Posted to Technical Tips Forum on 4/17/2016
Effects of Conditions on HS GM LAN (HS CAN) Bus
Some have asked what effects might be noted when using the
GM Data Bus Diagnostic Tool when various conditions occur.
The images in this post were captured from a pair of mock-up
boards used in training.
Note: I captured these shots using the DBDT and MDI a while
ago, before updates to the DBDT software and before my MDI 2
arrived. Since the software updates have increased the speed
approximately 25X, cleaner signals may be noted in future
A 2010 Camaro and a 2008 GMC Sierra are represented in the
graphs. Please bear in mind that these are mock-up boards,
not actual complete vehicles and not all modules may be
Adding or removing modules has an effect on the overall
shape of a graph, but what will be demonstrated here is the
general effect of grounding various Bus terminals, opening
or shorting to voltage.
This image represents an at rest [HS GM LAN] plot using
the DBDT of a normally operating system on the 2010 Camaro
HS GM LAN.
Here is [Diagnostic Data Bus Tool Graphs] the graph
when Bus + is grounded
Bus - grounded [Bus - Grounded].
This plot represents normal voltages when the 2008 Sierra HS
GM LAN (HS CAN) is active [Data Bus Normal]
Here is the "Detected State" for normal activity.
[Diagnostic Data Bus Tool "Detected State"]
This plot identifies the condition when a BCM connector was
disconnected at the BCM [Open Connector Graph] (Note
the plot scrolls from right to left of the display)
Here is the effect of removing the 120Ω Termination
Resistor during normal Bus activity. [Termination
This image identifies the effect of Bus - grounded [Bus -
Normal Bus activity [Normal Activity]
[Open HS GM LAN] shows the effect of a connector backed
out of the Electronic Brake Control module.
Here is the Measured Voltage scree with the Bus shorted to
B+ [HS GM LAN Bus Shorted to Voltage] and the Detected
State [Detected State Short to B ]
[Bus Shorted to Ground] demonstrates the effect of the
Bus shorted to ground.
Martin from British Columbia
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