The DTC (Diagnostic Trouble Code) format is an automotive industry standard.  The format relies on two bytes to form an alpha numeric code.* 

You can setup a DTC signal if you set the Signal Type pulldown to DTC in the Edit Signal dialog (Figure 1).  Just select the Start byte where the DTC is located in the message and you're done! 

Some limits are placed on the dialog to help avoid mistakes.  DTC signals are byte aligned, so the Bit Position field is disabled.  DTC signals are 2 bytes long, so the Length is already set to this value for you.  To define the DTC further with a text description you can use a DTC Database.

Figure 1: Use the Edit Signal dialog to define a DTC signal in a message by selecting its Start Byte location.

*Gruesome Details of How a DTC is Defined by 2 Bytes (16 bits)
Byte #: |        Byte 1       |           Byte 2            |
Bit #:   0 1 | 2 3 | 4 5 6 7 | 8 9 10 11 | 12 13 14 15

Bits 0 & 1 - defines the only letter in the DTC.
00 = P = Powertrain
01 = C = Chassis
10 = B = Body
11 = U = serial data

Bits 2 & 3 - defines first digit of DTC.
00 = 0
01 = 1
10 = 2
11 = 3

Bits 4-7, 8-11, 12-15 - defines last 3 digits of DTC.
Uses Binary Coded Decimal (each group of 4 bits (nibble) = 0-9).

Table 1 illustrates an example of the translation between data bytes $92 $34 and DTC B1234.

Table 1: Example of DTC Translation

Vehicle Spy Documentation - (C) Copyright 1997-2011 Intrepid Control Systems, Inc.

Last Update: Tuesday, April 13, 2010