpful.

Thanks @Peter.h. I think i'd prefer to do the same and rewire the cable from OVSM to HUD, rather than missing with the other side .

Could I rewire the DA26 Connector and maybe get a male and female, and rewire CAN3 to CAN2? (In diagram below probably CAN2 to CAN1) and not connect the other two CAN busses?

OVMS Diag Port < ==== > DA26 Connector Male+Female (Rewiring CAN3 to CAN2 and disabling others) < ==== > OVMSv3 HUD to OBDII cable < === > HUD

 

[gregd]

I think i'd prefer to do the same and rewire the cable from OVSM to HUD, rather than missing with the other side .

The OBD2ECU function can use either CAN3 or CAN3, but the key is to not send its traffic to the car. So, regardless of which CAN bus you use, modification to the OVMS to Roadster cable is needed. Using CAN2 instead of CAN3 seems to not interfere with the car's operation (they're both at the same bit rate), but you're still sending OBDII traffic into a car that's not designed for those messages, nor the extra traffic load on the bus. No telling what the side effects might be under all conditions, so I strongly recommend against it.

If you are needing to use the new CAN3-based functions (e.g. TPMS), then using CAN2 on the 26 pin OBDII connector AND disconnecting CAN2 from the car would be the right solution. Given that the OBDII cable is molded on both ends, this isn't trivial. Otherwise, just pull or clip the two CAN3 pins from the Roadster end of the OVMS cable, and you're good.

 

[Peter.h]

That should work. What I did was get a new male DA26 connector and shell and replaced the molded end of the OBD2 cable. I can look up the past numbers if needed. That's a bit easier and saves having too many connections.

 

[gregd]

My strong recommendation is to ALWAYS remove whichever CAN bus being used for the HUD from the car-end of the OVMS. Not optional. Then it's your choice on whether to leave the 26 pin cable as manufactured and use CAN3, or modify it and use CAN2. Modifying both cables so you can use CAN2 allows the use of CAN3 for the TMPS function. Modifying only the OVMS-to-Car cable sacrifices TPMS for not having to modify the other cable. Modifying only the 26 pin cable is not an option I would recommend.

 

[Peter.h]

My strong recommendation is to ALWAYS remove whichever CAN bus being used for the HUD from the car-end of the OVMS. Not optional.

to clarify - I fully agree and I modified both cables. I was just responding to the question how to handle the “downstream” part of modification.

for the roadster-to-OVMS called my strong preference is to depin the car end of the cable (the rectangular connector). It’s relatively simple to hold down the retainer on the pin with a micro screwdriver and pull the pins out, then wrap them in electrical tape for future use.