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

WriteDataByIdentifier ($3B)
service to write any data which needs to be 
performed prior to executing a software reset. 
 
Note:
It may be necessary to perform multiple service $34/$36 sequences to download the data into the ECU 
(e.g., one sequence for each downloaded module). 
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GM WORLDWIDE ENGINEERING STANDARDS 
GMW3110 
© Copyright 2010 General Motors All Rights Reserved 
February 2010 
Page 278 of 336 
Certain steps may be required to be performed after a software reset of an ECU. When the utility file of an 
ECU reaches this point, the interpreter has to synchronize a software reset with all other interpreters running in 
parallel. At the point in time when each interpreter reaches the step in the utility file where the conclusion of the 
programming session is requested the tester shall conclude the programming event by transmitting a 
ReturnToNormalMode ($20) request message onto each GMLAN subnet (master execute). See Table 231. 
Table 231: Programming Procedure Conclusion 
Step 
Action 
26 
ReturnToNormalMode ($20)
using the AllNodes CANId with AllNodes extended address (to all links 
as required). If the tool has established the programming session on SWCAN then it must ensure that 
the service $20 is sent on this bus first so all ECUs on SWCAN can switch the baud rate before the 
MSSC ECUs reset and potentially cause errors (due to its transceiver being in low speed operation 
and all other nodes still in high speed operation).

The nodes do not respond to a mode $20 request if ProgrammingMode ($A5) service is enabled. 

Receipt of a $20 request causes the nodes to exit ProgrammingMode ($A5). 

Receipt of a $20 request also switches the low speed link back to low speed mode (if the 
programming event was performed in high speed mode). 

All nodes perform a software reset to enable execution of the new operational software and/or 
calibration and to synchronize communications startup. 
