HOLDEN GEN III V8, Service Training

Page: 27 / 113

GEN III V8 ENGINE MANAGEMENT
SERIAL DATA COMMUNICATION (BUS MASTER)
Various devices; system control modules of the vehicle, as well as TECH 2 communicate with each other. The
communication between control modules and communication with the TECH 2 diagnostic scan tool is achieved
on the serial communication lines using serial data. Serial data transfers information in a linear fashion - over a
single line, one bit at a time. The serial data line is referred to as the 'data bus'. Excluding the GEN III V8 PCM,
all control modules communicating on the data bus communicate using UART communication.
DART is a 5 volt data line that toggles the voltage to earth (0 volts) at a fixed bit pulse width during
communication. UART transmits data at the rate of 8.2 kilobits per second (8192 bits/sec). With UART
communication, when there is no communication on the data line, the system voltage will be 5 volts.
The GEN III V8 PCM uses Class 2 communication.
This type of communication toggles the data line
from 0 volts to 7 volts at either a short or long pulse
width at a rate of 10.4 kilobits per second
(average). With Class 2 communication, when
there is no communication on the data line, the
system voltage will be 0 volts.
As the 'Class 2' communication is different to
UART (different languages), communication
between the modules is incompatible, and as such,
requires a Powertrain Interface Module (PIM) to
convert Class 2 communication into UART, and
UART into Class 2 (a translator).
TECH 2 is able to communicate with both UART
and Class 2 control modules.
On all VT and WH Models, the BCM is the Bus
Master of the serial data communication system.
The BCM periodically polls (surveys) each device
on the data bus and requests status data.
Page - 22 GEN III V8 ENGINE MANAGEMENT