2004 Sierra 2500 6.0 no comm with scanner

gmtec2

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Nov 27, 2021
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Indina
I just bought a 2004 GMC Sierra 2500 with 6.0. Took it for a ride and runs great. Driving home and the CEL came on. I came home and hooked my Matco scanner up, can't communicate with the truck. Work car and wifes car work so I doubt the scanner. Checked pins 2 & 5 for voltage and it jumps from 1-3 volts, not 5-7. I still need to double check all fuses and power to grounds but what I'm really looking for is the schematic for the module locations and wiring schematics. I did see some schematics that I printed but they appeared to be for a 1500 5.3. If there is any pointers/advice? I'm pretty confident in my electrical troubleshooting but don't have access to a GM tech 2 or a snap on scanner to see what modules may be an issue. Thanks in advance, Dave
 

TJBaker57

Member
Aug 16, 2015
2,897
Colorado
I just bought a 2004 GMC Sierra 2500 with 6.0. Took it for a ride and runs great. Driving home and the CEL came on. I came home and hooked my Matco scanner up, can't communicate with the truck. Work car and wifes car work so I doubt the scanner. Checked pins 2 & 5 for voltage and it jumps from 1-3 volts, not 5-7. I still need to double check all fuses and power to grounds but what I'm really looking for is the schematic for the module locations and wiring schematics. I did see some schematics that I printed but they appeared to be for a 1500 5.3. If there is any pointers/advice? I'm pretty confident in my electrical troubleshooting but don't have access to a GM tech 2 or a snap on scanner to see what modules may be an issue. Thanks in advance, Dave

Test voltage between OBD2 pin 16 and either a ground or OBD2 pins 4 and/or 5. Pin 16 should be battery voltage to power the scanner.
 
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TJBaker57

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Aug 16, 2015
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What are the work vehicle and the wifes' vehicle? 2008 or newer? They would be using ISO 15765-4 CANBUS where this 2004 you just got is likely SAE J1850 VPW. I don't imagine that helps much but if either the work or wifes' vehicle were also J1850 VPW that would at least prove the scanners J1850 interface is functional.
 
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gmtec2

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Nov 27, 2021
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Indina
What are the work vehicle and the wifes' vehicle? 2008 or newer? They would be using ISO 15765-4 CANBUS where this 2004 you just got is likely SAE J1850 VPW. I don't imagine that helps much but if either the work or wifes' vehicle were also J1850 VPW that would at least prove the scanners J1850 interface is functional.
Sorry, my work car is a 2000 Malibu and hers is a 2009 Traverse
 

TJBaker57

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Aug 16, 2015
2,897
Colorado
Checked pins 2 & 5 for voltage and it jumps from 1-3 volts


In observations on my own 2002 4.2 TrailBlazer a 0 to 3 volts read from pin 2 seems normal. Most every DMM I have used simply cannot respond/read fast enough to display the true state of the serial data bus.
 
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TJBaker57

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Aug 16, 2015
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Do you happen to own one of those inexpensive OBD2 adapters, usually Bluetooth but sometimes WiFi? These usually have the ability when given the proper command, to display all discernable traffic on the serial data bus. Might yield a clue.

Otherwise, I imagine somewhere on that Sierra is a data bus splice pack where the various modules can be isolated in order to discern which module(s) may be causing a disruption.
 
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gmtec2

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Nov 27, 2021
12
Indina
Do you happen to own one of those inexpensive OBD2 adapters, usually Bluetooth but sometimes WiFi? These usually have the ability when given the proper command, to display all discernable traffic on the serial data bus. Might yield a clue.

Otherwise, I imagine somewhere on that Sierra is a data bus splice pack where the various modules can be isolated in order to discern which module(s) may be causing a disruption.

I will look into the Bluetooth adapters. I thought they were basic code readers. I read to look at the split pack but didn’t know how I would find the problem without an oscillator or high end scanner. Thanks for pointing me in the right direction.
 

Reprise

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One other thing you might check, since it affects writing to the PCM (when I update through HPTuners), and you can do this easily.

Does your truck have an aftermarket radio? If it does, pull the fuse to disable it, and see if that helps with reading from the Matco.

If your truck has the stock radio, disregard.

As for schematics... we have the service manuals available for download, and they're in there. Look for any of Mooseman's posts; he has the links in his signature.
 

gmtec2

Original poster
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Nov 27, 2021
12
Indina
One other thing you might check, since it affects writing to the PCM (when I update through HPTuners), and you can do this easily.

Does your truck have an aftermarket radio? If it does, pull the fuse to disable it, and see if that helps with reading from the Matco.

If your truck has the stock radio, disregard.

As for schematics... we have the service manuals available for download, and they're in there. Look for any of Mooseman's posts; he has the links in his signature.
I did try that still same result. It gets stuck on ISO 9161-2 after keyword 2000
 

gmtec2

Original poster
Member
Nov 27, 2021
12
Indina
Do you happen to own one of those inexpensive OBD2 adapters, usually Bluetooth but sometimes WiFi? These usually have the ability when given the proper command, to display all discernable traffic on the serial data bus. Might yield a clue.

Otherwise, I imagine somewhere on that Sierra is a data bus splice pack where the various modules can be isolated in order to discern which module(s) may be causing a disruption.
Does anyone happen to recommend a OBD2 Bluetooth dongle that will show a waveform by chance?
 

azswiss

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May 23, 2021
861
Tempe, AZ
PID graphing is managed by the app (e.g. Torque Pro), not the dongle. Even then, only specific PID's recognized by the system can be tracked. If you want to capture waveforms of arbitrary variables (e.g. voltage or current at a specific point in the harness) then you will need something along the lines of the equipment described in the following link by @MRRSM : How To Use PICO #2204A & HANTEK #1008C Oscilloscopes
 

gmtec2

Original poster
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Nov 27, 2021
12
Indina
PID graphing is managed by the app (e.g. Torque Pro), not the dongle. Even then, only specific PID's recognized by the system can be tracked. If you want to capture waveforms of arbitrary variables (e.g. voltage or current at a specific point in the harness) then you will need something along the lines of the equipment described in the following link by @MRRSM : How To Use PICO #2204A & HANTEK #1008C Oscilloscopes
Thanks for the info.
 

TJBaker57

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Aug 16, 2015
2,897
Colorado
will look into the Bluetooth adapters. I thought they were basic code

They are an interface to the network. The capabilities are mostly limited by the app you choose. The dongles I have also have a bus-monitoring mode where they just stream everything seen on the data bus. In this mode we could see whatever is happening on the network. Plus we have more control of what the dongle does, like we can instruct it to use SAE J1850 VPW in this case. (I am assuming your vehicle is J1850 VPW, if your OBD2 port has terminals in just pins 2, 4, 5, & 16 thats pretty much a dead giveaway that it's J1850 VPW.)

The raw data won't mean anything to you but I can read it and we might gain some insight as to what's happening on your truck.
 

gmtec2

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Nov 27, 2021
12
Indina
They are an interface to the network. The capabilities are mostly limited by the app you choose. The dongles I have also have a bus-monitoring mode where they just stream everything seen on the data bus. In this mode we could see whatever is happening on the network. Plus we have more control of what the dongle does, like we can instruct it to use SAE J1850 VPW in this case. (I am assuming your vehicle is J1850 VPW, if your OBD2 port has terminals in just pins 2, 4, 5, & 16 thats pretty much a dead giveaway that it's J1850 VPW.)

The raw data won't mean anything to you but I can read it and we might gain some insight as to what's happening on your truck.
Ok so which app do you recommend? I was looking at a different scanner since mine is from early 2000s when I wrenched cars. If j can get a dongle and a good app, I’m all for it.
 

gmtec2

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Nov 27, 2021
12
Indina
Do you see it try SAE J1850 VPW?? Can you set it to use that? I am fairly certain that is what you need.
No I cannot manually adjust. It’s from early 2000s and didn’t have advanced scanners back then. That’s why I was trying to figure out something that would be decent to troubleshoot the current issue and be useful in the future as I wrench on the side.
 

TJBaker57

Member
Aug 16, 2015
2,897
Colorado
No I cannot manually adjust. It’s from early 2000s and didn’t have advanced scanners back then. That’s why I was trying to figure out something that would be decent to troubleshoot the current issue and be useful in the future as I wrench on the side.


I would be quite surprised if an early 2000s scanner didn't support J1850 so I would guess that for some reason it is getting stuck on an incorrect protcol maybe. I see GM did have a handful of vehicles that used ISO9141 according to pinoutguide.com but not your truck. As a possibly related curiosity, pinoutguide.com lists about 8 or 10 vehicles as using a protocol they call "VPN". Your 2000 Malibu among them. The odd thing is that there does not appear to exist any such protocol!! I can't figure that one out.

Have a look at your OBD2 ports in both the Mailbu and the truck to verify which pins have terminals wired to them.

There was a SAE specification, J1978, that gave an order for the scanning of protocols that scan tools should use in connection attempts...

Screenshot_20211129-080706.png

The apps that I use all do the same thing when scanning for a connection which is to send out a message requesting the listing of what standards PIDs are supported in the range of 0x00 to 0x20. They will do this for a time and if no response from the ECM/PCM they try the next protocol they support. If your Matco follows the same procedure and follows the SAE order then it looks like it is moving beyond the J1850 which suggests it isn't getting response it expects to see.
 

TJBaker57

Member
Aug 16, 2015
2,897
Colorado
Ok so which app do you recommend? I was looking at a different scanner since mine is from early 2000s when I wrenched cars. If j can get a dongle and a good app, I’m all for it.

I am not schooled on todays (or even yesterday's) scanners so look to others for recommendations for possibly updating your Matco. In a general sense you have to address what your expected needs are or will be. Range of vehicles, cost, etc., that sort of thing.

I see these inexpensive Bluetooth adapters as offering capabilities that I have not seen in any other "scanner" at any cost. And this at a cost of less than a decent lunch. Now the flip side is that these little adapters don't do all this at a simple push of a button or two. They need an app do the talking for you and most all the apps are targeting the mass market user who just wants to read a code or maybe look at some live data. For advanced interactions one has to either study up or find someone who knows how to do it. If your case is as I expect then you need someone who knows the GM class 2 serial data network with SAE J1850 VPW protocol and that is my niche. I do not know squat about other protocols as both of my vehicles are J1850 VPW so that is where my research led me.


So for the adapter I use this one (of which I have 3) which has been reliable for me...


And for a hands-on app for interacting with the network I use free Android app called Serial Bluetooth Terminal by Kai Morich. This app is not specifically for vehicles, it is just for sending and receiving and recording data on a serial connection.


There are a host of apps for reading codes, displaying and recording live data, etc. For Android I have Torque Pro, Car Scanner, OBD Fusion, DashCommand, Car Gauge Pro, and so on. I would recommend not getting any of these just yet, but rather just the Bluetooth adapter and the free Serial Terminal app that may allow you (us) to figure out why your Matco doesn't connect.
 

gmtec2

Original poster
Member
Nov 27, 2021
12
Indina
I would be quite surprised if an early 2000s scanner didn't support J1850 so I would guess that for some reason it is getting stuck on an incorrect protcol maybe. I see GM did have a handful of vehicles that used ISO9141 according to pinoutguide.com but not your truck. As a possibly related curiosity, pinoutguide.com lists about 8 or 10 vehicles as using a protocol they call "VPN". Your 2000 Malibu among them. The odd thing is that there does not appear to exist any such protocol!! I can't figure that one out.

Have a look at your OBD2 ports in both the Mailbu and the truck to verify which pins have terminals wired to them.

There was a SAE specification, J1978, that gave an order for the scanning of protocols that scan tools should use in connection attempts...

View attachment 102297

The apps that I use all do the same thing when scanning for a connection which is to send out a message requesting the listing of what standards PIDs are supported in the range of 0x00 to 0x20. They will do this for a time and if no response from the ECM/PCM they try the next protocol they support. If your Matco follows the same procedure and follows the SAE order then it looks like it is moving beyond the J1850 which suggests it isn't getting response it expects to see.
You are correct. It seems to be going from one protocol to the next, getting through all of them with no comm. I’m borrowing a scanner tonight and I will check with his. He said it was a OTM?
 

TJBaker57

Member
Aug 16, 2015
2,897
Colorado
You are correct. It seems to be going from one protocol to the next, getting through all of them with no comm. I’m borrowing a scanner tonight and I will check with his. He said it was a OTM?

Cannot find anything on "OTM" scanner. Guess we will find out!

Edit: Just to cover the most basic of questions: the key is turned ON when your scanner is scanning, right?
 

Mooseman

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Dec 4, 2011
25,262
Ottawa, ON
Probably meant OTC.
 

gmtec2

Original poster
Member
Nov 27, 2021
12
Indina
Well he forgot the scanner every day those week(he’s older) so I bought a new one. Tried scanning and every module is “not equipped” I bought a Launch and not sure if I like it yet but did a scan on my wife’s car and worked good. I’ll start chasing my tail tomorrow with modules and grounds
 

Yeagamyster04

Member
Oct 8, 2021
22
Davison michigan
My brother in law had same problem turned out being blown fuse. Replaced fuse under hood and worked after that. Give that a look
 

gmtec2

Original poster
Member
Nov 27, 2021
12
Indina
My brother in law had same problem turned out being blown fuse. Replaced fuse under hood and worked after that. Give that a look
I do already have power at the OBD. Checked all fuses already. I ordered a new scanner and will be here this week. I will try more troubleshooting when I’m off later in week.
 

mrrsm

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This is an unusual Diagnostic Discovery that is worth investigating for No OBD2 Comms:


...and another similar Truck with No OBD2 Comms worth watching:


Check Out @Realism 's Famous Thread on Grounds for a Ready Reference that is worth visiting from time to time. he shows Where to find the Grounds and Bonding Straps to R&R, Clean Up, Paste Up with Dielectric Grease and Re-Attach any that might be the cause of this NO OBBD2 Comms problem:


Since you are self-described as being "Electrically Astute", Snap-On has two comprehensive On-Line Zoomed Training Videos linked below that will help in figuring out What to Look for, Where to find things and What Tools to use to help Diagnose and Repair Failed Class 2 and CAN Bus Networks:

Part 1:

Part 2:
 

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