Tech 2 Purchase

[Sparksalot]

Sounds like MX OBDLink and BlueDriver have full diagnostics capabilities. So it's just a matter of preference. Although BlueDriver claims they provide suggested fixes. @Sparksalot you have one, what do you think about their claims:

It gives you a starting point. You can also use it to see historical info and codes. Also reset them.

 

[gooffeyguy]

I have an OBDLink MX for sale in the classifieds

 

[George B]

Just placed an order for another VCI module. Will try and see if it works better or differently.

 

[TJ Baker]

@George B

With the Envoy, have you any other
systems not always working just right? Symptoms of a bad ground maybe? I don't think you do or at least you haven't mentioned any.

However, I once read of a fellow who posted pictures of OBD2 port and OBD2 adapter that had 'shorted out' and partially melted. From the picture it could be seen that the apparent path of current involved only the 2 ground circuits. Turns out that on the GMT360 these 2 ground circuits, pins 4 & 5 of the OBD2 DLC connection, go to two different chassis ground points. Both of these ground points serve multiple systems and each has a splice point or two where their respective systems are collected before going on the ground point.

So if a vehicle had a poor or weak ground at one these 2 ground points the systems served by that ground might present an occasional glitch. The two ground pins are isolated at the DLC connector, until someone plugs in a scantool which may offer a path between pins 4 and 5. If a path then exists, the systems operating on the weaker ground point may seek a ground path through the scantool to a better ground point on the other DLC terminal. In the case of the thread I refer to the owner discovered that when he had the carpet replaced the G201 ground beneath the carpet was not resecured well, creating an intermittent ground. The HVAC blower was the big draw that ran through his DLC, through the scantool, and out the other ground, causing an overcurrent through the DLC connector that was never intended for that kind of current.

So why is this pertinent here?? It just bugs me that your cluster resets, like its power was lost momentarily. And the cluster uses both of the same grounds as the DLC connector. The cluster uses G201 for the lighting and it uses G102 for the electronics.

 

[George B]

@TJ Baker
The envoy exhibits no other symptoms. It only does this when the tech2 is connected and booting up. Or during SPS info collection.

 

[TJ Baker]

@TJ Baker
The envoy exhibits no other symptoms. It only does this when the tech2 is connected and booting up. Or during SPS info collection.

Very strange. To the best of my knowledge there is nothing that will cause the cluster to reset except a power cutoff. No scantool command, no loss of serial data connection, and so on.

 

[George B]

Very strange. To the best of my knowledge there is nothing that will cause the cluster to reset except a power cutoff. No scantool command, no loss of serial data connection, and so on.

Here is a video I made. I also snapped photos of the codes produced. Is there a way to test if the VCIM of the Tech2 is shorting the serial data side to ground?

 

[TJ Baker]

Here is a video I made. I also snapped photos of the codes produced. Is there a way to test if the VCIM of the Tech2 is shorting the serial data side to ground?

I will do some retesting today. Just by looking at the video I would say the gauge sweep to zero you have there is NOT a cluster reset of the sort that I have seen from a power loss. A power loss reset I think moves all needles to zero much more rapidly.

I have recently tried a 'short to ground' of the serial data line and I don't think it did what yours is doing. But I want to recheck.

The codes make it clear... something IS fouling the data bus. You are reading the PCM saying that it has lost comms with those modules. The "Unknown Driver" message is a direct result of a loss of comms between the BCM amd the instrument cluster.

 

[TJ Baker]

Here is a short video of me grounding out the data bus and the results seen at cluster and on the message stream as well.

Grounding the GM Class 2 Serial Data Bus

Here I show the effect of grounding out the GM class 2 Serial Data bus. Note that the cluster doesn't reset, it only stops updating. On the phone screen seen...

youtube.com

 

[George B]

Here is a short video of me grounding out the data bus and the results seen at cluster and on the message stream as well.

Grounding the GM Class 2 Serial Data Bus

Here I show the effect of grounding out the GM class 2 Serial Data bus. Note that the cluster doesn't reset, it only stops updating. On the phone screen seen...

youtube.com

I guess it’s a mystery until we can see what the tool is doing when booting. I am hopeful my new VCI works differently and that I can send you the goofy one for testing. It would be interesting to see what is going on.