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Effects of Conditions on HS GM LAN (HS CAN) Bus
Posted to Technical Tips Forum on 4/17/2016 15 Replies

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 images.

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 present.

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 Resistor Removed]

This image identifies the effect of Bus - grounded [Bus - to Ground]

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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