Air bag and SES light on constantly

[billyb22]

My Mother-in-law owns a very nice 1999 Regal LS 3800, 80,000 miles.
She calls me the other day from a parking lot where her car won't start. I go expecting to jump start the car. When I pull the positive cap off the battery, the entire side post/lead insert falls out of the battery with the cable still attached. Battery acid is leaking out of the hole. I removed the junk battery and put in a brand new replacement. Car starts fine, and I follow her home. All exterior lights work including brakes and blinkers. The dash lights, stereo display, and HVAC display, disappear when the headlights come on manually or automatically. I could not get the dome lights to come on at all with the dimmer dial. The SERVICE ENGINE SOON light and the AIRBAG icon are lit continually when the car is running. I can't find a bad fuse and the guys at Autozone claim there is no code other than a loose gas cap code that they say is very typical for this car. Before the battery decided to have a meltdown, the car was fine - no problems. I would appreciate any and all suggestions. Thanks in advance.

[BNaylor]

If that was the original AC Delco battery that is a common problem as far as the positive terminal. If it is the OEM battery I'm surprised it lasted that long.

It sounds like you are missing 12 volts to certain circuits like DRL and IP circuits including possibly body control module (BCM). Although fuses may look good have you checked for 12 volts at the fuse sockets with ignition to on?

Disconnect the battery negative cable overnight and reconnect the next day, then see what it does.

[billyb22]

I too was shocked to see that, in fact, the original battery was still in use.
It was the ol' AC Delco with the foam blanket wrap.
Do you think it might be in the electrical center under the hood, or beside the dash?
It seems like this car has more fuses than the average car. I was hoping for a good place to start - I don't see any fuses labeled dome or courtesy as I would expect.
What will taking the negative battery cable off do? I would think that the positive cable would have more to do with it. I just want to fully understand what I'm doing under there.
Thanks alot for your reply.

[BNaylor]

Thats about right on the AC Delco battery. I replaced the one in my '99 Regal LS (115K miles) back in 2004. Lasted about 4 - 5 years.

The best thing to do is look in the owner's manual Chapter 6. The courtesy lamp fuses should be marked interior lights or inadver power/rap, etc. Probably shared with other components. The component that controls the interior courtesy lamps via RKE or the dimmer knob is the body control module (BCM). So check any fuses marked BCM too. Look in both engine compartment fues box and the one located at the passenger side of the dash.

The purpose of removing the battery negative cable is to force a quasi reset of the PCM module and BCM. It is safer doing negative only.

[billyb22]

Thanks, I'll dig into it and post my findings.

[billyb22]

Since the car is not mine, it is not readily accessable to me. I had my Father-in-law remove the negative battery cable last night at 7pm. I went over this morning at 9:30 and reconnected it. No luck. I guess I need to check each fuse socket next. Isn't it odd how the radio display and hvac display are dark when the car first starts, but when the headlights click off automatically, the displays come back on? I guess there should be two levels of brightness, not off and on.

[BNaylor]

It sounds like the 12 volts to the headlight/dimmer switch is missing. When the headlights are turned on automatically or manually by the pull switch all lamp control to the IP Cluster, HVAC and radio for dimming is via the dimmer control.

Checking voltages sounds like a good idea. You may need a GM wiring diagram of the circuits to help out.

[billyb22]

Thats what I was wondering about. This same circuit could possibly feed the airbag monitor and be causing the SES light to illuminate, right?
Do you have any idea where I can get a diagram for that specific vehicle, the chiltons and Haynes are kind of generic.
Do you think any of this was caused by the positive battery cable coming loose and possibly arcing for a bit before totally becoming disconnected?
Thanks in advance for you response.

[BNaylor]

It sounds like the problems are related to the battery incident but it looks like there is more than one problem now. As far as the SES light staying on maybe there is an odb-ii DTC fault causing it. Did you get it scanned? On the airbag light when you take ignition to run does it flash for a few seconds before staying on?

[billyb22]

My inlaws took it to Autozone the next day after I replaced the battery.
The clerk told them before scanning, that a code would come up about the gas cap? Sure enough - it did. The clerk then scanned again and the code was gone. His suggestion was to buy one of his new gas caps. (they did not)
I drove it around the block this morning after reconnecting the battery cable. I did notice that the airbag light blinked a few times when I first started the car. I was hoping it would stay out, but then remained lit. Thanks

[BNaylor]

For the SES light it looks it may be an actual odb-ii fault setting it off such as the small leak gas cap evaporative emissions code. If the SES light is still staying on then another scan may help to see if the fault is consistent. For small leak the gas cap is the best starting point. The error should clear in a few drive cycles or the DTC may need to be reset with a odb-ii scanner.

The airbag SRS system is detecting a fault with either of the airbags or maybe the battery problem caused a surge affecting this and other components. The device that triggers the air bag light is the SDM module (service and diagnostics module) which the the brain for all airbag monitoring and deployment.

[billyb22]

We could not find anything abnormal. Off to the dealership it goes.
They tell us the BCM is bad and replace it for $425.
OK, the SES and AIRBAG light issue is gone, but they say the headlight switch is also bad, causing the interior lights to be inoperable.
My question: Can I get the AC DELCO part from ROCKAUTO for $55 and replace it myself? The dealership wants over $200 to do it. Is there more to it than just the $55 switch? Thanks

[BNaylor]

If you are sure the headlamp switch is bad I don't see why you can't do the job DIY. Job will be tedious because you will need to remove lower dash covers to get the one piece dash bezel removed. The headlight switch replacement is no problem once dash bezel is removed to gain access.

On the BCM you could get that part yourself and just have the GM dealer do the programming routine. Make sure it matches your year Regal by verifying the GM part numbers. EBay is a good source for BCM modules and Ed Morad who has an EBay store. Good luck.

[billyb22]

The dealership has already replaced the BCM.
We told them "NO" to the switch due to the seemingly high estimate. ($225)
I have ordered the replacement from Rock Auto for $55.
My Mother-in-law is understandably upset at the situation for 2 main reasons:

1) Why did they replace the BCM, when it did not fix the problem?
2) What in the world caused this to happen in the first place?

From what I understand, the BCM was bad, and was only part of the root of the different problems with the car - replace the part that is known to be bad and go from there.

There would have been no problem if the service writer had known about both parts at the time of the first call, instead of saying "this is what needs to be replaced" then calling later to say "we found another bad part"

I still say that when the battery cable had its little meltdown, there was some sort of spike that burned out the BCM - as for the switch, I don't know if it has circuitry that would or could be damaged if a voltage spike occurred.
It has to be a freak coincidence that the 2 parts went bad at exactly the same time - the precise time when the battery problem occurred.

So, the total for the new BCM is $475 - that includes the part, labor to replace the BCM, and the subsequent time afterwards to look into the remaining issue of no panel/dome lights.

She would feel much better if I could tell her that this is not out of line, and that the dealership was most likely honest and followed protocol in trying to determine the extent of needed repairs.

Any other input is appreciated.
Thanks, Bill

[BNaylor]

When it comes to electrical problems it is hard to say whether the cost is out of line. Electrical labor rates are high. Of course, the dealers charge top dollar for parts too. Also, the dealer is your only option because they have the right diagnostics equipment to troubleshoot BCM problems and pull up BCM/Chassis DTCs. I would agree the BCM is susceptible to battery related damage or spikes since it handles anti-theft, remote keyless entry and retained accessory power (RAP) in addition to other functions.

As for the headlamp switch the battery incident may have caused that. The reason why is battery power is on that switch at all times regardless of whether the ignition switch is off.

Good luck and hope it all works out for you.