[Ovmsdev] UDS write by identifier help

[Shane @ Kilve Engineering]

Hi Michael, 

I have now switched to obdii requests

Have now worked out the commands need to be sent quickly 

I now get 
OVMS# obdii can1 request device 735 7b5 1003
735[7b5] 1003: Response:
00 32 01 f4                                     | .2..            
I (57401468) webserver: HTTP POST /api/execute
I (57401478) webcommand: HttpCommandStream[0x3f8b52a0]: 3499452 bytes free, executing: obdii can1 request device 735 7b5 2ee01040ea85ce
OVMS# obdii can1 request device 735 7b5 2ee01040ea85ce
735[7b5] 2ee01040ea85ce: ERROR: request failed with response error code 33 securityAccessDenied

So obviously do need security so have now done a 
OVMS# obdii can1 request device 735 7b5 1003
735[7b5] 1003: Response:
00 32 01 f4                                     | .2..            
I (64032248) webserver: HTTP POST /api/execute
I (64032258) webcommand: HttpCommandStream[0x3f8b5268]: 3499932 bytes free, executing: obdii can1 request device 735 7b5 2701
OVMS# obdii can1 request device 735 7b5 2701
735[7b5] 2701: Response:
3a 07 4e 87                                     | :.N.            

And get a seed back :-)

But without access to a services device I guess its going to be hard to work out the encryption !

Regards
Shane 
> On 25 Oct 2021, at 12:46, Michael Balzer <dexter at expeedo.de> wrote:
> 
> 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
>> _______________________________________________
>> OvmsDev mailing list
>> OvmsDev at lists.openvehicles.com
>> http://lists.openvehicles.com/mailman/listinfo/ovmsdev
> 
> -- 
> Michael Balzer * Helkenberger Weg 9 * D-58256 Ennepetal
> Fon 02333 / 833 5735 * Handy 0176 / 206 989 26
> 
> 
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