Savana 3/4 Ton Van V6-4.3L VIN W (1998)
Information Bus: Description and Operation
Serial Data Communications
Class II Communications
The United States federal regulations require that all automobile manufacturers utilize a common serial data communications system. This system is
called the Class II communications system. The Class II communications system allows multiple signals, or messages to be carried on a single serial
data circuit.
The Diagnostic Executive
The Diagnostic Executive is the name given to a portion of the of the control module programming stored in the EEPROM. The functions of the
Diagnostic Executive are as follows:
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To monitor on-board diagnostic test status information
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To record on-board diagnostic test status information
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To record pending DTCs
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To record current DTCs
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To turn the MIL ON
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To store and erase Freeze Frame/Failure Records data
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To turn the MIL OFF
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To record History DTCs
Test Enabling Conditions
When the test enabling conditions for a particular test are met, the test will continue to run until one of the following occur:
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The conditions for enabling that test are no longer present.
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The test is completed and passed. In this instance the Diagnostic Executive will store the following information:
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The test has ran since the last ignition cycle.
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The test has passed during the current ignition cycle.
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A malfunction is not present at this time.
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The test is completed and failed. In this instance the Diagnostic Executive will store the following information:
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The test has ran since the last ignition cycle.
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The malfunction is present at this time.
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Certain engine data values present at the time of the malfunction.
Ignition Cycle
An ignition cycle consist of the following steps:
1. Start the engine.
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Some diagnostic tests require a warm-up cycle in order to run.
2. Operate the vehicle within the conditions for running the particular diagnostic test. The conditions required to run each test vary and may require
the following in order to run:
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A particular style of driving
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A certain amount of time
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A certain outside air temperature
