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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