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I'm trying to reverse engineer data received from TPMS (car tire pressure) sensors. I was able to receive and demodulate the data (433 MHz, FSK, Manchester encoding).

Probable packet fields:

bytes 1-4: sensor id (4 distinct values detected)

bytes 5-9: unknown (temp/pressure)

byte 10: 8-bit CRC detected by using reveng

In the 5 unknown bytes there should be encoded tire pressure and tire temperature and some status bits. However I was not able to guess how are these temp/pressure data encoded. The pressures as shown by car were in the range 211-220 kPa, temperature between 5-15 degrees.

Can you help me decoding the temperature and pressure from the below data or at least point me to some direction?

Here is the detected data from sensors:

 sensor_id        temp/press       CRC

1f e0 ed a5     42 d5 66 c7 f1     10
1f e0 ed a5     42 d4 66 c7 f1     06
1f e0 ed a5     44 d6 66 c7 e4     0a
1f e0 ed a5     44 d4 66 c7 e4     26
1f e0 ed a5     55 d4 68 c8 da     23
1e e0 ed a5     42 d5 66 c7 db     bf
1e e0 ed a5     41 d6 65 c8 cb     2d
1e e0 ed a5     41 d5 65 c8 cb     17
1e e0 ed a5     55 d5 68 c8 f7     8f
1e e0 ed a5     55 d4 68 c8 f7     99
1d e0 ed a5     44 d6 66 c7 f7     81
1d e0 ed a5     41 d5 64 c8 eb     17
1d e0 ed a5     55 d5 68 c8 da     c7
1d e0 ed a5     42 d5 65 c7 c8     f0
1d e0 ed a5     42 d4 65 c7 c8     e6
1c e0 ed a5     44 d5 65 c8 d9     76
1c e0 ed a5     41 d4 64 c8 d3     d0
1c e0 ed a5     55 d6 67 c8 df     d8
1c e0 ed a5     55 d5 67 c8 df     e2
1c e0 ed a5     55 d4 67 c8 df     f4
1c e0 ed a5     42 d6 65 c7 ef     46
1c e0 ed a5     42 d5 65 c7 ef     7c
1c e0 ed a5     42 d4 65 c7 ef     6a
1f e0 ed a5     44 d6 65 c7 f3     d2
1f e0 ed a5     44 d4 65 c7 f3     fe
1f e0 ed a5     41 d5 64 c8 f6     b6
1f e0 ed a5     41 d4 64 c8 f6     a0
1f e0 ed a5     42 d6 65 c7 f9     af
1f e0 ed a5     42 d4 65 c7 f9     83
1e e0 ed a5     42 d6 64 c7 f7     97
1e e0 ed a5     42 d5 64 c7 f7     ad
1e e0 ed a5     42 d4 64 c7 f7     bb
1f e0 ed a5     55 d6 67 c8 f5     85
1f e0 ed a5     55 d5 67 c8 f5     bf
1d e0 ed a5     42 d5 64 c7 f3     3a
1d e0 ed a5     42 d4 64 c7 f3     2c
1e e0 ed a5     44 d6 64 c7 f4     d5
1e e0 ed a5     44 d5 64 c7 f4     ef
1e e0 ed a5     44 d4 64 c7 f4     f9
1e e0 ed a5     41 d4 64 c8 f6     d9
1e e0 ed a5     55 d6 67 c8 f7     f2
1c e0 ed a5     42 d5 64 c7 f3     43
1d e0 ed a5     44 d6 64 c7 f4     5e
1d e0 ed a5     44 d5 64 c7 f4     64
1d e0 ed a5     55 d6 68 c8 f5     30
1d e0 ed a5     55 d5 68 c8 f5     0a
1d e0 ed a5     55 d4 68 c8 f5     1c
1f e0 ed a5     42 d5 65 c7 f4     b6
1c e0 ed a5     44 d6 65 c7 f5     4b
1c e0 ed a5     44 d4 65 c7 f5     67
1c e0 ed a5     41 d6 64 c8 f2     1b
1c e0 ed a5     41 d5 64 c8 f2     21
1c e0 ed a5     41 d4 64 c8 f2     37
1c e0 ed a5     55 d6 67 c8 ed     46
1c e0 ed a5     55 d5 67 c8 ed     7c
1e e0 ed a5     42 d5 64 c7 f3     b1
1e e0 ed a5     42 d4 64 c7 f3     a7
1f e0 ed a5     44 d6 64 c7 f3     b9
1f e0 ed a5     44 d5 64 c7 f3     83
1f e0 ed a5     44 d4 64 c7 f3     95
1f e0 ed a5     41 d5 64 c8 ed     f7
1f e0 ed a5     41 d4 64 c8 ed     e1
1f e0 ed a5     55 d4 67 c8 ea     f4
1d e0 ed a5     42 d6 64 c7 dc     cd
1d e0 ed a5     42 d4 64 c7 dc     e1
1e e0 ed a5     44 d6 64 c7 da     1f
1e e0 ed a5     44 d5 64 c7 da     25
1e e0 ed a5     44 d4 64 c7 da     33
1e e0 ed a5     41 d4 64 c7 f4     14
1e e0 ed a5     55 d6 67 c8 f2     e9
1e e0 ed a5     55 d5 67 c8 f2     d3
1c e0 ed a5     42 d6 63 c7 c3     ff
1c e0 ed a5     42 d5 63 c7 c3     c5
1c e0 ed a5     42 d4 63 c7 c3     d3
1d e0 ed a5     41 d6 63 c7 dd     7a
1d e0 ed a5     41 d4 63 c7 dd     56
1d e0 ed a5     55 d6 67 c8 e0     1c
1d e0 ed a5     55 d5 67 c8 e0     26
1f e0 ed a5     42 d6 64 c6 d6     1c
1c e0 ed a5     44 d6 63 c7 d9     f2
1c e0 ed a5     44 d4 63 c7 d9     de
1c e0 ed a5     41 d6 63 c8 d4     ff
1c e0 ed a5     41 d5 63 c8 d4     c5
1c e0 ed a5     55 d4 67 c8 d6     cb
1f e0 ed a5     44 d6 64 c7 d3     59
1e e0 ed a5     42 d5 64 c6 d4     51
1f e0 ed a5     41 d6 63 c7 e9     04
1f e0 ed a5     41 d4 63 c7 e9     28
1f e0 ed a5     55 d6 67 c8 eb     df
1f e0 ed a5     55 d4 67 c8 eb     f3
1e e0 ed a5     44 d6 63 c7 9d     db
1e e0 ed a5     44 d5 63 c7 9d     e1
1d e0 ed a5     42 d4 63 c6 9a     37
1e e0 ed a5     41 d6 63 c7 d6     c0
1e e0 ed a5     41 d5 63 c7 d6     fa
1e e0 ed a5     55 d6 66 c8 cf     31
1e e0 ed a5     55 d5 66 c8 cf     0b
1d e0 ed a5     44 d6 62 c7 f4     23
1d e0 ed a5     44 d5 62 c7 f4     19
1c e0 ed a5     42 d6 63 c6 f5     68
1c e0 ed a5     42 d5 63 c6 f5     52
1c e0 ed a5     42 d4 63 c6 f5     44
1d e0 ed a5     41 d6 63 c7 df     74
1c e0 ed a5     55 d4 66 c8 f7     47
1c e0 ed a5     41 d5 63 c7 f5     e1
1c e0 ed a5     44 d6 64 c6 e4     42
1f e0 ed a5     42 d6 5f c6 d4     1f
1f e0 ed a5     42 d5 5f c6 d4     25
1f e0 ed a5     42 d4 5f c6 d4     33
1f e0 ed a5     55 d6 67 c8 eb     df
1f e0 ed a5     41 d6 61 c7 dd     5e
1f e0 ed a5     41 d5 61 c7 dd     64
1f e0 ed a5     41 d4 61 c7 dd     72
1e e0 ed a5     42 d4 62 c6 f2     c8
1e e0 ed a5     55 d6 66 c8 e4     e0
1e e0 ed a5     55 d5 66 c8 e4     da
1e e0 ed a5     55 d4 66 c8 e4     cc
1e e0 ed a5     41 d4 62 c7 e2     0b
1e e0 ed a5     44 d6 63 c6 f5     d1
1e e0 ed a5     44 d4 63 c6 f5     fd
1d e0 ed a5     42 d6 60 c6 e4     db
1d e0 ed a5     42 d5 60 c6 e4     e1
1d e0 ed a5     42 d4 60 c6 e4     f7
1d e0 ed a5     41 d6 62 c6 f4     db
1d e0 ed a5     41 d5 62 c6 f4     e1
1d e0 ed a5     41 d4 62 c6 f4     f7
1d e0 ed a5     44 d5 63 c6 f3     72
1d e0 ed a5     44 d4 63 c6 f3     64
1c e0 ed a5     42 d6 61 c5 ef     c7
1c e0 ed a5     44 d5 62 c6 c6     eb
1f e0 ed a5     42 d5 61 c5 dd     e8
1f e0 ed a5     42 d4 61 c5 dd     fe
1f e0 ed a5     41 d6 62 c7 f1     27
1f e0 ed a5     41 d5 62 c7 f1     1d
1f e0 ed a5     41 d4 62 c7 f1     0b
1f e0 ed a5     44 d6 62 c5 d6     15
1f e0 ed a5     44 d4 62 c5 d6     39
1e e0 ed a5     42 d5 61 c5 9f     58
1e e0 ed a5     42 d4 61 c5 9f     4e
1c e0 ed a5     55 d5 65 c7 85     76
1e e0 ed a5     41 d6 62 c6 ca     ea
1e e0 ed a5     41 d4 62 c6 ca     c6
1e e0 ed a5     44 d5 61 c6 f3     2f
1d e0 ed a5     42 d6 60 c5 f0     88
1d e0 ed a5     42 d5 60 c5 f0     b2
1d e0 ed a5     42 d4 60 c5 f0     a4
1f e0 ed a5     55 d5 65 c7 e8     f9
1d e0 ed a5     41 d6 61 c6 ec     2e
1d e0 ed a5     41 d5 61 c6 ec     14
1d e0 ed a5     41 d4 61 c6 ec     02
1d e0 ed a5     44 d5 62 c5 ea     69
1d e0 ed a5     44 d4 62 c5 ea     7f
1c e0 ed a5     42 d6 5c c4 ea     b9
1c e0 ed a5     42 d4 5c c4 ea     95
1e e0 ed a5     55 d5 65 c7 e2     b6
1c e0 ed a5     41 d6 61 c6 e4     6f
1c e0 ed a5     41 d4 61 c6 e4     43
1c e0 ed a5     44 d6 61 c5 e6     b3
1c e0 ed a5     44 d5 61 c5 e6     89
1c e0 ed a5     44 d4 61 c5 e6     9f
1f e0 ed a5     42 d6 61 c4 dd     c7
1f e0 ed a5     42 d4 61 c4 dd     eb
1d e0 ed a5     55 d5 65 c7 d3     aa
1d e0 ed a5     55 d4 65 c7 d3     bc
1f e0 ed a5     41 d6 61 c6 da     5e
1f e0 ed a5     41 d5 61 c6 da     64
1f e0 ed a5     44 d5 61 c5 ec     34
1e e0 ed a5     42 d6 60 c4 e9     59
1e e0 ed a5     42 d4 60 c4 e9     75
1e e0 ed a5     41 d6 62 c6 d6     be
1e e0 ed a5     41 d5 62 c6 d6     84
1e e0 ed a5     44 d6 61 c5 d9     fc
1e e0 ed a5     44 d4 61 c5 d9     d0
1d e0 ed a5     42 d6 60 c3 de     3c
1d e0 ed a5     42 d5 60 c3 de     06
1d e0 ed a5     42 d4 60 c3 de     10
1d e0 ed a5     41 d6 61 c6 e2     04
1d e0 ed a5     44 d5 61 c5 df     5f
1d e0 ed a5     44 d4 61 c5 df     49
1c e0 ed a5     42 d6 5f c4 d8     9a
1c e0 ed a5     42 d5 5f c4 d8     a0
1c e0 ed a5     42 d4 5f c4 d8     b6
1f e0 ed a5     55 d6 65 c7 d8     53
1f e0 ed a5     55 d4 65 c7 d8     7f
1c e0 ed a5     41 d6 61 c6 dc     c7
1c e0 ed a5     41 d5 61 c6 dc     fd
1c e0 ed a5     41 d4 61 c6 dc     eb
1c e0 ed a5     44 d6 61 c5 df     1c
1c e0 ed a5     44 d5 61 c5 df     26
1c e0 ed a5     44 d4 61 c5 df     30
1f e0 ed a5     42 d5 60 c3 e6     5c
1f e0 ed a5     42 d4 60 c3 e6     4a
1e e0 ed a5     55 d5 65 c7 e6     aa
1f e0 ed a5     41 de 61 c6 f7     2d
1f e0 ed a5     41 dd 61 c6 f7     17
1f e0 ed a5     41 dc 61 c6 f7     01
  • Probably a coincidence, but the second byte (0xD4 to 0xD6) gives a decimal value between 212 and 214, potentially within your range of 211 to 220 kPa. Do you have a part number or manufacturer for the sensor? – Cheibriados Dec 15 '15 at 15:49
  • @Cheibriados yes I have - it is VDO Continental S180052024 (FCC ID S180020, however the interesting parts are confidential in the FCC database) – Marki555 Dec 16 '15 at 8:35
  • Do you mean celcius degrees ? – w s Dec 17 '15 at 7:52
  • 1
    Inflate +100hPa, then drive slowly until you get the first measurements. Temperature will not be an issue if you just drive a couple of 100m... Point is: Make differential measurements for a differential analysis. – JimmyB Dec 27 '15 at 1:26
  • 1
    I would suggest learning the chip used in your TPMS. And then read about it's protocol in the datasheet. For example in NXP they transfer pressure and temperature. cache.freescale.com/files/training/doc/dwf/… see page 40 – Anton Kukoba Apr 23 '18 at 12:23
1

Usually, temperature and pressure only given by 1 byte of data. In my opinion, the first byte after ID is temperature in celsius and the second byte is pressure in kPa. The first byte which is in the range 41-55 can be calculated as follows: 1. Change hex to decimal. Hex 41 in binary is 65. 2. Substract 65 with minimum temperature that sensor is capable of (mostly -40). So 65-40 = 25 C. 3. To ensure your calculation, you must remove the sensor from the tire and test it in temperature controlled environment, e.g. fridge. Put the sensor in the fridge along side with digital temperature gauge. For the pressure, you don't need substraction because the sensor is not designed for vacuum calculation. Good luck.

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