Hi, I've got a pretty odd problem with my '99 Corvette electrical system. One day I went to start the car, and a ton of warning messages scrolled across the screen, like reduced engine power, shocks inoperable, check this and that and ect, and it would not start. The first thing I checked was the VATS system, which seems to have been bypassed already. So, second, I checked the steering column lock, which had also been bypassed. I charged the battery, and the car started... 15 minutes later (car turned off, just sitting there), the warning messages were scrolling across again. I put the charger back on, and it read 100% charged. So, I had the battery load tested at O'Reilly's and it was fine. When I got back from O'Reilly's and put the battery back in, no warning messages... everything worked fine... until about 15 minutes later. Same thing. So, I figured it was a grounding problem and started pulling ground connections and cleaning them thoroughly (though there was virtually no corrosion). What I'm finding is that when the battery is disconnected, and reconnected, I can start and drive the car with no problems, for as long as I want. When I turn the car off and it sits for 15 minutes to half an hour is when the warning messages reappear. So, I pulled the codes from the DIC when the car was acting normal (within my 15 minute time frame) and after the warning messages began to scroll across. The car throws no current (C) codes within the 15 minutes, but after that, it has no communication with the BCM or HVAC modules, throws current codes U1000, U1064, U1160, U1176 from the 58-SDM module and a few other historic codes, but I assume those are not relevant to this problem. It seems that all of those codes are communications error codes. At this point, it looked like there was definitely a problem with the BCM connections somewhere. I found a forum that listed the relevant fuses for the BCM, so i checked them and they were all fine. However, minifuse #25 did the same thing as disconnecting the battery. The cab lights came on, hood light came on, and the car acted totally normal... for ~15 minutes anyway. I hunted down the ground connector for the BCM, which was located near the battery terminal, and cleaned the connections. I saw on a Corvette forum post by Bill Curlee a problem with corrosion on splice pack 208 (SP-208). Mine was actually located in the cabin, and was very clean. As far as I understand, there is one more grounding location in the cabin that is relevant to the BCM, but I'm not sure where it's at. However, considering that there was no corrosion on any of the engine compartment grounding locations, I have my doubts that a cabin mounted grounding point would be corroded. If anybody has any idea what's going on here, I'd really appreciate some insight. I may be at the point where I just need to have it scanned by a Tech-II or something. Thanks!

 

As these cars get older it gets harder but these are the classic symptoms of a bad battery

Charge it overnight and check the voltage across the terminals (12.6V fully charged)

If it holds the charge - great. If not, it's a new battery. If that fails (and I'd bet money it'll be fine) then post up again.

You still need to run a drain check. I'll pull out an old post that may help.

 

Identifying Battery Problems
The C5 eats batteries unless you take some regular precautions. If your battery continually dies its either the battery which is on its last legs or something on the car.

You also need to look at how you use the car. Is it a daily driver? If so the battery should be getting a good top up every day so you may have a problem.


Is it a DD but you do short trips? If so you'll be taking a lot out of the battery every time you start. For a short trip, say less than about 20 mins, you won’t top it off properly. Eventually it'll drain.

Is it a weekend car. If so, this takes a lot out of your battery. There’s a 20MA drain even dormant. If you don’t drive the car for a reasonable time every week or so, it'll kill the battery. In this case you really do need a battery tender.

You’ll know when your battery is bad. As it gets low you may get strange electrical indications (random warnings and U fault codes). As it gets lower it may drop the memory settings or defaults such as HUD settings. Eventually you’ll get the dreaded chattering relays in the footwell and eventually the lights on the IPC will disappear.

Most batteries can be recharged quite successfully, although AGMs are harder. Start by checking the charge on the battery. Don’t read the DIC when the car is off. The value you see on the DIC is alternator output when the car is running. It will always measure an inaccurately low voltage on the battery when the ignition is off and figures of 11.0V to 11.9V is normal in this case. With the engine on, the voltmeter should show between 13V and 14.5V. You need to measure voltage across the battery terminals using a digital multi meter if possible. A fully charged battery measures 12.7V and a fully discharged battery measures 11.9V. Partially discharged batteries will give a reading somewhere in between.

If the battery is low give it an overnight charge (or put it on a battery tender until you get a fully charged indication) and retest it. A true test is under load and Autozone will do that test for free.
If you have an AGM battery like the Red Top and it has been deeply discharged it's harder to recover it. This might help:
http://www.youtube.com/watch?v=dIoaL3DWWEg

If you’ve recharged it and it still runs down, then you need to start looking for excessive drains. Bill Curlee posted a good method for checking:

http://forums.corvetteforum.com/1567522286-post590.html

There are some common faults which are well known for causing problems:

First to check is the interior lighting rotary switch on the drivers panel. It’s possible for that to be turned on as there’s a setting (fully clockwise) which bypasses the auto off function. Turn it fully counter clockwise and check after about 30 minutes (preferably in the dark) that the interior lights have gone off.

If it’s not the lights something has failed or is badly installed.

Have you fitted an after-market device which draws current? Typically it’s a cellphone charger, radar warner or a similar device that’s the problem.

If still no joy, you need to start pulling fuses to identify the problem.

The power seat switches on the side of both seats are notoriously unreliable. The switch becomes sticky with use and can stick in the “on” position. You shouldn’t damage the motors as they are thermally protected. The fuse may blow so worth checking (Fuse 36 20A in footwell).

The driver’s lumbar motor can also cause issues so check this too (mini fuse 3 15A in footwell). The seat controls connect under the seat. Pull the connector and if the drain stops that’s your problem.

Less common but not unheard of are failures of the headlight motor control module the alternator and the Bose Amplifier under the dash on the driver’s side.

 

So you think it could still be the battery even though it tested fine at O'Reillys? If so, why would it test well but still be a bad battery? Thanks!

 

I would look for frayed wiring in the rubber accordians between the door and the pillar. Pull the rubber and the harness out and check them. Also, look at the harness going to the seats, especially if you have the easy entry on and the seat moves each time you start and stop the car. The comms bus goes through both of these locations and can get shorted out causing that kind of issue. The 15 minute thing is odd but it's an easy place to start checking.

My next guess would be to unplug all the unneccessary modules (doors and seats to start) in case one of them shorts out the bus. The radio could short the bus too but it's harder to unplug.

 

Not necessary. The easiest way to troubleshoot a class 2 issue, is at the Star connectors.

 

It is the connector you need to check. The wires are usually fine. Search...many posts about this.