Hello,
Ive been having intermitant BCM problems, where all my gauges on my dashboard would go to zero and I would get the Messages "Power Steering" and "Low Fuel" while driving. Interceptors continue to operate and report data, such as Speed and RPM and Fuel Level. Anyways when I wuold stop the gauges and everything would start working. While the gauges were reading zero sometimes they would jump to 20mph and 2000 rpm and go back to zero with a dingding ding. The security light also illuminates, and intermitantly flashes the brake light.

Power locks/ power windows continue to operate as well as the AC. Don't know about my lights though because its been day time every time its happened. The Radio also continues to operate normally. This malfunction occruse when useing either key in the ignition. I have purchased a spare key a while back. I tried swaping the key out because it is the eaysest thing to change and i figured the key chip might have beem fried but it still freaks out occasionaly with the spare key too. Yes I had the spare key programed by the dealership when I baught it. Anyways when I stop the problem corrects itself, Speed stays 0 (Since im stoped) While RPM goes to 1000 and bounches a little due to 60# Injectors + Canned Tune. Ive posted about this malfunction before but figured id start a new post so that I dont get more funeral directior stat awards. haha

Anyways some one sugested the BCM. The Service Manual says to replace my gauge cluster, then change my BCM. I dont want to waste money throwing parts at it. Im thinking there is a communication loss between the PCM and the BCM. When looking at the schematics i came accross something called the "Vehical Communication Interface Module" What is it? What does it do, and where is it?


Also any other information would be helpful. The only code in my PCM is P0171 from my ZZP Canned tune. I dont know if my hand held scanner can read BCM codes. What would it cost for a dealership to pull BCM codes? Because I ahve the same scanner that Autozone and Advanced use.

Any Helpful information would be appricated, Thanks,

I HATE Intermitant problems. You can only troubleshoot them when the malfunction is occoring. If it fixes itself everythings going to check good. If I change something I wont know for a while if it corrected the problem or not. Intermitant should be a swear word

 

No need to make the same thread twice........

 

Mybad sorry, I originally posted it in the electronic section, then figured this would be a better place. Forgot to delete the other one.

 

If you like, I can call over to your servicing dealership for you to see what their diagnostic fee is. Send me a pm with the last 8 of your VIN, name, and the name of your servicing dealership.

Regards,
Sarah
GM Customer Service

 

The nearest dealer to me charges $125 diagnostic fee for any car that comes in not under warranty (scan for codes and trouble shoot the problem for an hour before they start working on the car). They tell you what they found wrong, if anything. It sucks that the problem is intermittent though, if you take it to them and they don't find a problem that $125 down the drain.... electrical problems suck...

 

ya I know what you mean, Thats the major reason why Ive been putting up with the intermitant malfuction and putting off getting it fixed. Hopefully itll go hard fault and then we got something to work with. However its possible the BCM stored a fault code that im not seeing with my scanner that only reads PCM faults. I work on aircraft electronics for a living. Avionics are a little more informative about their malfunctions though, even intermitant ones that set a code, the codes are more easily checked and diagnosed and schematics are more user friendly

Ive got a dual interceptor setup, so loosing my instrument display is no biggie since I can still get my RPM/MPH/ and Fuel level on the interceptors. I figure it might be worth to see the codes though.... But for that price im wondering if I can buy a scanner that can read BCM codes as well as PCM codes. Then I only have to pay it once instead of possibly multiple times.

 

I'm not a 100% positive if scanners read bcm codes. I would assume they would read any code that a car is throwing though, whether it be bcm or pcm. I recently got a code for the Transmission control module (TCM) and my code reader read the code U0101, but that was just a failure to communicate with the TCM code. maybe someone with a little more knowledge in this area can chime in?

 

I called up the dealership here, and they want $40 to run a code scan on it. So I made an appt for tuesday, Well see if the BCM threw a code or not.

 

Good to hear, that not too bad, a lot cheaper than the closest dealer to me.. hope its all solved!

 

Okay,
So I went to the Dealership this morning.
They pulled communication codes from my BCM.
U2100, U2105, U2107 and something about power steering and security communication loss.

U2100 = Controller Area Network (CAN) Bus Communication
Can be set by
BCM
EBCM
ECM
IPC
PCM
PSCM
Radio
SDM
TCM
VCIM

U2105 = Lost Communications with Engine Control System
Can be set by
BCM
EBCM
PSCM
TCM

U2107= Lost Communications with Body Control System
Can be set by
EBCM
ECM
IPC
PCM

I'm not sure what all those acronyms are but it seems like they would be set by the PCM, BCM, Power Steering Control Module, and the guy said somethign about security, Anti-Theft.

He also showed me how my key pulls out slightly while in the ignition turned on. He said its not suposed to wiggle that much. On the way home I wiggled it many times in an attempt to induce a fault without success.

The guy cleared all the codes for me. They also found P0171 System Too Lean but thats because of my canned tune so I told them to ignore that one.

Well reading the fault procedures for P2100 it says to check for shorting in the bus so when I get a chance, that's what I'll do next. It also talks about it being itermitant wich is the way my malfunction likes to operate. If its soem damaged wireing, hopefully I should be able to repair it no problem Now that I've kind of narrowed down where to look, I think.

 

M 2007 LS is having this same problem. Did you figure it out? Really need to fix it asap. Thanks for anyones help.

 

My car hasnt messed up in a while since I Posted this. Havnt had time to ohm things out yet, Maybe ill do it this weekend since its a 3 day weekend I'll post results to let you guys know. Did you get your codes checked? The AutZone code reader isnt enough you have to get them checked with a Tech II to see the non pcm codes. Were they the same as mine?

 

Hi! Watch this High speed CAN bus diagnostic resistance check - YouTube

 

I would love to know what the REAL issue is here. Clearly there is some severe electrical fault in these cars. Whether it be a loose ground or short. My automatic 07 Cobalt LS has a similar issue except the AC stops working and the transmission shifts harsh and early. Power steering also goes away.

Like you, not worth paying a diag fee when I know they won't find it. Doubtful a scan tool would even find it. Just lead you down 20 potential paths. Without going over every single ground and wire in the car it may be a worthless chase.

Some have replaced TCM's and had success, others have only had it for a short time before the problem returned.

I had it happen twice but it hasn't happened again in 3 weeks now.

 

I havnt had a problem in quite some time. Stil havnt gotten arround to checking the wireing/databus.

 

2005 Cobalt SS gauges going crazy. - YouTube

 

Ok I just got back from outside messing with my car and looking through the service manual schemaitcs. I ohmed out from the dataplug port like that video showes and wiggled the wires to the Power Steering Controler. I got the 61 Ohms that it shows in the video, no fluxcuation. I Poped off the panel on the passanger side and looked at the connections to the PCM. They were all good. Looked almost new. Poped off plug 2 and made sure nothing looked suspicious on the connections. Nope all is okay there. A few things though

When the malfunction occured, my dual interceptors continued to operate normally. I noticed that since they plug into the data port and get power from the PCM that they must be running on the high speed bus.

The Highspeed Databus goes to, in series the following items (Spific to my car, 2006 SS/SC with Dual Interceptors, No Onstar)

• Powertrain Control Module (PCM)
• Electronic Brake Control Module (EBCM)
• Body Control Module (BCM)
• Electronic Power Steering Control Module (EPS)
• DataLink Connector (DLC)
• Dual Interceptors

The GMLAN or Lowspeed Databus is as follows

• Body Control Module (BCM)
• Radio
• Instrument Panel Cluster (IPM)
• Inflatable Restraint Sensing and Diagnostic Module (SDM)

All of the GMLAN Lowspeed databus items connect together at "Splice Pack SP200"
Does anyone know where Splice Pack SP200 is? I'd really like to have a look at it.

Important note: When the malfunction occuers on my car, my interceptors contune to operate normally. This tells me that the Highspeed databus is operating. If the Power Steering Module or wireing there were to interupt the data, then the Interceptors would be dead. At one point I tried to put the Interceptors at Fastest datarate, but it never caused the fault. I supose it's possible that the interceptors may cause the fault and still read, if they hog the entire databus bandwidth or something.

Does anyone who has had this malfunction NOT have interceptors? Or any other device on the DLC?

A while ago I had my car scanned for non PCM codes Found

• U2100 Controller Area Network (CAN) Bus Communication
• U2105 Lost Communications With Engine Control System
• U2107 Lost Communications With Body Control System

Also the Power Steering Module stored U2100. As we know the Power Steering Module is on the High Speed Bus and feeds the Interceptors.

The DTC U2105 - U 2199 paragraph reads
Modules connected to the GMLAN serial data circuits monitor for serial data communications, during normal vehicle operation. Operating information and commands are exchanged among the modules. The modules have programmed information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are also supervised and some periodic messages are used b y the receiver modules as an availability indication of the transmitter module. The supervision time-out period is 250 ms. Each message contains the identification number of the transmitter module. When a message that indicates the availability of the transmitter module is notreceived, the receiver module sets a DTC 21xx where xx is equal to the 2-digit identification number of the transmitter module. The DTC descriptors listed below provide a method for determining wich module is not communicating. A module with a GMLAN serial data circuit malfunction or which loses power during the current ignition cycle will have a Loss of Communication DTC set by other modules that depend on information from that failed module. The modules that can communicate will set a DTC indicating the module that cannot communicate."

Everything here reads like the malfunction is somewhere on the Low Speed GMLAN. Confusing part is how the Power Steering Module knew about the comm failure, since it doesnt talk on the Low Speed GMLAN but only on the High Speed bus, while during the failure continued to feed data to the Interceptors. If the Interceptors were bogging down the High Speed Bus, the Low Speed bus would still be working fine and not set a code for it. Or maybe I'm missing something. If anyone has any input it would be appricated.

 

check the BCM screws are tight and all the bcm fuses and connectors are properly plugged in. my suggestion

 

Sounds like some one had this issue back in 2008
https://www.cobaltss.net/forums/prob...g-dead-105532/

I Checked thats all good.....

 

Any updates?

 

I check my connections and what not, Everything is fine, nothing was loose. I havn't had it "fail" on me in several months. It last failed around the time I made this thread. I even drove it AutoX and Up to Michigan, ZZP, Wisconsin and back here to Alabama, then to Orlando and back. No problems. Maybe it'll happen tomarrow, maybe it'll never happen again.

I HATE intermitant problems, because of their nature they are very difficult to track down.

If It fails and STAYS failed, I'll have something I can work with.

But its been fine, havnt even thought about it in a while. Interceptors seem to stay working so if it fails again I can get my MPH off of that.

 

Well this just happened to me twice now. Once about a month ago on a very cold night after I just started the car and now today on my way somewhere while I was coming to a stop light. Car kept running, no issues at all, no sputter, no nothing. I really don't want something serious to happen though.

 

I think it's some sort of databus error. It seems to be on the Low Speed side. Interceptors continue to work and I think they are on the High Speed bus. Seems to screw with the security system too. That means worse case you'd have to pushstart your car. Every time Ive come to a stop though while the malfunction was occuring it would go away. I'll have to wait till it breaks hard before I can really troubleshoot it. I hate intermitant, but consistant I can work with.

 

I was having the same problem. Now my car won't even start. Haven't started it since new years eve. I think the bcm is shot I have no idea

 

I really don't want to have to push start my car at all. Insylem, of all the times it happened to you, did your car turn off ever while it was running?

dontcryemokid, that's a problem. Do you know if this is an expensive repair? I don't want to wait until these things happen to get it cleared.


Also all jokes aside, totally serious, how does one actually push start a car? I've never seen it done except in movies and c'mon those are a terrible source and yes I have a manual.