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

GM WORLDWIDE ENGINEERING STANDARDS 
GMW3110 
© Copyright 2010 General Motors All Rights Reserved 
February 2010 
Page 148 of 336 
Procedure 3: 
1. If the ECU supports the use of the negative response code $78, then send a request under conditions 
which would cause the $7F $2C $78 to be sent. Verify that the negative response is sent and that the 
appropriate last response is sent within the P2
C
* timing criteria. 
8.10.8 Tester Implications. 
1. The test device may assume the contents of dynamic DPIDs are retained upon a $3E time-out or after a 
$20 service request. 
2. If the tester redefines a DPID without stopping the scheduler, the PIDs in the response message may not 
be correct until the 2nd response of that message. This is the case because a message may be queued 
for transmission at the time the DPID is being redefined and may not gain access to the link until after 
successful completion of the $2C service. 
3. This service should only be requested with physical addressing. 
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GM WORLDWIDE ENGINEERING STANDARDS 
GMW3110 
© Copyright 2010 General Motors All Rights Reserved 
February 2010 
Page 149 of 336 
8.11 DefinePIDByAddress ($2D) Service. 
The purpose of the $2D DefinePIDbyAddress service is to provide 
the ability to map ECU variables to a dynamic Parameter Identifier (PID) using ECU memory addresses. The 
resulting PID defined by this service can then be requested via diagnostic service $22 or diagnostic service 
$AA. 
Note: 
To retrieve a PID via the ReadDataByPacketIdentifier service the PID must first be packed into a 
dynamic DPID using the $2C service. 
This service ($2D) supports defining a single PID per request (multiple PIDs can be defined in a given ECU, 
using multiple requests). 
This service is intended for use during a device
’s development cycle to allow access to data that may not be 
available via another diagnostic service. This service is only intended for use in engineering development. It 
will not be used in field service applications.