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sprinkles08
sprinkles08, ASE Certified Technician
Category: GMC
Satisfied Customers: 21570
Experience:  ASE Master and Advanced level certified. Factory trained with 15 years dealership experience
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Temp, fuel, Trans temp, tow/haul, autolock when put in gear,

Customer Question

Temp, fuel, Trans temp, tow/haul, autolock when put in gear, DIC all not working. Batt warning flashing but new alt and batt are in. All warning lights flashing in msg center. Airbag light on. PRNDL lit but no indicator present. This began happening occasionally, then guages would work upon startup but quickly die, then would only work if key on but not running, now totally dead.
Submitted: 9 months ago.
Category: GMC
Expert:  Gary replied 9 months ago.

do you have any access to a scan tool to see live data ?

do you have a multi meter on hand ?what does work in the dash cluster ?

Customer: replied 9 months ago.
Scan tools read "communication error".
Tach, speedo, volt, & oil temp are only guages working. Lights in cluster work. Message center flashing battery, low fuel, security. Prnd321 showing and lit, but no gear select indicator.
Yes, I have a multimeter.
Expert:  Gary replied 9 months ago.

communication error trying to read which module ?

Customer: replied 9 months ago.
All. I can hook it back up tonight and tell you exact run down of errors, in order, if needed. Scanner can't communicate with any module. I've tried 3 scanners.
Expert:  Gary replied 9 months ago.

can you see if terminal 16 is 12 volts at the ALDL connector with the ignition key ON

Customer: replied 9 months ago.
What/where is ALDL connector?
Expert:  Gary replied 9 months ago.

that is where the scan tool is plugged in

Customer: replied 9 months ago.
I will check after work.
Expert:  Gary replied 9 months ago.

ok let me know

Customer: replied 9 months ago.
12.49 volts it's reading.
Expert:  Gary replied 9 months ago.

and no communication with any module at all ?

Customer: replied 9 months ago.
None.
Customer: replied 9 months ago.
In fact it says cannot communicate.
Expert:  Gary replied 9 months ago.

if it has the power there it should communicate

not even a basic code reader will read ?

can a Pep Boys or Auto Zone communicate with it ?

Customer: replied 9 months ago.
No they can't, that's the first place I tried. They are getting the power from connector to run the device, but it won't communicate. I also have a buddy with an expensive one; same thing happened.
Expert:  sprinkles08 replied 9 months ago.

Hello and welcome to JustAnswer!

If communication with no module is possible then you have a bus communication issue, and that's going to be why you're seeing the cluster act this way. It isn't receiving information from various modules because it can't communicate with them.

It's going to take some in depth testing to determine what is going on. The modules all communicate over a wired network. When the network shorts to power or ground either due to a wiring issue or internal failure in a module it will prevent communication.

If the bus is shorted to voltage then you can try removing fuses to see when communication returns and then concentrate on any modules on that circuit. IF it's shorted to ground, or if removing fuses doesn't change anything, then modules can be unplugged one at a time to see if communication returns.

If a short to power ro ground is still present with all modules disconnected then the problem is somewhere in the harness.

Customer: replied 9 months ago.
from what I understand, I need to hook up diagnostic tool to OBD connector, and begin by pulling a fuse, then replace, then on to the next fuse, and so on? All fuses in both boxes?
Expert:  sprinkles08 replied 9 months ago.

Yes, you can connect a scan tool and pull fuses, each time checking for communication. If removing a certain fuse brings back communication then the problem is either an internal failure in a module on that circuit, or there is a short between the powered circuit and the communication bus in the harness.

Customer: replied 9 months ago.
When you say module, are you referring to something such as power windows, a/c, etc? Or a vital engine function?
Expert:  sprinkles08 replied 9 months ago.

A module is an electronic control unit that controls a system such as the ECM, TCM, airbag and ABS module, instrument cluster, radio, amp, etc.

Customer: replied 9 months ago.
Just learned that at one point, this truck had been rained in while sunroof was left open overnight. Carpet was wet for months, to the point there was mildew. This was a couple years ago, and vehicle ran at least a thousand miles afterward. Does this help you? I will have time tomorrow to test as you instructed earlier.
Customer: replied 9 months ago.
I meant it ran without electrical problems. Vehicle also had aftermarket radio, and operated fine. Removed radio, still ran fine.
The guages, at one point, would operate with key in acc position, but would cease to operate shortly after start up. Then, a week or so later, would operate on acc position maybe 1 out of 5 times, as in I could turn key on off on off on and gauge would work momentarilly.
Hope this helps. I will r/r fuses tomorrow.
Thank you, BTW
Expert:  sprinkles08 replied 9 months ago.

It's possible that a module has failed from the water intrusion.

Customer: replied 9 months ago.
Now my scanner is not even saying no comm. Have to wait until my buddy who owns it can come try it on his own car and reset scanner if necessary. Sorry for the delay.
Expert:  sprinkles08 replied 9 months ago.

Not a problem.

Customer: replied 9 months ago.
I will not have chance to work on again until this weekend. Will I still be able to communicate with you? How long does my access last?
Expert:  sprinkles08 replied 9 months ago.

YOu can reply here at any time.

Customer: replied 9 months ago.
Don't know if this helps, but guages will work if I turn on acc position and wait about 30 sec...also, occasionally, when I give it decent throttle off the line, when it shifts into second, the engine cuts out for a fraction of a second. Just enough to make front end dive, and throw me towards the dash. But it's very quick, and only from 1st to 2nd. And doesn't happen often.
Customer: replied 9 months ago.
Oh, and soon after I start truck, when I've gotten guages to work as mentioned above, they die again. I hope some of this helps.
Expert:  sprinkles08 replied 9 months ago.

Turning the key to accessory before starting the engine works every time?

Customer: replied 9 months ago.
Not reliably. It varies in period of time it takes for them to activate. But, as I said, they die again soon after startup. Also, the "trip computer" (DIC?) works consistently while on acc. Even updates miles til empty when guages activate.
Expert:  sprinkles08 replied 9 months ago.

It may be coincidence but it may also be acting that way because the culprit circuit or component isn't being powered in the accessory position but is in run.

Customer: replied 9 months ago.
Just an update to keep you informed, in hopes that you'll be able to better diagnose. My door locks now have a mind of their own. After I lock truck with remote, the locks are occasionally unlocking. I got in and listened, and they do it sporadically. I'm wondering if the anti-theft system, which warning light it on for anyway, could be an issue, but I see no alarm fuse labelled in either box. Is there a fuse for that system?
Expert:  sprinkles08 replied 9 months ago.

Do you have a key fob? If so have you removed it's battery or removed the fob from the vehicle area to see if the locks stopped?

Customer: replied 9 months ago.
I didn't because the alarm is what notified me of locks unlocking. If it were key fob, then alarm would be disabled upon unlock, right? It seems that whatever this Guage issue is, it's related to the DIC as well. I am probably wrong, but it seems there must be a computer issue at hand here. As stated in opening question, there are several features that all went out at same time. I've looked at grounds. I've cleaned connectors. Replaced fuses that were bad. Wiggled every wire loom I can find under hood, and also under dash and center console when I removed them. In my limited experience this can usually trace a bad wire, or at least identify location. Is there any computer that controls all these functions? Btw, rear air doesn't work either. Not sure if it ever did. I'm sorry to overload with info, I'm just trying to be as thorough as possible and document everything for you.
Expert:  sprinkles08 replied 9 months ago.

Can you explain what you mean by the alarm is alerting you that the doors are unlocking?

Customer: replied 9 months ago.
The alarm goes off because doors are unlocking themselves. As if someone were to push unlock button thru open window while car is locked. I get out, hit lock on remote, and a while later alarm goes off.
Expert:  sprinkles08 replied 9 months ago.

The alarm wouldn't go off because a door is unlocked, it would go off if a door ajar switch closed while the system was armed. You may have a BCM issue but it could also be wiring or an ajar switch.

Customer: replied 9 months ago.
these could possibly affect the guages, DIC, tow/haul, PRND321 indicator, Trans hard shift, etc? Which is more likely and should I investigate first?
Expert:  sprinkles08 replied 9 months ago.

The BCM or any other module could be causing the bus problem.

You may have any combination of a number of different problems happening at the same time, there may be a handful of unrelated problems. The bus issue needs to be dealt with first.

Customer: replied 9 months ago.
Just to clarify...I need to get the OBD connector working, and use the method you described a few days ago. That's first, formost, and will be most practical.
Customer: replied 9 months ago.
do I pull those mega fuses one by one too when I'm doing this?

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