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Thank you sir.
Not sure I'm following you here. Do you mean back probing all of the comm lines at the PCM? Or at each component?
I'm not sure how accurate or helpful this is. But while I was poking around with the DVOM, I tested pin #2 on the ODBII connector. (Which is supposed to be the comm + line.) And it's bouncing around from .47 to .88 volts.
Hmmmmm! That's weird. Wonder what caused that.
Just a quick update. I removed the PCM and pulled the cover. Don't smell anything burnt. And there are no obvious signs of any components under the protective gel getting hot.
Do you have communication with any other modules in the truck?
And I'm still unsure what you were looking at to determine there was no cranking rpm signal if you have no communication to the ecm.
The only tools that I have are a DVOM and an error code reader. So I don't have anything to communicate with any of the components. The code reader does have an RPM indicator. And I'm not getting a thing when I crank it.
OK, thanks for explaining that to me. I was hoping someone would have chimed in here. I really don't have any real practical experience troubleshooting this system. From what I was able to discern from the description and operation of the PCI bus, It is going to be difficult to see activity on the bus with just a multimeter. Also, I couldn't find the location of the Diagnostic Junction Port. That is where I would start the diagnosis if this thing ended up in my hands. (Someone please let me know if there's an easier way to do this.)
With a scope on each of the pins of this connector, there should be 0 to 7.v square waves, which is information being sent in binary.
A multimeter is too slow to see this activity, and will report an average of the voltage measured on the wire. So you're going to see some voltage lower than 7.5, but higher than nothing... I know, not very helpful so far.
Even the description of operation states that even with a scope, if you are seeing activity on the BUS, it does not guarantee that the information being sent isn't erroneous. It only verifies that that particular module is alive and talking
Another test I would likely perform would be a short to ground test.
With the modules unplugged, I would OHM test each pin of the connector to ground to make sure the harness isn't touching ground somewhere.
I wish I had more information you in this department, but that's about all I could think to test if I were in your shoes. Because you have no communication with the ECU, that leg of the bus seems most suspect to me, whether it ends up being a faulty module or comm line problem.
I remember in one of the early posts that the owner of the vehicle said he saw 5 Volts on the Pci Bus line at the obd2 connector I believe. Noah said it works on a 0 to 7 Volt square wave. So I would think your meter would only see half of this which would be 3.5 Volts. Your probably not going to like my next suggestion but I feel you need to do this. Computers can be expensive. You need to disconnect all the computers on the bus and check for continuity in the wires, and also make sure you don't have a cross circuit from a power source. It is possible you could have a cross circuit elevating your bus voltage. Don't know all the ins and outs of the system but it is possible. Also make sure none of the wires are shorted to ground. Hope this helps, kinda stinks when your not physically there to see the problem.
Thank you very much sir. I think I follow. Where can I find a wiring diagram for the continuity test? I have already unplugged each of these componets one by one hoping to find one that was shorted to ground. So I've still got all of the interior panels removed for access.
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