Electrical issues plaguing my life.

prattage

Member
Just bought this 2004 Tahoe AWD LT. Has all options excluding auto leveling suspension (premium smooth ride instead). Not a lot of these things work anymore.

The truck needed all brake lines when I got it. Installed Dorman brake line kit for stabilitrack vehicles. New calipers all around, everything bled out nicely. Next I turned to the cluster. Nothing here was working. Removed and "rebuilt" the cluster (re flowed most solder joints for resistors and voltage regulators), bench tested ok. Still nothing in the vehicle. No power at connector. This is when I found 4 broken wires under the under hood fuse box. Fixed these and everything is back to working order, or so I thought.

I have ELM327 device that would not connect to the truck. PIN 2 is showing ground. This should be network wire, not ground. Started digging deeper, splice pack sp205 is showing ground at PIN A and H. PIN A has two wires, 1 orange, 1 pink. Orange goes to radio, pink goes to SP207 and 5 more modules (have not located this splice pack yet). PIN H goes to splice pack SP206? The font is odd in my pdf so I cant read it well. This slice pack goes to 4 modules. I have also not dug into this splice pack yet. This is where I kind of stopped as this is becoming more work than I thought.

Now for what I find odd. With my DDM (driver door module) plugged in I cannot read codes/ communicate with the truck via OBD. as soon as I unplug the DDM I can communicate with the truck no problem. I followed some instructions from @TJBaker57 and my scanner is showing something like 500 codes. On my cheapo scan tool its showing just a P0420 code that comes and goes.
 

TJBaker57

Well-Known Member
So I will repeat what I posted in private message for the sake of others. With 500 lines returned I would guess you have sent out a request to every module on the vehicle to report the status of every code they each have knowledge of. I do this sometimes just for reference sake and then 'decrypt' that in a spreadsheet.

To request only current, pending, history with freeze frame available and codes requesting the MIL light from all modules the header should be set to "6C FE F1" and the request to send is "19 92 FF 00"
 

Mounce

Well-Known Member
Sounds like maybe the ddm is bad and disrupting the data bus?
 
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prattage

Member
Sounds like maybe the ddm is bad and disrupting the data bus?
I’m thinking the same. But would like to test it first. I thought that’s where I was getting ground in the data bus. But turns out I potentially have multiple other modules shorting to ground
 
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prattage

Member
I’m not finding any info on Google about how to test it. But I can say all functions work without issue.
 

Mooseman

Moderator
Door modules we usually just test by swapping them side to side. If the PDM works fine in the driver door and the DDM shorts out in the passenger door, then you know the DDM is shot.

Don't buy a new one, which will require programming. Just get a used one.
 
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prattage

Member
Any way you can paste a log file here of that output?
I cannot currently. Using an app on my phone with terminal without an option to log what’s input output of terminal. If I could find the correct program on my laptop I could do it that way.
 

TJBaker57

Well-Known Member
I cannot currently. Using an app on my phone with terminal without an option to log what’s input output of terminal. If I could find the correct program on my laptop I could do it that way.
What phone app are you using? I use an android app written by Kai Morich. "Serial Bluetooth Terminal". Has logging capabilities and also macro support that allows you to save those pesky setup strings and commonly used messages.
 

Reprise

Lifetime VIP Supporter
I use an android app written by Kai Morich. "Serial Bluetooth Terminal".
Just wanted to say 'thanks' for bringing this up. I found his Wi-Fi and USB versions; d/l'd all three to my phone.
 
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prattage

Member
I have an apple phone. Have yet to find a terminal app that will pair with my Bluetooth device. I will update as soon as I figure that out. This evening I should have time to try some more probing with the multimeter. Need to find out which module is grounding out my data bus.
 

TJBaker57

Well-Known Member
I have an apple phone. Have yet to find a terminal app that will pair with my Bluetooth device. I will update as soon as I figure that out. This evening I should have time to try some more probing with the multimeter. Need to find out which module is grounding out my data bus.
I'm not certain about this but I think I have read that iPhones have to use a wifi version of the obd2 adapters as they do not allow the use of Bluetooth serial port adapters?
 
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prattage

Member
I'm not certain about this but I think I have read that iPhones have to use a wifi version of the obd2 adapters as they do not allow the use of Bluetooth serial port adapters?
I believe this to be true now after some research.

I was doing some reading about the data line in the truck. This is supposed to be 5-7 volts at PIN 2 on DLC. I’m getting between .29-.79 volts. This is unaffected by DDM as nothing changes when it’s unplugged. Should I one by one unplug the module wires from the splice pack until I find the one causing these issues? Or would it be the ones that are showing ground

Also followed the wires a little deeper. At splice pack 207 I'm getting continuity to ground from PIN C & K. PIN C is "Vehicle Communication Interface Module". PIN K is "Digital Radio Receiver". So I guess will be looking into these modules whenever I get some time.
 
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TJBaker57

Well-Known Member
I believe this to be true now after some research.

I was doing some reading about the data line in the truck. This is supposed to be 5-7 volts at PIN 2 on DLC. I’m getting between .29-.79 volts. This is unaffected by DDM as nothing changes when it’s unplugged. Should I one by one unplug the module wires from the splice pack until I find the one causing these issues? Or would it be the ones that are showing ground

Also followed the wires a little deeper. At splice pack 207 I'm getting continuity to ground from PIN C & K. PIN C is "Vehicle Communication Interface Module". PIN K is "Digital Radio Receiver". So I guess will be looking into these modules whenever I get some time.


OK. So it is true that the serial data line voltage varies in that range, however, it varies so fast that a DMM cannot react fast enough to display that voltage. To truly see that voltage signal would require a scope. In my experience I have seen generally a range of no more than maybe a very brief 3 volts or so. Here is a youtube I made showing this..... The phone screen is displaying the data on the line. You can see when the trafic is low the voltage seen by the DMM is also low. When there is a flood of traffic the voltage seen by the DMM is higher.

 

TJBaker57

Well-Known Member
would it be the ones that are showing ground

None of the wires/modules on the serial data network should show continuity to ground. I have seen modules vary but I have never seen one lower than 10700 ohms. It is best to measure these serial data lines to ground with the battery disconnected as many, if not all of these modules are powered even with the key off.
 
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prattage

Member
Am I correct in assuming that this truck does not currently run?
Negative. I drive it daily. It actually runs great. Good power and shifts as it should. It just tells me to service stability and brake system every day. And then the red brake light will come and go as I’m driving. Abs light stay on steady. Also it’s the awd version. So it won’t go into 4-lo most of the time. One of the tccm codes is encoder motor
 
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prattage

Member
Just watched your video. Glad I did because I was thinking I’m still looking for a fault that doesn’t exist. But the ground showing up in the bus I know is an issue.
Wish I had a way to watch my data bus like that. I would try to put together a built in scanner for the truck using my raspberry pi lol
 

TJBaker57

Well-Known Member
With a running truck I would not spend a lot of time digging into the data bus with a DMM chasing an intermittent issue. My approach would be twofold,

1) get the codes. If the ABS light or other warning lights are coming on then there will be codes. The codes however will very likely be in the EBCM or BCM and TCCM for the 4WD, and most generic code readers won't get them. That can be dealt with though :wink:

2) I would record the traffic on the data bus and analyze what is happening. If a warning light is being turned on there should be message traffic indicating that. And if a module is dropping off that would be seen as well.

Maybe someone else with an iPhone can enlighten me, but as I understand it iPhone users need to use a wifi OBD2 adapter. And I think means they cannot connect to the internet through wifi while using the OBD adapter, but that shouldn't be an issue while driving.

The same seller of the Bluetooth OBD2 adapter I use also sells a wifi version.


There must be some serial terminal app for iPhone, no?
 

Mooseman

Moderator
Maybe someone else with an iPhone can enlighten me, but as I understand it iPhone users need to use a wifi OBD2 adapter. And I think means they cannot connect to the internet through wifi while using the OBD adapter, but that shouldn't be an issue while driving.
That is correct. Something about iOS blocking the extended functions in Bluetooth. That's why iOS don't have much for scanning apps. And if you do use a wifi adapter, you connect to it exclusively so no Internet unless you use cellular data.

There were a few discussions about iOS apps.
 
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prattage

Member
I currently use Car Scanner ELM OBD2 for my IPhone. Up until today I had not been using it correctly. I finally found out how to really scan the truck and now it is showing codes that I was only previously getting from the terminal.

Thank you guys for the help I'm going to continue to follow the ground issues in my data wire. I'll report back when I have more to share.

Let me know if this link works. This is what my scanner app is outputting now that I know how to use it correctly.

 
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Mooseman

Moderator
Good show. That showed some new ones that I have never heard of before. One stood out for me:
B2610
Raw code: A610
ECU: 40
Status: Pending fault present, Test has not been completed
Chevrolet: Passenger compartment dimming #1 (cluster, etc.) circuit malfunction; Passenger Compartment Dimming 1 Circuit Short to Ground
I'd concentrate on this. However it could be a red herring since it's part of the BCM and there are other modules throwing codes which could be a result of the bus' short to ground. I think you're going to wind up pulling the comb from the data bus splice and testing one circuit at a time until you find the shorted one.
 
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prattage

Member
Good show. That showed some new ones that I have never heard of before. One stood out for me:

I'd concentrate on this. However it could be a red herring since it's part of the BCM and there are other modules throwing codes which could be a result of the bus' short to ground. I think you're going to wind up pulling the comb from the data bus splice and testing one circuit at a time until you find the shorted one.
Guess I just assumed that code was the dead bulbs in my cluster and the HVAC controls. I’ve pulled the combs out of both SP205 and 207 and found the modules or at least the harness going to them showing ground. I removed the digital radio receiver last night. That was the old XM module, this was one shorting to ground. As long as the weather cooperates I’ll have it sorted this weekend I think.
 

TJBaker57

Well-Known Member
I currently use Car Scanner ELM OBD2 for my IPhone. Up until today I had not been using it correctly. I finally found out how to really scan the truck and now it is showing codes that I was only previously getting from the terminal.

Thank you guys for the help I'm going to continue to follow the ground issues in my data wire. I'll report back when I have more to share.

Let me know if this link works. This is what my scanner app is outputting now that I know how to use it correctly.



Excellent use of the Car Scanner app there! You have shown that it can read codes from other modules, specifically you have codes for the TCCM (address 1A) and the airbags (address 58) as well as the BCM.

I have a PID for the dimming input to the BCM and some other dimming PIDs for my 2005 Yukon with P59 PCM. They might work for your 2004.
 

txtaz

New Member
I always clean and tighten all my ground connections whenever something "Odd" happens. There are dozens of ground connections and one bad intermittent one can cause a real headache finding it. Because I run large amps in my Yukon, I have 4 and 0 gauge ground wires tying the frame and body to the alternator and battery.
Good luck.
 

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