[Ovmsdev] UDS write by identifier help

[Michael Balzer]

Shane,

not sure why you don't use the OBD request command for this instead of 
manual frame assembly.

However, regarding writes to PIDs:

- You may need another session type. Most cars now won't accept 03 as a 
session with PID write access, but expect some custom session type to 
allow that. The NRC 7F means "serviceNotSupportedInActiveSession" (btw: 
the OBD command translates the most common NRCs for you), which is a 
hint you need another session.

- You normally don't need tester presence if you send the request 
shortly after the session init. Most devices will keep a session logged 
in for at least 60 seconds, custom session types may expire faster. Use 
a script if in doubt, or start a tester presence signal using the "re 
obd tester" subcommand.

- I doubt you do, but if (!) you really need security access (request 
27), that will normally work differently. See section 9.4 in the ISO 
document: you need to create a key from the seed given by the server. So 
you need to know how to calculate the key, which normally involves some 
non-obvious encryption method. You may be able to derive the method from 
looking at CAN logs of a service device gaining access.

I would try other session types first.

Hint: you can use a script to walk through a range of session types and 
try the write after each one.

See: 
https://docs.openvehicles.com/en/latest/userguide/scripting.html#ovmsvehicle 
→ OvmsVehicle.ObdRequest(arguments)

Be aware that's a synchronous call, so don't let the loop run for longer 
than 60 seconds to avoid the watchdog.

Regards,
Michael


Am 25.10.21 um 11:06 schrieb Shane @ Kilve Engineering:
> Hi all,
>
> Can anyone give me some help trying to write data to the TPMS ecu?
>
> I can read for example FL tyre using
> can can1 tx standard 735 03 22 e0 10 00 00 00 00 (FL id e010 FR e020 etc.)
> And get back 07 62 e0 10 80 2d b9 d4
>
> I have confirmed that the tyre id is "80 2d b9 d4” with a tmps reader wireless at the wheel
>
> I have then done a session control with
> can can1 tx standard 735 02 10 03 00 00 00 00 00
> And get back 06 50 03 00 32 01 f4 00
> So that looks ok ?
>
> So I then try
> can can1 tx standard 735 07 2e e0 10 40 ea 85 ce (the new id)
> And get back 03 7f 2e 7f
>
> So ive tried issuing
> can can1 tx standard 735 02 27 01 00 00 00 00 00
>
> But get no response??
>
>
> any pointers?
> p.s. do I also need to be sending tester present to the ecu? Or does the fact im doing a session control take care of this?
>
>
> Regards
> Shane
> _______________________________________________
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> OvmsDev at lists.openvehicles.com
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-- 
Michael Balzer * Helkenberger Weg 9 * D-58256 Ennepetal
Fon 02333 / 833 5735 * Handy 0176 / 206 989 26


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