I suspect BCM... thoughts?

[TrybalRage]

Have you tested the alternator beside just checking the voltage output with a multimeter? If it's not properly charging the battery, that would explain just about everything.

I have not. To be honest I've never tested an alternator any other way. I know autozone and such offer an alternator test, what's different about it?

When running, it's over 14v, on multimeter and on gauge. If I go for a drive, come home, shut off vehicle, pop hood, battery tests at 12.7-12.8.

 

[intheburbs]

I have not. To be honest I've never tested an alternator any other way. I know autozone and such offer an alternator test, what's different about it?

When running, it's over 14v, on multimeter and on gauge. If I go for a drive, come home, shut off vehicle, pop hood, battery tests at 12.7-12.8.

I believe it's a load test. Volts don't matter if the amps aren't there. Again, if for whatever reason the alternator is bad, that explains just about everything. Simplest explanation is usually the correct explanation.

 

[Doubeleive]

I believe it's a load test. Volts don't matter if the amps aren't there. Again, if for whatever reason the alternator is bad, that explains just about everything. Simplest explanation is usually the correct explanation.

easy to find out just turn everything on headlights, wipers, defroster, heater blower, seat heater, radio, windows up/down, adjust seat back n forth and turn the key to run only to test battery

 

[TrybalRage]

easy to find out just turn everything on headlights, wipers, defroster, heater blower, seat heater, radio, windows up/down, adjust seat back n forth and turn the key to run only to test battery

But how would that load test the alternator? If the battery is fully charged (like I have it on a charger right now) it would be fine, and if it were already low it would just test lower?

 

[Fless]

Have you tested the alternator beside just checking the voltage output with a multimeter? If it's not properly charging the battery, that would explain just about everything.

^^ This. In addition to the voltage test it should be checked for how much current it's generating. Wonder if the RVC is working correctly?

Also a thorough check and cleaning of the battery cables and main grounds should be done, if it hasn't yet.

 

[TrybalRage]

^^ This. In addition to the voltage test it should be checked for how much current it's generating. Wonder if the RVC is working correctly?

Also a thorough check and cleaning of the battery cables and main grounds should be done, if it hasn't yet.

Yes, cables are clean, new main ground wire and an additional 4ga wire from the block to the firewall was added.

Guess I'll run it up to autozone tomorrow.

But I gotta be honest, a battery above 12v and causing the whole system to bug out seems... like more than just a low battery.

 

[Doubeleive]

But how would that load test the alternator? If the battery is fully charged (like I have it on a charger right now) it would be fine, and if it were already low it would just test lower?

you would see a heavy drop in voltage

 

[gpracer1]

There is more to testing an alternator than just volts and amps. They test to make sure the rectifiers are not bad, or you will have AC ripple which can cause havoc with data transferred between canbus modules.

 

[Geotrash]

There is more to testing an alternator than just volts and amps. They test to make sure the rectifiers are not bad, or you will have AC ripple which can cause havoc with data transferred between canbus modules.

^^^This.

I'm with the others here that the alternator is suspect at this point. And Autozone doesn't have any credibility with me when it comes to testing them in the car. The only way to do it right is with a bench test. At that point, you might as well just replace the thing. I've been running one of these in both of my trucks for a few years now, and no problems at all:

https://www.amazon.com/gp/product/B00SL6T29K/ref=ppx_yo_dt_b_search_asin_image?ie=UTF8&psc=1

 

[donjetman]

^^^This.

I'm with the others here that the alternator is suspect at this point. And Autozone doesn't have any credibility with me when it comes to testing them in the car. The only way to do it right is with a bench test. At that point, you might as well just replace the thing. I've been running one of these in both of my trucks for a few years now, and no problems at all:

https://www.amazon.com/gp/product/B00SL6T29K/ref=ppx_yo_dt_b_search_asin_image?ie=UTF8&psc=1

Me too, almost 4 yrs and 40k miles ago. No problem. $101 back then.

 

[TrybalRage]

Alright fellas, new alternator on it's way. While I wait, I've pulled the main fuse box to check for corrosion (nope) and started pulling connectors on other modules to check them as well. Going to put a light coat of dielectric grease on them just for peace of mind, following this tsb.

I am a little concerned about a few codes that popped, still. The seat control going to ground (which according to alldata could also be just low voltage).
The fact that I cannot connect to the amp (is it disconnected? Malfunctioning? Replaced but never coded? Is the amp coded in these?) even when fully charged up.
Checked high and low for any type of fleet tracking device per alldata. Looking for corroded/rubbed wire while I'm at it.

 

[TrybalRage]

New alternator should be here any time now (thanks Amazon!). As I said, while I'm waiting I've been inspecting/dielectric greasing all the connectors mentioned in that TSB. I found something that looks... suspicious.

The first item mentioned is a metal wire clip on the transmission. Lo and behold, my plastic split loom is crumbling at that location. I pull it apart and I'm seeing... marks? On the high speed wiring.

My wires:

https://imgur.com/rZvHDuG

It looks awfully similar to the types of marks pointed out in another portion of the TSB.

I guess the question is... do we have a small short happening here?

I don't see exposed copper, so I don't think I need to cut/splice anything here, right? Just wrap it up better to protect it?

 

[Jimmyy]

I would wrap it. It's a twisted pair like network wire. Maybe some brush on liquid tape then wrap the bundle.

 

[Fless]

What does the TSB say to do if those marks are found?

 

[Rocket Man]

New alternator should be here any time now (thanks Amazon!). As I said, while I'm waiting I've been inspecting/dielectric greasing all the connectors mentioned in that TSB. I found something that looks... suspicious.

The first item mentioned is a metal wire clip on the transmission. Lo and behold, my plastic split loom is crumbling at that location. I pull it apart and I'm seeing... marks? On the high speed wiring.

My wires:

https://imgur.com/rZvHDuG

It looks awfully similar to the types of marks pointed out in another portion of the TSB.

View attachment 379708


I guess the question is... do we have a small short happening here?

I don't see exposed copper, so I don't think I need to cut/splice anything here, right? Just wrap it up better to protect it?

Yours doesn’t look like the insulation is open like that TSB picture so I say just wrap it up better and put some new split loom on it. I don’t think there’s a problem there.

 

[TrybalRage]

What does the TSB say to do if those marks are found?

It just says "repair wire as needed" and references the manual. The manual only has instructions for exposed copper, so I guess I'll just wrap it up.

 

[TrybalRage]

Yours doesn’t look like the insulation is open like that TSB picture so I say just wrap it up better and put some new split loom on it. I don’t think there’s a problem there.

They do catch a fingernail so it's like a slight indentation, but I don't see exposed copper there.

 

[petethepug]

It looks like GM caught that their employees were yanking the harnesses through the plugs and firewalls so hard it creased the insulation and left residual metal behind from the unpainted pathways.

Typically this is where a wire would be stretched and give a lifetime of grief when heat cycles raise and lowers the conductivity. This doesn’t look stretched, just bruised.

Can you make a list of everything you’ve replaced to date? Ten pages came up quickly and others chimed in with similar issues remedied on their truck.

 

[TrybalRage]

Battery, alternator, and BCM have been replaced to date.

Wire harness repaired where it was damaged at the three-way split on the top of the intake manifold (separate thread, separate problem, evap issue, now resolved).

I have been going through all of the electrical connectors and checking for corrosion per the TSB previously mentioned, and lightly coating them with dielectric grease as I go just for good measure. No corrosion found.

Today, I was sitting with my tech2 and I'm getting repeating errors for a drivers seat memory module shorting to ground (B3920 code 2). I'm also getting an error powering VCIM/Onstar issue that won't go away.

For the memory seat module, alldata gives this guide to check:

B3920 01 or B3920 02
1. Ignition OFF, disconnect the X1 harness connector at the MSM.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuits listed below and ground:

* Front vertical motor terminal 12
* Front vertical motor terminal 13
* Rear vertical motor terminal 15
* Rear vertical motor terminal 16
* Seat horizontal motor terminal 9
* Seat horizontal motor terminal 10

♦ If the test lamp illuminates, test the control circuit for a short to voltage.

3. Test for infinite resistance between the control circuits listed below and ground:

* Front vertical motor terminal 12
* Front vertical motor terminal 13
* Rear vertical motor terminal 15
* Rear vertical motor terminal 16
* Seat horizontal motor terminal 9
* Seat horizontal motor terminal 10

♦ If not the specified value, test the control circuit for a short to ground.

4. Ignition OFF, disconnect the X4 harness connector at the MSM.
5. Ignition ON, verify that a test lamp does not illuminate between the control circuits listed below and ground:

* Lumbar horizontal motor terminal 12
* Lumbar horizontal motor terminal 13
* Seat recline motor terminal 15
* Seat recline motor terminal 16
* Adjustable pedal actuator terminal 9
* Adjustable pedal actuator terminal 10

♦ If the test lamp illuminates, test the control circuit for a short to voltage.

6. Test for infinite resistance between the control circuits listed below and ground:

* Lumbar horizontal motor terminal 12
* Lumbar horizontal motor terminal 13
* Seat recline motor terminal 15
* Seat recline motor terminal 16
* Adjustable pedal actuator terminal 9
* Adjustable pedal actuator terminal 10

♦ If not the specified value, test the control circuit for a short to ground.

7. If all circuits test normal, replace the MSM.

I am not getting any illumination on my test light, nor are the circuits grounding out. So new MSM time?

 

[petethepug]

Thanks Man!

At the end of this year GM is yanking all of our 2G (07-14) OnStar / VCIM connectivity. Until I can see if I can get a 3G (15-20) working in our Gen, diagnosing it is moot. It’s likely the antenna that’s taken a dump from water intrusion. The OnStar modules themselves don’t usually die. They are killed by its internal (one time) battery dying from key left on in accessory position and battery disconnected.

The seat can be tricky. ISS automotive has refurb parts for the switching assemblies if that the fault. The gearing can also deteriorate and cause the motors to self destruct. The fix is to find a replacement and swap your seat guts into it.

Depending on your M/Y you may have a MSM close to a place rain falls on it through an open window.