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

particular bus type in a given vehicle. 
GMLAN buses use the Controller Area Network 
(CAN) communications protocol. Data is packaged 
into CAN messages, which are segmented into 
CAN frames. Each CAN frame includes header 
data (also known as the CAN Identifier, or CANId), 
and a maximum of eight (8) data bytes. A message 
may be comprised of a single frame, or multiple 
frames depending on the number of data bytes 
which defines the complete message. Data link 
arbitration occurs only over the header, or CANId, 
portion of a frame. 
Note:
See reference documents listed in Section 2 
for a detailed definition of the CAN Link. 
The GMLAN Enhanced Diagnostic Test Mode 
Specification is a GMW (GM Worldwide) document 
(also called GM Corporate) which defines 
diagnostic requirements for vehicle nodes and 
diagnostic testers. 
1.1 Scope. 
This specification establishes the 
Enhanced Diagnostics strategy for the GM 
In-Vehicle 
Local 
Area 
Network 
Subsystem, 
GMLAN. This strategy is required to 
be 
implemented by any node diagnosed on any of the 
GMLAN subnets. The strategy shall be tolerated by 
nodes connected to GMLAN subnets which are 
diagnosed via another means. 
1.2 Mission/Theme. 
The GMLAN diagnostic 
strategy shall provide a reliable, effective, and 
flexible means to diagnose ECUs and systems on 
vehicles equipped with GMLAN buses. The 
diagnostic services provided shall operate the 
same on all ECUs independent of subnet type, 
except where the diagnostic service affects the 
baud rate of the subnet. 
The GMLAN Enhanced Diagnostic Test Mode 
Specification has been targeted to the following 
objectives: 

Functional Based Diagnostic Approach to meet 
distributed system functionality over multiple 
ECUs and in-vehicle subnets. 

Meet diagnostic requirements of in-vehicle 
Virtual Networks and Virtual Devices. 

Harmonization 
of 
GM J2190 
and 
GM KWP2000 services as one global GM 
Corporate Standard. 

Reduction of total number of diagnostic 
services (test modes) and utilization of 
minimum amount of CAN Identifiers for 
Diagnostics. 

Optimized 
performance 
for 
testing 
and 
programming (e.g., parallel testing of ECUs on 
multiple subnets). 

Clear split by concept between dynamic 
real-time data retrieval and multiple frame 
static data messages (non time critical data).