LIN diagnostic frames shall always use checksum calculation of protocol version 1.

[ChrisPHL]

in lin.cpp, line 124 should be exchanged to accomplish this automatically:

  // LIN diagnostic frame shall always use CHKSUM of protocol version 1.
  uint8_t cksum = dataChecksum(message, nBytes, (proto == 1 || addr == 0x3C) ? 0 : addrbyte);

Line 182 accordingly ;-):

    // LIN diagnostic frame shall always use CHKSUM of protocol version 1.
    if (proto == 1 || addr == 0x3D) idByte = 0; // Don't cksum the ID byte in LIN 1.x