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 7 of 336 
1 Introduction 
Note: 
Nothing in this standard supersedes 
applicable laws and regulations. 
Note: 
In the event of conflict between the English 
and domestic language, the English language shall 
take precedence. 
General Motors in-vehicle Local Area Network 
(GMLAN) is a family of serial communication buses 
(subnets) which enable Electronic Control Units 
(ECU) or nodes)) to communicate with each other, 
or with a diagnostic tester. 
GMLAN supports three bus types; dual wire high 
speed controller area network (HS-CAN) buses, 
dual wire mid speed (MS-CAN) buses, and single 
wire low speed (LS-CAN) buses. 
High speed buses (500 kilobits per second (kbps)) 
are typically used for sharing real time data such 
as driver commanded torque, actual engine torque, 
steering angle, etc. Examples of High speed buses 
are, but not limited to, the Primary HS bus, the 
Chassis Expansion bus, and the Powertrain 
Expansion bus. 
Mid speed buses (approximately 95.2 kbps or 
125 kbps) are typically used for infotainment 
applications (display, navigation, etc.) where the 
system response time demands that a large 
amount of data be transmitted in a relatively short 
amount of time, such as updating a graphics 
display. An example of a mid speed bus is the 
Primary MS bus. 
Low speed buses (33.33 kbps) are typically used 
for operator-controlled functions where the system 
response time requirements are of the order of 
100 to 200 ms. These buses also support high 
speed operation at 83.33 kbps used only during 
ECU reprogramming. An example of a Low speed 
bus is the Primary LS bus. 
The decision to use a particular bus in a given 
vehicle depends upon how the feature/functions 
are partitioned among the different ECUs in that 
vehicle. There may be more than one network of a