Astra L4-1.8L (2009)
Information Bus: Description and Operation
Data Link Communications Description and Operation
Circuit Description
The communication among control modules is performed primarily through the GMLAN high speed serial data circuit and the GMLAN low speed serial
data circuits. The modules that need real time communication are attached to the high speed GMLAN network. The steering column control module
(SCCM) is the serial data gateway between the networks. The purpose of the gateway is to translate serial data messages between the GMLAN high
speed buss and the GMLAN low speed buss. The Local Interconnect Network (LIN) is another serial data communication network used on this vehicle
which is dedicated to the door/power windows subsystem. Below are more detailed descriptions of the individual networks. The gateway will interact
with each network according to that network's transmission protocol. Refer to Body Control System Description and Operation (Rear Electrical Center)
(See: Body and Frame/Body Control Systems/Description and Operation/Body Control System Description and Operation (Rear Electrical Center))Body
Control System Description and Operation (Steering Column Control Module) (See: Body and Frame/Body Control Systems/Description and
Operation/Body Control System Description and Operation (Steering Column Control Module))Body Control System Description and Operation
(Underhood Electrical Center) (See: Body and Frame/Body Control Systems/Description and Operation/Body Control System Description and
Operation (Underhood Electrical Center)) for more information about the gateway.
GMLAN High Speed Circuit Description
The data link connector (DLC) allows a scan tool to communicate with the high speed GMLAN serial data circuit. The serial data is transmitted on two
twisted wires that allow speed up to 500 Kb/s. The twisted pair is terminated with two 120 ohms resistors, one is internal to the engine control module
(ECM) and the other is after the vehicle communication interface module (VCIM). The VCIM is considered the DLC termination point of the link and
the ECM is the other end of the link. The resistors are used to reduce noise on the High Speed GMLAN buss during normal vehicle operation. The high
speed GMLAN is a differential bus. The high speed GMLAN serial data bus (+) and high speed GMLAN serial data (-) are driven to opposite extremes
from a rest or idle level. The idle level, which is approximately 2.5 volts, is considered recessive transmitted data and is interpreted as a logic 1. Driving
the lines to their extremes, adds one volt to the high speed GMLAN serial data bus (+) and subtracts one volt from the high speed GMLAN serial data
bus (-) wire. This dominant state is interpreted as a logic 0. GMLAN network management supports selective start up and is based on virtual networks. A
virtual network is a collection of signals started in response to a vehicle event. The starting of a virtual network signifies that a particular aspect of the
vehicles functionality has been requested. A virtual network is supported by virtual devices, which represents a collection of signals owned by a single
physical device. So, any physical device can have one or more virtual devices. The signal supervision is the process of determining whether an expected
signal is being received or not. Failsofting is the ability to substitute a signal with a default value or a default algorithm, in the absence of a valid signal.
Some messages are also interpreted as a heartbeat of a virtual device. If such a signal is lost, the application will set a no communication code against the
respective virtual device. This code is mapped on the Tech 2 screen as a code against the physical device. Note: a loss of serial data DTC does not
represent a failure of the module that the code is set in.
GMLAN Low Speed Circuit Description
The data link connector (DLC) allows a scan tool to communicate with the low speed GMLAN serial data circuit. The serial data is transmitted over a
single wire to the appropriate control modules. The transmission speed for GMLAN low speed is up to 83.33 Kb/s. Under normal vehicle operating
conditions, the speed of the buss is 33.33 Kb/s. This protocol produces a simple pulse train sent out over the GMLAN low speed serial data bus. When a
module pulls the buss high, 5 volts, this creates a dominant logic state or 0 on the buss. When the buss is pulled low, 0 volts, it is translated as a recessive
logic state or 1. To wake the control modules connected to the GMLAN low speed serial data buss, a high voltage wake up pulse is sent out over the
buss, the voltage level of the pules is +10 volts. Modules connected to the GMLAN low speed buss can be part of a virtual network as described in the
previous paragraph. The modules on the GMLAN low speed serial data buss are connected to the buss in a parallel configuration.
Local Interconnect Network (LIN) Description
The driver door module (DDM) and the front passenger door module (FPDM) communicate with window motors on the local interconnect network bus
1 and the local interconnect network bus 2 circuits respectively. The DDM LIN buss is connected to all window motors on its side of the vehicle, while
the FPDM LIN buss is connected to the other window motors. Communication on this network is only between the door modules and the window
motors. The window motors are in effect modules. The window motor modules do not communicate on any other data buss; therefore the door modules,
which also communicate on the low speed GMLAN serial data buss will perform all communication with each other, the motors, the SCCM (gateway)
and the scan tool including setting LIN buss DTCs.
Keyword 2000 Circuit Description
The keyword protocols utilize a single wire bi-directional data line between the module and the scan tool. The message structure is a request and
response arrangement. The keyword serial data line is used for scan tool diagnostics of the climate control seat module (CCSM) only. Other modules on
the vehicle do not exchange data on this circuit.
Data Link Connector (DLC)
The data link connector (DLC) is a standardized 16-cavity connector. Connector design and location is dictated by an industry wide standard, and is
required to provide the following:
