View Full Version : BCM wiring

10-04-2006, 04:51 PM
I have had an intermittent issue where my Sky won't start. All the electrical accessories still work, but it won't start. I've had it once shut the engine off while driving on the highway. And most recently it's taken to stalling out at random, after it seems to be confused about what gear to be in (automatic).

The problem started about 1000 miles ago. After the no-start problem happened twice and my retailer wasn't able to diagnose why it happened, I had an aftermarket alarm installed.

Now Saturn won't even diagnose my car unless I remove every inch of aftermarket wiring, even though the problem was reported twice prior to installing the alarm.

From all the troubleshooting steps, the problem seems to center around the BCM wiring. If I take it to a non-GM mechanic shop, they're just going to call Saturn for help because no one knows these cars yet. And GM has an order on my car not to help because of the alarm sytem.

I had the alarm disconnected but not removed, and the problem persists, just as it was there before the alarm was in, but now I have no source for help. I don't want to pay another $600 to have the alarm company take out the alarm I just had put in. And then pay it again after they fix the problem. And even at that, I'm not warrantied anymore (not really a problem) for the BCM. The issue is no one will help, and I don't have the money to take out the alarm system.

I told Saturn it would be cheaper for my car to get stolen with no alarm in it (financed by GMAC, thank you) since the factory alarm doesn't protect the car from anything other than the driver's door and ignition key, than to go through all this install-deinstall stuff when there's probably just one wire shorting out that goes to the BCM.

Can anyone recommend a way to get more help? The technical services issue and the customer assistance issue are frozen right now because the last decision by Saturn was not to help unless I strip out the very expensive alarm that keeps my car protected.

It's plenty protected right now, even with the alarm disconnected, because it won't drive more than a few blocks without stalling out.

Before technician was told he couldn't work on the car, he found the following codes, meaning there was a problem, but it's not current anymore.

U2107 (pass), U2106 (pass), U2100 (pass), U2105 (pass), B3055 (pass), C0561 (pass)

I'm sad I can't drive my car, and livid that the dealer is being prohibited from even diagnosing the problem even if I paid them.

Thanks in advance!

10-05-2006, 12:47 AM
After reading about your interesting dilemma I went searching for specifics and wound up on the Saturn chat site. I was told that you (Sky owner) have the factory Passkey III+ anti-theft system. If I'm not mistaken yours is the newest in anti-theft that has an encoded (embedded rfid device) micro chip in your key. I would like to have what your car came with as the key is crucial to allowing the car to start and run. The physical part of the key is not important as is the micro chip embedded in the plastic portion of your key, the piece that you grasp between your thumb and index finger. This is the radio frequency identification device that is commonly known as a transponder. If you have EZ-Pass or a Mobil SpeedPass key you know what I'm describing. These devices require a specific frequency transmitted to the transponder, your key, Mobil SpeedPass, or EZ-Pass, in the vicinity. These devices are immediately activated and respond with their security code. The transmitter, your ignition security equipment, initiates a receiver to receive the code from your key and if the BCM recognizes this code your ignition system is enabled along with the fuel pump. A lack of recognizing this security code from, say a bogus key copy, will just turn on the security light in your instrument panel and disables the ignition and fuel pump. You can turn the engine over all day or until the battery dies but the car won't start/run. In essence, a brilliant security system. Perhaps you aren't fully aware of this feature as your owner's manual probably describes it in better detail. By adding an aftermarket alarm system, and depending on the compatibility of it to your very good anti-theft system, the aftermarket one will have to work in parallel to secure your car from theft.

It is this dilemma that Saturn probably acknowledges as interfering with the factory anti-theft system and brought you to this end. By insisting that the aftermarket alarm be disassembled they can proceed to cta (cover their *****) during the remainder of your warranty (if it is still valid). It is your choice at this point but if I did this and find that I have this Passkey III+ system I would bite the bullet and have the aftermarket system removed to at least have the factory warranty retained. After all, if your suspicions are correct about the BCM preventing start and run then the warranty should cover the expen$ive replacement. If you are wrong the removal of the aftermarket alarm should allow a return to normal start and run conditions. The Saturn warranty, service, and customer relations are restored and you have your new car back on the road, albeit w/o the aftermarket alarm.

BTW, since having a remote start installed in my L300 I've encountered several occasions when my car couldn't start remotely and when I entered my car to manually start, my engine would turn but not run. After the mandatory factory security wait time I was able to start and go. I found that if the remote failed to start I could press the brake pedal to disable the aftermarket remote start circuit and then was able to start my car. It took several attempts, each occurring at separate times when this would happen before I tried this technique. This isn't covered in the remote start manual and the feature of my remote start is probably the same as other remote start products, that they retain the factory anti-theft system. I first began to blame the remote start for enabling the anti-theft system preventing me from going about my business. I gave this some thought that the remote start circuit (upon failure to start/run) falls back to the factory anti-theft system. It make sense that I attempted to restart the car after a failed remote start and the circuitry times out to engage the factory anti-theft. Its a long story but I felt it may help you to see things from another point of view. I still use my remote start and have familiarity with one feature to allow a longer time to engage the starter. Useful in cold weather as any car may require a little longer time for the starter before ignition occurs.

10-05-2006, 07:43 AM
Thanks. We originally investigated the chance that the car was not recognizing my key. I have several. The same no-start occurred with all the keys, even before the aftermarket alarm was installed. I do not have remote start for two reasons, one it is illegal here to let your car run when you aren't in it, and two, precisely because remote start is even more invasive as far as affecting the factory security process. The dealer said that there were no codes indicating a passkey III failure and that this was not the original problem. I wish it were that easy.

Removing the aftermarket alarm unfortunately will not restore my warranty of this area of the car though. I seriously pissed off some Sky engineer when they found out the alarm tapped two BCM wires, and I think his apparent rage has inspired the "no-help" policy.

I'm still looking. I think it's just a bad wire, but not sure how to identify which one. One of the reasons that it is most likely wiring, not a security conflict is that jiggling the bundle of wires connected to the BCM has twice allowed the car to start when it wouldn't. The car shut down when there was a passenger whose feet rested on the carpet covering these wires. And kicking this same floor panel that covers the wires was all it took to start the car when it shut off and wouldn't start. If it were a Passkey feature, this wouldn't have changed anything about the starting.

10-05-2006, 07:45 AM
That reminds me, any idea where I can get a wiring diagram for the BCM? It might help me make a better first selection if I'm going to look for a faulty wire connected to it. Saturn would normally replace each wire for $55 each, but not for me right now.

10-05-2006, 08:48 AM
I'm sorry for your unfortunate situation; I bought the factory service manual to stay on top of my maintenance. My remote start is no more invasive than your aftermarket alarm as it required a bypass module to 'fool' the anti-theft system while allowing the car to run for a set time period. After this time period (preset for 5, 10, 20, 30 minutes, etc.) elapses and the ignition key isn't inserted to the run position the remote start circuitry disables engine running. It then allows the factory anti-theft system to protect the vehicle. While the key is left out and the remote is bypassing the anti-theft any brake pedal application (required in my car to shift the xmission) or opening the engine hood automatically signals the remote start circuit to disable the engine, a safety feature since the steering column lock won't allow turning. Its a decent setup and works very well, I just had to learn the intricate idiosyncrasies of this sequence. Looking at this from another point of view, the remote start will stop engine running if one wanted to pre-warm or pre-cool the car interior w/o you being around. Of course the car shouldn't be run in an enclosed garage but the time-out feature can be used to advantage while having the anti-theft system left intact.

By your description you may be able to isolate the wiring if you carefully go about it with any and all the info necessary to help you. Having the schematic diagram will certainly help. Have you tried Alldata? I think there's a small fee for online data, if not perhaps someone else can make a suggestion as to where you may have access to wiring diagrams. If you are adept with a multimeter you'll certainly be able to find the possible break in wiring. Just be sure to know when to disable power or to have it when probing around the BCM harnesses. You don't want to add anymore problems if you inadvertently short-circuit anything in the BCM harness. And if you are still sure of a break in wiring it may not be obvious if wiring insulation isn't cut or chafed but separated internally. Reading your last post is like throwing down the gauntlet and challenges me to have a desire to help you. It appears that your harness may be incorrectly routed to allow this situation to occur. Anyway, good luck with finding the info and please keep us in the loop as to what transpires. If I can be of anymore assistance I'm just a few keystrokes away. Time for my :sleep:

10-05-2006, 09:06 AM
Thanks, any help is much appreciated. I went to Alldata.com but they don't show any listings for 2007 cars, only up to 2005, so I wrote them a note. I'm pretty good with a multimeter. I will talk to the service associate who I get along with pretty well and see if she can point me to another source where I might get wiring diagrams. Either that, or I'll get out some very tiny dousing rods and start passing them over each wire, heheh.

Meanwhile the car is undrivable. *sigh* Mostly it is just embarrassing because I have been a Saturn zealot for about 12 years and I waited for this car since I first heard about it almost 4 years ago.

Of course, I could just tell folks I have the only Sky with a kick-starter!

10-06-2006, 02:45 PM
Well the folks at Alldata said they haven't even gotten to posting 2006 diagrams so 2007 diagrams won't be available for a year. My service advisor said that the GMDealer web site does not have any wiring diagrams for the Sky either. I asked her to inquire regardless because if they ever do work on my car, they'll have to get these wiring diagrams from someone at GM.

It's been raining since yesterday so I've not been out under the dash trying to look myself. I'd be soggy.

I need to pull out my alumni directory and see if I have any GM execs in the book.

10-12-2006, 07:30 PM
hey bro sorry to hear about your experience with you saturn dealership. Anyways i don't understand why you should be scared oF people stealing your car unless you don't have full coverage insurance. Also the on;y way they are able to take your car is if they roll it away...Anyways here are the codes Def.

DTC U2107: Lost Communication With Body Control Module (BCM)
DTC U2106: Lost Communication With Transmission Control Module (TCM)
DTC U2105: Lost Communication With Engine Control Module (ECM)
DTC U2100 Controller Area Network (CAN) Bus Communication
DTC B3055: No Transponder Modulation or No Transponder
DTC C0561: System Disabled Information Stored

Let me know if i can help you anymore.

10-12-2006, 07:43 PM
Thanks for the codes.

Well, I would be without a car if the stole it and would have to wait half a year for the next one to roll off the line with my name on it, but since that's the least likely thing to happen...

It's the fact they can vandalize the car and not set off the alarm with just the factory alarm that bothers me. And also that with the top down, they can reach into the glove box and the console compartment and take my registration, ez-pass, whatever is in there and not set off the factory alarm.

I want it to shriek when someone reaches inside my car, when anyone leans against it and could scratch the paint with the zippers in their cargo pants, when they bump it in the parking lot by carelessly opening their door, etc.

People are mean, and some of them jealous. In my parking garage new cars have had tires slashed, paint dumped on them, antennas ripped off, and all seemingly for lack of any other entertainment for these vandals. I at least want a chance to catch them if the alarm goes off which beeps the remote in my house. I don't even live in a "bad" neighborhood, just near a subway station.

Regardless, I spoke to the regional director for Saturn corporate today and he said I'm the only one he knows of with something wrong with their Sky. He read me a letter from John Bon Jovi about how much he loves his new Sky, and he said the only difference between me and Bon Jovi is that my Sky isn't working, so we need to get my Sky working. I have confidence that the electrical issue will be resolved this week after he makes some other phone calls and my retailer is on-track to help me again. It was suggested that the less than helpful stance was initiated by a contractor that works for Customer Assistance, and that the right thing to do is to fix the car, so that's what I expect to come down the line next.

Thanks for the great feedback. I can't wait to get driving my Sky again!

10-12-2006, 08:21 PM
Hey, just when things start to look bleak a ray of sunshine peaks out from the clouds! Glad to hear that a discussion with the regional rep has turned things around for you. I'll keep my fingers crossed....................................after all, we mustn't keep your Sky down!?

10-13-2006, 12:24 PM
Now that is what I'm talking about. I would have to laugh at the local Saturn dealership that brush you off...We had the customer that came to our dealership that towed his VUE in park behind a diesel pusher and blow up the tranny. It was obvious that he cause his own mistake because all the tires had flat spots on it and the vehicle only had 5K on it. Guess what SAturn was aware about the situation but to keep him happy they warrantied a brand tranny authorized by the area rep. See what Saturn Corp would do for their customers.

03-14-2009, 11:08 PM
I have been to the Sky / Solstice assembly plant in Wilmington Delaware a few times (business), other than that, I know very little about the Sky. Cool looking car!

Anyway, the problem looks like your CAN communication are corrupt or shorted.

You might be in luckÖ the CAN bus wires are always a twisted pair. Easy to identify even if you donít know the color code or schematic.

You indicate that kicking the floor panel will sometimes allow the car to start again. Perhaps this is a good place to start looking.

The CAN bus allows communication between various components within the vehicle. If the harness is not damaged then you may have a failing component. For example, the instrument panel is on the CAN bus. It is possible that a failing instrument panel could cause a CAN communication failure. I think the HVAC controller is also connected to CAN. Some of the newer Delphi sound systems are within the CAN network.

I just read on the internet that some aftermarket alarm systems are connected to the CAN bus. I think this is mostly for remote start (you donít have). Anyway, You might want to check just in case.

Best of luck!

03-17-2009, 09:05 AM
First of all, it's mounted in a really bad place. I would disconnect the BCM connector and check all of the terminals for tightness and corrosion. Also, on your U-codes... do you know which module is setting these? that would help send you in a direction. We've had to replace some of these BCMs that just plain had an internal fault. When you reconnect the connector pack it with dielectric grease to keep moisture out. If you need some schematics on the BCM I might be able to help but it may take a minute or so. Sounds like the dealership you took it to didn't know what they were doing or just didn't want to go through the hassle of correctly diagnosing it. They should have at least called TAC (technical assistance center).
Hope this helps.

Gerry Proctor
03-17-2009, 09:46 AM
This post is a couple years old, guys. The original poster's circumstances have no doubt changed over those years and it's not a common problem.