Is it possible for the BCM to work intermittently or is it more or less "good" or "no good"? I've narrowed down my column lock problem to possibly being the BCM. When everything is working, when I pull the key from the ignition when I shut the car off, the doors unlock, the CLB clicks then the BCM clicks. At times, out of no where, When I pull the key, the doors unlock, the BCM clicks, then the doors unlock again...no CLB click. Once this happens, I get the "service column lock" message and I'm stranded for any length of time. I've checked for every possible short or poor connection and even disassembled the BCM and it's perfectly clean (no corrosion). So is it possible that something in the BCM is going bad? I always thought that the BCM would either work or it wouldn't? Any input is appreciated. Thaks!

 

Have you displayed DTC codes on the DIC ?? If the BCM is failing you should have either a B0605 (failure of the non-volatile EEPROM memory) or a B1000 (failure of the BCM processor).

 

All that the B0605 and B1000 codes tell you is the BCM knows that something has gone wrong inside it's core. Those codes tell nothing about, or will be set by failures of the perihelial IO components. If you get those then your BCM is probably bad, but there is a LOT of other things that can go wrong with the BCM that won't set those codes.

To answer the question, Yes, it is possible and very likely for the BCM to work intermittently. There is a lot of components both electronic and mechanical (relays) that can fail intermittently.

Sounds like it may be a bad relay in the CLB or a bad relay in the BCM that controls the column lock may be bad. It would be fairly easy to check with a voltmeter. What codes are getting set?

 

I have 2 CLBs and they both work and don't work when ever the system is acting up...so I ruled the CLB out. As far as codes, I have several history codes which are all communication loss codes. But the BCM codes are B2587 H and B2592 H...column locl/unlock drive (A) and column lock/unlock drive (B). What that means, I'm not sure. I'm assuming it just tells that the lock/unlock state was not correct from when the system acted up. Maybe it does have something to do with my problem?? Also, would the ignition cylinder have anything that could possibly be causing this or is it totally isolated from tripping the column lock message? Thanks.

 

The very first thing that you need to do is check your 12 VDC battery. If it is low or defective, it can cause column lock issues and BCM issues. Take it to Auto Zone and have them test it. While it is out, clean the battery cable terminals.

My BCM had corrosion on the back of the board from the passengers foot well leak.




Bad BCMs can cause some weird SH*$

I cleaned it off and it worked good again until I accidently chorted the BCM to the HVAC fan motor!

BC

 

Thanks! I will definitely test the battery. Also, even though the BCM panel looks perfectly clean and fine, do you think it's possible that corrosion still may exist? Thanks again!!

 

I would switch out the Hvac relay for the CL relay and see if the problem is still there or if you start to have blower motor problems.

 

Do these codes reappear after being cleared? Or did they only show up once after fuse #23 was found blown? A blown fuse #23 will cause both of these codes to be set.

Also, clear all your codes and see if you have any of the U codes reappear.

 

I believe the codes appeared after the fuse was blown. I clear them and they don't immediately come back. One time it acted up and no codes were set.

 

Yes, BCMs can act intermittantly good and bad.

My 01 suddenly got a no-start problem. This is because my BCM doesn't come out of sleep mode, after the car sits for 15 minutes (The BCM is supposed to tell the other computer boxes to go into low power shutdown, 15 minutes after the car is shut-off, if no activity is detected, and then itself go into sleep mode). I can only start it if I remove and reinsert the BCM 12V Logic power feed fuse #25.

I had the BCM apart on my bench for a few days, then reinstalled it in the car. The problem went away for a week, but has now returned. I verified that the fault is indeed inside the BCM, not some external wiring or circuits.

I suspect that there is a hairline crack in one of the solder joints of the PC board. I will remove it again, and resolder al the joints.

Your problem sounds like one of the two relays inside the BCM (or the relay drive circuits) is intermittent. Try resoldering the relays, they are the two black plastic cubes in the lower right corner of the board. There is one more relay, external to the BCM which could be the problem. It is the Colum Lock Power Relay mounted above the BCM. This external relay provides 12V power to the BCM internal relays. The internal BCM relays determine the polarity of the Colum Lock Drive signal : One polarity for lock, the opposite for unlock.

 

Thanks!!! I'll give that a shot too!!

 

The column lock relay above the BCM...are you referring to the recall modification realy added by GM, or a different one?

 

There is a colum lock relay there from the factory, prior to any GM recall mods. I believe that is true for all year C5s.

 

Still trying to get a total understanding on my problem. As I mentioned above, when I remove the key, the doors unlock, the CLB clicks and then the BCM clicks...when it's working. A couple days ago it stopped working again. The next day, it was fine again. Now, this time, when it started working...the doors unlock and the BCM had two clicks, BUT it was working. NO CLB clicks???? It's just odd that it will work even when it's doing different things. Does anyone know, or can they please listen to their car? When you shut if off and remove the key, just listen for the sequence of events. Hopefully that can help me determine at least which are the correct sounds, so I'll know which state is the absolute correct one. I have a new BCM on the way and today I'm having the battery checked. I just don't see how the battery could affect it for 50 start cycles though, then work fine for a period of weeks. Sounds more like something more in depth. But I guess one never knows. Thanks for any help.

 

Just got back from AutoZone...they have my battery now doing a deep chare on it. The test showed it was good, but low charge. I was explaining the problem to the manager and he said that when the doors unlock like they do when it's bad, he said that is sign of the battery not having enough power to run the computers? So maybe that's a symptom to my problem. I'm off to pick up the battery. I'll keep you posted.

 

What type of battery do you have?? It charging the battery solves the problem temporarily, and then the problem reappears, the battery could have an internal short and loose its charge just sitting in the car over a period of time. You can get a volt meter and read the terminal voltage. If the battery voltage drops down below 11.5 VDC, you might have a battery issue.

Bill

 

It has a Delco battery. I just picked it up and I put a volt meter on it and it reads 12.50v. Before I took it there today it read 11.9v...but it was also working?? I'm going to drive it and hope it keeps working. That's the scary part...I never know when it will bite me. Thanks Bill.

 

BTW Bill, would you mind PM me a phone number so that I could explain better?? Thanks

 

The real test is: What is the voltage when you first crank it in the morning and how far does it drop down during the cranking process??? I had a OEM Delco in my 98. It was 5 years old and still cranked the car just fine. I also would get tons of U series codes (all history) and lots of lost communications messages. Another symptom that I had was; I would frequently loose SYNC on my fobs. Come to find out, my OEM battery was dropping down to 9 VDC during the first few milliseconds of the cranking process when the starter draws the most current. During that low voltage the modules would shut down until the voltage got back up above the cut off threshold. Once the car started, everything worked fine.
You have a PM!

Bill C