Hi,

I'm trying to create a small logger for an older Siemens ECU.

Normally I try to find pattern in the response value and create the formula. Normally this working quite good, but I'm stuck at the moment with some temperature values that are a 3 byte answer.
Maybe someone is aware of a typical pattern how Siemens outputs float values on obd with 3 bytes.

byte 2 and 3 looking pretty clear to me, they are (with a factor) multiplied. but I can't find the pattern on the first byte.

Any ideas?

value	byte1	byte2	byte3
13,5	0x05	0x87	0x65
2727,0	0x01	0x87	0x65
27,3	0x02	0x87	0x65
27,3	0x03	0x87	0x65
-35,1	0x04	0x87	0x65
13,5	0x05	0x87	0x65
13,6	0x06	0x87	0x65
0,0	0x0a	0x87	0x65
0,6	0x0b	0x87	0x65
13,6	0x0c	0x87	0x65
-3,5	0x0d	0x87	0x65
0,0	0x10	0x87	0x65
0,0	0x11	0x87	0x65
5454,0	0x12	0x87	0x65
0,0	0xa0	0x87	0x65
0,0	0xa1	0x87	0x65
6108.5	0xa2	0x87	0x65
2700,0	0x01	0x87	0x65
2727,0	0x01	0x87	0x66
2754,0	0x01	0x87	0x67
2781,0	0x01	0x87	0x68
2808,0	0x01	0x87	0x69
2660,0	0x01	0x85	0x64
2680,0	0x01	0x86	0x64
2700,0	0x01	0x87	0x64
2720,0	0x01	0x88	0x64
2740,0	0x01	0x89	0x64
2760,0	0x01	0x90	0x64
2686,6	0x01	0x85	0x65
2706,8	0x01	0x86	0x65
2727,0	0x01	0x87	0x65
2747,2	0x01	0x88	0x65
2767,4	0x01	0x89	0x65
2787,6	0x01	0x90	0x65

It looks like kwp2000,. I have tested various values and byte combinations with original ecu and also with an emulated ecu to inject every Byte combination that I want. But this values is really strange, I just can't figure it out what the first byte does.