Relearn BCM

Richard Bernard · January 5, 2020

Hello everyone, new to the site. I have an issue where I keep on getting rear access open and I believe that I have faulty BCM. there are other telltale signs like shaking at high speeds and the clock on my radio not keeping time. The question is, can I get a used BCM and have my '10 Denali relearn it or do I need to have my BCM reprogrammed? Thanks for any info!

davester · January 6, 2020

I would suggest that a faulty bcm is WAY down the list of what's causing that problem. Have you electrically tested both the switch, the wiring and all the connectors for that circuit?

Richard Bernard · January 6, 2020

I have not. With there being more issues that are BCM related, makes me believe that it's the BCM.

davester · January 6, 2020

The bcm also likes good power and ground, and not having them can cause a variety of problems. And for my truck (previous generation from yours), there are multiple power & ground connections to it, and if one isn't right, it can cause multiple systems that appear unrelated to not work right.

You can throw a fairly expensive part at your truck and hope it fixes the problem, or you can figure out the what the problem is and fix that (and it may turn out to be the bcm).

And you'll want to get the bcm programmed by the dealer, as while it's a semi-generic part (as in, shared by variety of vehicles), it is programmed for the specific options installed in your truck. Just putting in another bcm with the same part number may not function correctly.

Electrical problems generally suck to figure out for most people.

Some things that help with figuring them out:

-full service manual. online subscription isn't that expensive, and it has the wiring diagrams for your vehicle, as well as the diagnostic procedures to fix pretty much any problem your truck has

-a good electrical tester, such as an Autel PowerScan PS100. It's simple to use one-handed, can tell you if a connection is connected to power or ground, and provide power or ground for testing purposes, and more. I find it much handier to use compared with using a multimeter with 2 probes.

-I think a techii can still be used with your truck (but you may want to verify this). knockoffs aren't expensive, and posts I've seen say most people find they work well. they talk to all the computers in your truck, get all the codes from them, and also can perform a bunch of testing and diagnostic procedures from the full-service manual

davester · January 6, 2020

Just as an example, in my truck, the rear defog wasn't working. Button on the controller would turn on (IIRC, but I'm not sure now), but no voltage at the window. Fuse was good, was suggested to replace the controller, but I looked through my full-service manual's wiring diagram, found the circuit went through a relay, did a quick check by swapping relays, still didn't work, then probed the contacts for the relay, and found that the "controller" side of the relay wasn't getting 12V when the button was pushed. Traced that wire on the wiring diagram, and found that it went through another fuse (one of the fuses for the bcm) had blown. Replaced that fuse, and it worked again.

swathdiver · January 6, 2020

8 hours ago, Richard Bernard said:

Hello everyone, new to the site. I have an issue where I keep on getting rear access open and I believe that I have faulty BCM. there are other telltale signs like shaking at high speeds and the clock on my radio not keeping time. The question is, can I get a used BCM and have my '10 Denali relearn it or do I need to have my BCM reprogrammed? Thanks for any info!

You would have to have the new or used BCM programmed to your VIN. If you like the Denali and plan to keep it, get yourself a Tech-2. Then you stop guessing and start knowin' what's wrong with your truck. It will likely pay for itself in just this instance.

Doug_Scott · January 6, 2020

I doubt the vibration at high speed is related to the BCM. I would do as what was already suggested. A poor connection on the battery can reset your clock to 12:00 if the connection causes low voltage during cranking. There is likely a switch somewhere around the rear door causing the error you are seeing. Back in the old days they used a very simple pillar switch that controlled the ground to dome lights and door ajar warnings. Doubt they left it so simple though.

Richard Bernard · January 6, 2020

11 hours ago, swathdiver said:

You would have to have the new or used BCM programmed to your VIN. If you like the Denali and plan to keep it, get yourself a Tech-2. Then you stop guessing and start knowin' what's wrong with your truck. It will likely pay for itself in just this instance.

I will take your and @davester advice and get a Tech-2 (and a powerscan as well).

I'll check the grounds again (as I believe I checked them all) and will feel really stupid if it comes down to a loose ground.

Richard Bernard · January 6, 2020

4 hours ago, Doug_Scott said:

I doubt the vibration at high speed is related to the BCM. I would do as what was already suggested. A poor connection on the battery can reset your clock to 12:00 if the connection causes low voltage during cranking. There is likely a switch somewhere around the rear door causing the error you are seeing. Back in the old days they used a very simple pillar switch that controlled the ground to dome lights and door ajar warnings. Doubt they left it so simple though.

Some of the research I have done has stated that a bad BCM could lead to high speed shaking. The tires are balanced and all. So if it isn't the BCM then I have another issue.

The clock doesn't reset, it will be stuck at a certain time and then jump to the correct time.

The switch in the back seems fine. The only other thing I need to try (again and the right way) is disconnecting the cables to the battery and trying a hard rest.

Richard Bernard · January 6, 2020

11 hours ago, davester said:

The bcm also likes good power and ground, and not having them can cause a variety of...

Thanks for this info. I do appreciate it.

Richard Bernard · January 12, 2020

Well I'm probably going to be the laughingstock of this forum here. Besides the BCM issue that I thought I was having, I needed to replace my sway bar stabilizers. One was missing and the other one was broke from the bottom a arm. So did what I had to do to get my sway bar back in its original position and put on two brand-new stabilizers. And what would you know, no more electrical problem or "rear access open" issue. My mind is blown!

riverbanks · January 12, 2020

Changed the frequency of the vibration?it will come back eventually,but when

Richard Bernard · January 13, 2020

6 hours ago, riverbanks said:

Changed the frequency of the vibration?it will come back eventually,but when

Sometimes it was happening while I was just sitting at a stop sign. Maybe when the sway bar was in the wrong position it was hitting something?

riverbanks · January 13, 2020

No idea,but,think about it,any new problems from someone else,about anything,change the sway bar bushings,out,lol

Doug_Scott · January 13, 2020

10 hours ago, Richard Bernard said:

Sometimes it was happening while I was just sitting at a stop sign. Maybe when the sway bar was in the wrong position it was hitting something?

I would think that if the swaybar was touching something you may hear a "hum" type noise, not feel a vibration at idle when not rolling.