2003 Tahoe, lots of electrical gremlins

SveinHa

SveinHa

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Location
Carten Island, Norway
I just bought a 2003 Tahoe that have been out of service for 5-6 years. It starts and runs well and I got it home yesterday (100km/60miles including a few long 8% slopes). There are so many electrical problems that I assume there are one or a few key problems that needs solving like grounding problems or similar. 10-15 years ago, I had a 2002 Tahoe that was working 100% but this one is a different ballgame... I knew, or at least assumed, that there were a few things that needed attention when I bought it but it was a bit more than I expected...

Things not working:
  • Instrument cluster: The 4 gauges to the right in instrument cluster works fine occasionally. Did a refresh on solders on a handfull of resistors in the instrument cluster but I'm not sure it helped at all. At least one solder was bad. Battery symbol top right is always illuminated. Tach and speedo works fine. Background light intermittent.
  • 4WD, hi/lo panel: Works every now and then but usually dead (buttons don't work and LEDs dead).
  • Window motors: Works on rear doors from local panel but not on front doors. Passenger door window have a few mm movement occasionally.
  • Central locking: Might work from passenger door but not from drivers door or when using key or remote.
  • Radio: Never got any sound but display come and go randomly.
  • Airbag: Warning light on. Message in mirror: "Passenger airbag off" regardless of seat occupied or not.
  • Engine: Warning light on.
  • OBD-II: My (cheap) Bluetooth OBD dongle lights up but the app (Car Scanner, AndrOBD) cannot find any ECUs. I'm about to buy a "real" diagnose unit and hope for a Black Friday offer on UCAN-II-C Pro...
The car came with a lot of spare parts from another Tahoe but swapping parts is of no help.

Anyone with some hints on where to start looking?
 
Welcome to the Nation. We'll try and navigate through this basket case as best we can.

Anytime there are electrical gremlins, we recommend replacing the ignition switch. It can be the source of a lot of issues.

Next, you could try the Chevrosys app on your Android device with the Bluetooth dongle to scan all modules. However it is not available in the PlayStore, just APK downloads which can carry some risks (I've never had an issue with it). Car Gauge Pro does too but is no longer free. @TJBaker57 has ways to do scans using Terminal apps, which I will defer to him to explain. It might be worth it to get a better scanner, like a Launch or Topdon, or a Tech 2 if you can find one cheap (the prices have gone up on the clones from China)

I'm thinking for the windows, and maybe other issues, there might be a problem with the door modules and causing communication problems on the network with the modules, which can happen. After a full scan, you'll see which modules are responding and if you have a U code indicating a communication problem.
 
SveinHa said:
OBD-II: My (cheap) Bluetooth OBD dongle lights up but the app (Car Scanner, AndrOBD) cannot find any ECUs.
Click to expand...


Can you tell us specifically what OBDII adapter you have?

There are several different communications standards for OBDII. Not all adapters support all the standards.

To work with these old GM vehicles the device MUST support SAE J1850 VPW communications. Since that is a relatively old system some of the inexpensive OBDII adapters have dropped support for it.

There are adpters that do still support SAE J1850 VPW such as the models from Veepeak.
 
Thanks @Mooseman

I read somewhere that ignition switch may cause all sorts of trouble and I have a hunch that different gremlins appear each time I turn ignition on...

Working on a shopping list at RockAuto. Need parking brake wires also, that is the easy part...

Seems that my OBD dongle is bad, unable to connect to it today... It is a Dibotech Mini OBD-II to Bluetooth adapter. The label says: "Interface Supports all OBDII protocols"
 
The blue VeePeak is a fairly solid unit as @TJBaker57 suggested.
 
SveinHa said:
Seems that my OBD dongle is bad, unable to connect to it today... It is a Dibotech Mini OBD-II to Bluetooth adapter
Click to expand...

As Mosseman stated, the Veepeak Mini VP11 is a reliable unit proven to work with the older protocols..I own like 6 or so of these and they are less than $20.

One caveat of that device is that if one tries to use the same device with multiple phones, tablets and so on it requires re-pairing frequently. Like evey time you try to use a phone or tablet different than the last phone used. That can get annoying.

Veepeak has a couple more device models, the BLE and the BLE+ that do better when working with more than one phone or tablet. Naturally these models cost a bit more. I have several of these also.
 
I've opened and visually inspected the ignition switch. Looks fine and working well when measuring each switch with a multimeter but a new one will be ordered anyway.

Comments on the Youcanic UCAN-II-C Pro diagnostic unit? I want to have a unit which is fairly universal and to be able to correct the odometer (both instrument clusters I have show way too low odometer value, need to change it to official/correct value).
 
It looks good and seems to be able to do most of everything except I saw nothing regarding changing the odometer, just something about "Cluster Service Reset (mileage warnings)", which I think is for oil change reminders. There are no legal tools out there that can modify odometers.
 
Well, odometer modifying is illegal unless it is documented and reported to the authorities so it is obviously not an official selling point. I saw one review where the odometer was modified successfully on an Alfa 147 so I hope it will work for me... In my case it is about modifying it back to real value. I have the odometer value logged in official register every second year from day one so I know fairly well what value to put in.
 
I didn't say it was illegal as I'm in the same boat with my TB as it's showing 120k km more than original since I replaced mine as well. I said there are no legal tools available, at least not from the usual vendors. There are some available from places like AliExpress, like the DigiProg, but they are not perfect. Some will change the hexadecimal values in the background but the original values can still be pulled out, and sometimes will make the odometer not count up properly anymore. Even dealers can't change them except if it's a NEW cluster.
 
Welcome to GMT Nation... Checkout a Fellow Norwegian's Post who goes by the name of @Alfa-Norway ...
mrrsm

Thread 'How to Transfer Odometer Mileage Between IPCs on 99-02 GMT800 Trucks.'

It may not come down to actually having to Replace The Instrument Panel Cluster in my 2000 Chevrolet Silverado 1500 Truck… But I want to be prepared early, should this contingency become necessary. I've observed several Black Vertical Lines obscuring the Square Orange LCD Screen of the 'Message Center' on my IPC Console and decided to order a replacement... Just In Case. The information covered in the below listed Video indicates the Odometer (VFD) Vacuum Fluorescent Display Tube for the PRNDL & Odometer vs. the Orange LCD Panel apparently share some surface mounted components...

"10,000 Swedes... Ran Through the Weeds... CHASED by ONE Norwegian..." :>)
 
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Thanks @mrrsm I think the 99-02 is quite different compared to 03-. Today, the odometer is a quite secondary challenge and I believe it can be adjusted thru OBD-II. More important is to get the rest of the instrument cluster and the other stuff up and running.
 
Mooseman said:
you could try the Chevrosys app on your Android device with the Bluetooth dongle to scan all modules.
Click to expand...
I did install the Chevrosys app but it didn't communicate with my OBD dongle... Tried a few other apps and they communicate with the dongle but can't find the car...

Maybe I just order a UCAN right now. I did email Youcanic because they had a limited 10% off that didn't work and at the same time I asked about upcoming Black Friday. They didn't answer but within a couple of hours, the 10% off offer vanished and prices went up about 5%... so maybe I should look elsewhere...
 
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Amazon has tons of them and there will probably be Black Friday deals. I have a Launch CRP123x that I got for my 2021 Sierra and works quite well. I did have to pay an extra $25 subscription for some extra capabilities for it (IIRC for the electric parking brakes, which I didn't really need) but all scanning capabilities are there. It does scan all modules on it but I'm not certain if it would on the older vehicles, but I'm pretty sure it does. There are other brands like Topdon that's popular and, of course, Autel, which is the "Buick" of Chinese scanners with the price to match.
 
Since Youcanic don't seem to be in Black Friday mode, I ordered a UCAN unit. Estimated delivery on Tuesday (which probably means it crosses the Norwegian border on Tuesday and will be delivered to me earliest on Friday...).

It's a bit odd that my diagnostics don't find any modules. I guess that the first step is to follow wires and check connectors between OBD socket and BCM. That should be a foot or two of wiring so a fairly easy place to start.
 
You have probably already considered this issue in your Diagnostic Calculus ... But just in case not as yet... View the issues in THIS Thread that may have physical-mechanical solutions to this arcane problem of Rodent Infestations Occurring in Dormant Vehicles Causing Weird Electrical Gremlins:

mrrsm

Thread 'Under-Hood Vermin Infestation Issues'

An off shoot of the many problems that the COVID-19 Corona Virus Pandemic brought along is the fact that many of our vehicles… NOT just the GMT-360s and GMT-400-800 Vehicles have had to be parked for longer than ordinary time frames. For some of us, depending upon the region of the countries that we live in across North America, we have to be concerned about the insidious damage being done by… Rodents.

We’ve already have several Members attempting to solve ‘Weird PXXX OBD2 Trouble Code Clusters’ that devolved into discovering their Under-Hood Electrical Wiring Harnesses and...
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Good point @mrrsm but I have not seen ANY signs of such damage. This kind of damage happens but is not very common around here.
 
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The UCAN unit was delivered this afternoon. I hooked it up to me son's BMW 320d and cleared a few DTCs. Seems nice and have a lot of functions.

Hooked it up to my Tahoe and the VCI (OBD Bluetooth dongle) lit up. When I tried to read VIN and other data there was NO connection with anything... A general error message telling me the basic stuff like "Verify that the vehicle is OBDII compliant" and "Verify that the ignition is on" and so on...

I guess it is time to educate myself a bit on CanBus... and Tahoe CanBus wiring...
 
SveinHa said:
guess it is time to educate myself a bit on CanBus... and Tahoe CanBus wiring...
Click to expand...


Just remember that while the term "CanBus" is often used to describe every type of automotive network your vehicle does NOT use the 2 wire ISO 15765-4 Canbus protocol. Your vehicle uses the single wire class 2 serial data, SAE J1850 VPW.

A couple of resources:


www.csselectronics.com

OBD2 Explained - A Simple Intro [2025]

Learn all the OBD2 basics: What is OBD2? Is your car OBD2 compliant? What is an OBD2 PID? How do you log car data? And how do you decode OBD2? See our intro!
www.csselectronics.com www.csselectronics.com
 
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My FAVORITE Old School Classroom Auto Diagnostics Instructor...

 
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Measuring with a multimeter in the OBDII socket, I find around 1.7-2.2V with ignition off and 10V with ignition on. I have'nt come all the way thru the video yet but I can conclude that there is no short circuit on the bus but maybe one unit keeping the bus high for some reason. I guess that the next step is to unplug one unit after another and see if I get voltages around 7V. Time to find my oscilloscope...
 
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While the Splice Pack Design and Location may be different on the Full Size Trucks...the Basic Principles for Class 2 Network FUBAR Module to Splice Pack--> (s) Diagnostics (with or without a Handy Oscilloscope) are BEST Viewed via Will Robinson's Eponymous Training Video Below... It simply does NOT get any Better than THIS!


For a LOT More on Oscilloscopes...

mrrsm

Thread 'How To Use PICO #2204A & HANTEK #1008C Oscilloscopes'

You don't need a Huge Bag of Coins in order to obtain and use an Oscilloscope for performing In-Depth Wave Form Analysis in Automotive Applications on everything from Problematic Electronic Fuel Injection to obtaining accurate Compression Tests to Diagnose Internal Engine Conditions.

HANTEK makes (...and Amazon, eBay and OTHER Outlets sells) ALL of the discreet equipment components necessary to accurately conduct these types of Automotive Diagnostics ... and all can obtained on a Very Modest Budget.

The Basic Oscilloscope Hardware is listed below:

(1) Windows or surprisingly... a...
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I think I found the star-point but it is absolutely inaccessible with more than a half hand...
PXL_20251120_213248272.jpg

It doesn't look exactly as in the video but I think it's the one...
 
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:thumbsup: Bingo!
 
If it has Steel Teeth when you disconnect it...You can test the Female Side right there... Not a very comfortable location... but with Printed Splice Pack Wiring Diagrams at hand...Testing and Elimination with the Oscilloscope should be very straightforward.

More Data...

2002 Yukon XL splice pack 205 location?

Where is it? Can't find it. It's not where the shop manual diagram says it is (page 8-319 of volume 4). It's not where the shop manual table of wiring systems says it is (page 8-164 of volume 4). It's not where posts on other forums says it is (e.g. "to the right of the DLC" (Data Link...
www.tahoeyukonforum.com www.tahoeyukonforum.com

splice pack 205.JPEGsplice-pack-205-l.jpg
 
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I have the diagram (missing a few lines in this screenshot):
SP205.png
It's late, I'll continue tomorrow...
 
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SveinHa said:
I find around 1.7-2.2V with ignition off and 10V with ignition on
Click to expand...


FWIW, regarding that 10 volt reading, I have never seen a voltage that high on a class 2 data bus. Not with a multimeter. The most I usually see is maybe a brief 2 or 3 volts while I cause a high rate of traffic on the data bus. And even then I only see that when I video the multimeter so I can catch the particular fraction of a second it happens. Something sounds quite wrong there on yours.

Since the voltages appear normal with key off I might suspect a module whose operating power is switched through the ignition switch and thus is not capable of operating with key OFF.

Normally a number of modules can be communicated with while the key is off, however, that requires manual communications using a serial terminal as most all apps and scantools require ECM/PCM to be active which is generally not possible with key OFF.

As an example here below I just connected to my 2005 Yukon out in the driveway while I stay warm and dry in the house. Of course there is no key in the vehicle. I set the message header to address my messages to the TCCM and turn on spaces between bytes. I then 'pinged' the TCCM twice. The first time gets a "NO DATA" message from the OBDII dongle as the TCCM was asleep. The second ping got the expected response from the TCCM, the first ping having awakened the TCCM.
I then requested the status of all possible DTCs from the TCCM. The block of 13 responses tells me the status of all the DTCs.

Screenshot_20251120-192129_Serial Bluetooth Terminal.jpg
 
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Now, I've spent hours getting the cam out of SP205 and measuring a bit. Access is so bad that I gave up when finding pin H, circuit no 2218, Serial Communications Circuit fed the bus with 10-12V. In my documentation, there is no reference to 2218...
 
I found some really low resolution diagrams and by a bit of guesswork it seems that circuit no 2218 goes to SP206:
SP206.png
Haven't found it yet...
 
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Found it in left B-pillar. Pin B feeds >10v
 
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So far, I left the "comb" out of SP206 and the rest of the car started working again. No sound in the radio/CD but I guess that may also have to do with SP206 since the Bose amp is located under the drivers seat.

SP206, pin B is circuit no 1128 and I haven't found out what that is.

For now, I just leave the "comb" out of SP206 and go on with other tasks to get the car road legal. A few parts are on its way from RockAuto...

Thank you all for your help so far. I couldn't have come this far without it :2thumbsup:
 
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CRC Electric Solvent... BFF for the Clean Up of those areas and Connectors:



1763906529700.png

...and when it comes to GROUNDS.... On Full Size GM & GMC Trucks...


Fun Fact:

After Cleaning Up the Ground Connections... using a Dollop of Dielectric Grease prevents Dissimilar Metal Corrosion (AKA Galvanic Corrosion) that ALWAYS Happens...No Matter WHAT ...because they ACT LIKE LITTLE BATTERIES.
 
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