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 99 of 336 
8.5 ReturnToNormalMode ($20) Service. 
The purpose of this service is to return a node or group of nodes to 
normal mode operation by canceling all active diagnostic services and resetting normal message 
communications (if they were interrupted by a diagnostic operation). 
All nodes participating in a GMLAN network shall support this service even if the node itself is diagnosed over 
another vehicle bus (e.g., KWP2000 or Class 2). This requirement is necessary to facilitate programming of 
other devices on the GMLAN subnet. 
8.5.1 Service Description. 
The following enhanced diagnostic services are terminated and/or reset by service 
$20: 

All levels of service $10 
InitiateDiagnosticOperation
are terminated. 

Service $27 
SecurityAccess
is terminated and a node shall become locked if the Manufacturers Enable 
Counter is $00 and the Vulnerability Flag (if implemented) is not $FF. 

Service $28 
DisableNormalCommunication
is terminated. 

All levels of service $A5 
ProgrammingMode
are terminated. 

Service $A9 
ReadDiagnosticInformation
send-on-change reporting of DTC count information is 
terminated. 

Service $AA 
ReadDataByPacketIdentifier
periodic message scheduler logic is reset. However, the node 
shall retain all dynamically defined message (DPID) information. 

Service $AE 
DeviceControl
is terminated, thereby returning full control of input(s)/output(s) to the node. 

Any ECU resources allocated for the DataTransfer ($36) service which were a result of receiving a 
RequestDownload ($34) request, shall be re-allocated back to their original purpose. 
In addition, if a request for this service is received during a programming session (activated via the $A5 
service), the programming session shall be considered concluded and all devices receiving the request shall 
perform a software reset. 
Note:
The software reset allows a device which had just been programmed to begin executing the new 
software and calibrations downloaded. The reset of all nodes also resynchronizes the start-up of normal 
communications. 
If a high speed programming event was enabled on the low speed SWCAN link when a request for this service 
is received, then all ECUs (including the tester) shall initialize their protocol converter hardware within 30 ms 
from the time that the $20 request is successfully transmitted on the link. The low speed ECUs shall perform 
the software reset after re-initializing the protocol converter hardware. If the low speed ECUs can reset the 
CAN controller and perform a software reset in less than 30 ms, the low speed ECUs shall reset the CAN 
controller immediately and delay the software reset the necessary amount of time to ensure that 
communication does not begin in less than 30 ms from the time that the $20 request is transmitted on the link. 
Note:
The delay is necessary to prevent bus errors that would occur if all nodes are not at the same baud rate 
when one node begins normal communication. 
Note:
Any node which uses a polling loop to service the protocol device shall ensure that the polling loop is 
fast enough to process the request message and initialize the protocol converter hardware within 30 ms. The 
reset of the protocol device shall take place prior to invoking the software reset. This is necessary to ensure 
that no timing issues exist with some nodes completing the reset and attempting to initialize normal 
communications before another device can initialize its protocol converter during its reset. 
When using this service to end a programming session, the tester must target the request at all nodes on the 
network via a functionally addressed request ($101 $FE $01 $20). A valid request for this service which 
concludes a programming event shall not be followed by a positive response. The positive response for this 
case has been eliminated due to timing issues involved with the possibility of transitioning back to the normal 
baud rate on the low speed subnet. 
If a request for this service is received while normal communications are disabled with the ($28) 
DisableNormalCommunications service, and a programming session is not active, then the node shall 
reinitialize normal communications. Reinitializing normal communications consists of the nodes application 
performing necessary tasks (e.g., resetting or clearing flags, variables, etc.) as needed, and then invoking the 
handler function(s) executed while in the Comm Init state. 
Note:
Refer to GMW 3104 and the Diagnostics And Node Management section of this specification for more 
details about the Comm Init state. 
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