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

5.2.3.2 Application Triggered Diagnostic VN. 
To ensure that a node remains in the COMM_ACTIVE state 
while a tester is performing diagnostic services, all nodes (which support the diagnostic services described in 
this specification) shall support an application triggered diagnostic VN. 
The application triggered diagnostic VN shall be activated and deactivated by the node
’s diagnostic application 
layer. Since the application triggered diagnostic VN is local to each node, no Virtual Network Management 
Frame (VNMF) activation bit shall be transmitted in support of this VN. 
The Application Layer shall use the service primitives provided by the Network Layer and additional 
self-generated flags to determine if an activation or deactivation of the application triggered diagnostic VN is 
required. 
5.2.4 Enabling Diagnostic Communications. 
To begin performing diagnostic services, a tool sends out a 
wake-up request (for SWCAN this is the high voltage wake-up with CANId $100, for wake-up mechanisms on 
other GMLAN links, the tool uses the InitiateDiagnosticOperation service sub-function $04 - wakeUpLinks 
targeted to all gateway devices using a functionally addressed request with the Gateway Devices - $FD 
extended address). The wake-up causes ECUs to transition into (or remain in) the COMM_ACTIVE state. An 
ECU which was previously in the COMM_KERNEL_INACTIVE state (see Figure 9) would transition through 
the COMM_INIT state and through the COMM_ENABLED state (due to the initially active diagnostic VN) and 
end up in the COMM_ACTIVE state. The diagnostic CAN Identifiers are enabled in the kernel as long as the 
initially active diagnostic VN is active (8 s). 
While the initially active diagnostic VN is active, the tester can activate the application triggered diagnostic VN 
in order to keep the ECU in the COMM_ACTIVE state while it is performing diagnostics. 
Figure 11 contains a state transition diagram of the diagnostic application. The following definitions are 
provided to aid in understanding the requirements for transitioning into and out of the various states: