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

DeviceContol_Security_Level 
This is a flag used by the device control logic in determining the 
criteria for device control limits exceeded. If security is accessed, then 
the assembly plant device control restrictions are used. Otherwise, the 
restrictions imposed on service tools are used. Assembly plant device 
control restrictions are not required in all modules. If an ECU does not 
utilize assembly plant restrictions, then this variable defaults to 
SERVICE for the purposes of the pseudo code.
 
See Mode 
$27 
pseudo 
code 
ASSEMBLY_ 
PLT/SERVICE 
Security_Access_Allowed 
Indication that a valid security code as defined in the Vehicle Theft 
Deterrent SSTS has been received. 
FALSE 
TRUE/FALSE 
4 Diagnostic Strategy, Service Overview, and Implementation Rules and 
Requirements 
This section provides implementation rules which shall be followed by the Subsystem Leadership Teams 
(SSLT) of each platform organization. This section defines diagnostic message strategy, message 
identification, message addressing, and fundamental byte assignments for message frame types. 
4.1 Diagnostic Message Strategy - USDT and UUDT Messages. 
The Enhanced Diagnostic Test Mode 
Services utilize both Unacknowledged Segmented Data Transfer (USDT) and Unacknowledged Unsegmented 
Data Transfer (UUDT) messaging formats. 
The USDT format refers to those messages which may be segmented into multiple CAN transmission frames, 
depending on the number of data bytes transmitted. 
UUDT format refers to those messages which shall always be a single frame response. 
All diagnostic request messages and negative response messages use the USDT format, whereas positive 
response messages may be either USDT or UUDT format. Paragraph 4.2 contains a table which specifies the 
format of the positive response messages for each diagnostic service. 
The use of UUDT and USDT CAN Identifiers allows for interleaving of single frame responses (such as 
periodic data transmissions) with a multi-frame response (usually a one time data transmission) from the same 
node.