Service Vehicle Soon Light


Old 02-02-10, 01:29 PM
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Join Date: Mar 2009
Location: Texas
Posts: 1,051
Service Vehicle Soon Light

The SVS lamp comes on once in a while on my '05 Equinox. On the newer GM products I believe this light is triggered from the Body Control Module which deals with electrical functions verses the Service Engine Soon light which is typically tied to emissions. All the lamps are working on the vehicle. It will come on every few weeks, but will cancel after a restart and stay off for several weeks after that, only to flash on again and repeat the same scenario. Just wondering if anyone has seen this before on recent GM products. BCM codes will not show up with a regular OBD2 scan and I believe require the more expensive GM version. I was wondering if this situation was due to some kind of phantom signal from the BCM. Any thoughts?
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Old 02-02-10, 05:43 PM
Join Date: Oct 2008
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These newer vehicles can have 24 to 80 different computers and 3 different computer local area networks.

For example the driver may press a button to roll down the passenger window. The signal goes to a computer in the driver's door, that sends the signal out over a computer network. Then a computer in the passenger door picks up the signal from the computer network, then activates the passenger window!

Pretty much they are able to replace large wire bundles with all these computers. All they need is power and a computer network connection, then can control everything with that.

Anyway this means computers for everything! (Even an electric seat!)

I've seen some new do-it-yourself scanners on the internet, which in addition to the engine computer can scan the ABS brake computer and maybe the air bag computer. I don't know if any of them will scan the HVAC computer?

Anyway there are a LOT of other computers which they can't scan. And you would need a $3000 Tech II scanner for everything.

Then also GM diagnostic software you get here...

And then a factory service manual set to explain what the code(s) means and troubleshooting instructions (order from dealer or

Probably best to take it to a GM dealer for diagnosis.

Here is a good book on the future of vehicle electronics...
"Automotive Electrics and Automotive Electronics" Bosch...
Bosch Handbook for Automotive Electrics - Automotive Electronics - 5th Edition - Bentley Publishers - Repair Manuals and Automotive Books

More about GMLAN vehicle computer networks...
Why the GMLAN

Controller area network - Wikipedia, the free encyclopedia

TECH II Scanner...
Tech 2
Old 02-02-10, 07:56 PM
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Join Date: Mar 2009
Location: Texas
Posts: 1,051
Great information Bill190. I knew that some electric commands were passed through a BCM, but had no idea to the extent that this technology is now used for everything including HVAC and transmission controls. This technology is clearly pushing diagnostics back to the dealer, or to skilled and well trained techs. I did notice a hard downshift this last time when the SVS light came on during my first stop after starting the vehicle and driving a block, but figured that the fluid perhaps was just cold, though the outside temperature was not that cold around 38 deg. Normally the shifts are consistently smooth with the Aisin transmission. I know it is maintenance time to change the transmission fluid, and clean the filter for one thing, and it appears that even this information can be detected and shown as a fault according to what I read in one of the links. I will get the vehicle into a dealer for a scan at least to make sure I know what is going on, and to confirm whether there is anything further I can do, or whether I need the help of a tech with this. My transmission is pretty much a sealed system also, with not even an obvious filler tube or dip stick. As older vehicles continue to disappear so too will alot more of the DIY work that we talk about on this forum. Most of the posts around fault codes in this forum are for older vehicles, and involve basic emission sensor type failures. Makes me a little sad thinking about what will be left for a DIYer to tackle in the next 10 years. It seems that it won't be much.
Old 02-02-10, 10:20 PM
Join Date: Oct 2008
Posts: 1,312
No there will still be plenty of DIY stuff to do. You just need the factory manual set and a multimeter and can do quite a bit.

I don't know about the code reading part though. The future seems to be heading toward a PC connected to the internet and this plugged into the vehicle.

I would expect to see code readers available which will do more and more. Or perhaps software for a PC and a cable to connect to your vehicle. This is available now for older vehicles. Like here...
ALDL OBD1 OBD cable OBDI OBD2 engine codes
Old 02-02-10, 10:37 PM
Join Date: Oct 2008
Posts: 1,312
Here is a peek into the future...

General Motors MDI...
(Scroll down to read more past product info)
General Motors MDI (Multiple Diagnostic Interface)wireless
Old 02-03-10, 10:29 AM
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Join Date: Mar 2009
Location: Texas
Posts: 1,051
I still miss gapping points, leaning for best idle, and chalking the TDC pulley mark to set the timing. Had a short stroke 283 once that would fire up to rumble with a 1/4 second hit on the starter after doing things the old school way. Didn't need to buy many major parts either, just alot of different repair or rebuild kits full of bits and pieces. That was DIY at it's best. Someday people will talk about today's cars the same way. I probably won't be one of them though. PLug and play for me just isn't the same.
Old 02-03-10, 10:47 AM
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Its entirely possible that we may live to see the day where engines and transmissions are not repaired at all..but just unplugged and replaced. There is already similar talk of that with some electric(?) or fuel cell (?) vehicles. You don't refuel/charge pull into a bay and an automated system swaps the module in a few minutes.

Look at how long it takes to change engines in a modern jet fighter (or is that fighter or helicopter...seems like its just a couple of hours or less? Thats for two very advanced and complicated machines.

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