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Posted to Technical Tips Forum on 10/10/2014 24 Replies

This is intended for those who are interested in CAN Bus exploits.

Coming soon (possibly next week) to North American GM dealerships near you, is the GM "Data Bus Diagnostic Tool".

I had the opportunity to download the program via TIS2Web this week and try it out on a couple of vehicles. The vehicle of choice for this post is a 2014 Chevrolet Silverado 1500 4WD truck, into which faults were inserted to view the program in action. However, the vehicle itself is not the real focus, but the Data Bus Diagnostic Tool (DBDT) may be of interest.

The main intent of the tool is to assist technicians in diagnostic direction and proficiency.

Let's begin by identifying how the program is started once downloaded. Data Bus Diagnostic Tool shows the main features of the home screen. Not shown is a single cursor.

Rather than attempt to explain all of the features (and to be quite honest, I have not had time to explore the program extensively since my free time is a premium), what follows will be a basic program overview as an introduction.

Once downloaded via TIS2Web, the program is accessed via a desktop shortcut. When the window opens, a very simple screen is displayed with some selectable tabs across the header, selectable bus type with baud type identified and a row of control buttons across the bottom of the screen. Nothing will happen unless the green power button is clicked, at which point the button changes to a red X used to close the program.

The Data Bus Diagnostic Tool uses the MDI as the interface, so if GDS 2 is hogging the MDI, it must be disconnected to allow the DBDT to identify and utilize the MDI, which will be identified. No MDI

It is no create surprise that the speaker button allows the program to feedback an audible tone that sounds quite similar to the screech of a logic probe when used to test a data bus. There is an option to have the beeper tone present during the presence of a bus fault or when the bus is functioning normally. To the right of the display area tool bar, is the familiar system voltage sign. Note that the KOEO voltages were low; only because the truck has sat unused since early June, save for being moved once in a while.

The photos are annotated to be fairly self-explanatory, but if the MDI is not connected, or is assigned to another program as aforementioned, it must be connected to the DBDT. There is an option to select devices, so I have no idea whether alternatives to the MDI will work, since I have not had the chance to try any.

This photo demonstrates the program in action with the vehicle KOEO. Normal Bus Function Normal HS GM LAN (CAN) voltages

In subsequent screens a simple fault will be introduced, to see how quickly the program reacts to a failure. The various states and time stamps from normal to failures and back to normal function on the bus will be displayed. Bus Detected State

The fault was introduced into the circuit at the under hood fuse box, by removing fuse # 57, which is an ATC 3-Leg Micro Blade fuse, which happens to feed both the ECM and TCM. As expected and can be noted in this photo, Also noted in the next photo is the change in the bus signal. HS LAN Bus fuse 57 reinstalled ECM and TCM back on line

This was done a few times in succession with consistent results during both KOEO and KOER. Turning the ignition off, the bus voltage began stepping down and when the key was turned back on, the voltage immediately rose to normal. HS LAN going to sleep

Now, I'm not overly worried about "bricking" a module, since we have only experienced a single module failure in many years. However, the next photo A Failure depicts a real failure on the bus. While viewing the effect of the fuse removal and reinsertion, someone happened to open the driver's door and the Bus Hi voltage dropped to 0 volts, as can be seen in here in the Measurement screen Bus Hi at 0 volts and is verified in the Detected State screen. Bus State

All module communication with the tool was lost, while the truck still ran, although when the rpm was raised, throttle control resulted in unstable flaring.

The bus Hi voltage moved from an initially unstable state to 0 volts from this time until proper function was restored. Powering down the DBDT and once connected, GDS 2 would no longer read or decode the VINas it would normally in this photo. GDS 2 When entering the VIN # manually, no communication was the result. Letting the truck go to sleep had no effect and neither did disconnecting the battery and connecting the cables together. I was pretty sure that the issue was in the ECM, but I had to head home for the day, since this was all done well on my free time.

At 4:45 am this morning I disconnected the ECM [2014 Chevrolet Silverado 1500 LT, ECM/Inputs/Outputs Photo] and waited a few minutes, then reconnected the three ECM connectors. Subsequently, normal data bus function was restored as was viewed on the DBDT. Scanning the system with GDS 2, resulted in DTCs stored in many modules as expected Bus function restored, GDS 2 display , which were then cleared, as shown here. DTCs cleared

Martin from British Columbia

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