General Specification Electrical Function gmw3110 General Motors Local Area Network Enhanced Diagnostic Test Mode Specification

8.3.8 Tester Implications. 
This service should only be physically addressed (point to point). 
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GM WORLDWIDE ENGINEERING STANDARDS 
GMW3110 
© Copyright 2010 General Motors All Rights Reserved 
February 2010 
Page 94 of 336 
8.4 ReadDataByIdentifier ($1A) Service. 
The purpose of this service is to provide the ability to read the 
content of pre-defined ECU data referenced by a dataIdentifier (DID) which contains static information such as 
ECU identification data or other information which does not require 
real-time
updates. (
Real-time
data is 
intended to be retrieved via the ReadDataByPacketIdentifier ($AA) service.) 
8.4.1 Service Description. 
The request message shall always include one dataIdentifier. The length of the 
positive response message shall be adapted to the size of data referenced by the dataIdentifier parameter 
value. This message shall include the dataIdentifier parameter value received in the request message. 
The tester is only required to provide the dataIdentifier value desired. The target ECU is responsible for 
knowing the address location and block length corresponding to the requested DID. An ECU is not required to 
support all corporate defined DIDs, and may support additional application specific DIDs. 
Note:
Appendix C of this specification contains a list of corporate standard DIDs. 
8.4.2 Request Message Definition (Table 68). 
Table 68: ReadDataByIdentifier Request Message 
Data Byte Parameter Name 
Cvt 
Hex Value Mnemonic 
#1 
ReadDataByIdentifier Request Service Id 
M 
1A 
SIDRQ 
#2 
dataIdentifier 
M 
xx 
DID_ 
8.4.2.1 Request Message Sub-Function Parameter $Level (LEV_) Definition. 
This service does not use a 
sub-function parameter.