No electrical power but battery tests OK

[1 BAD 9T9]

I have been cleaning my car (very detailed) for another car show in Michigan. While I do this the doors and trunk are usually open. After several hors there is zero power to open doors, open trunk, turn on park lights etc. I then boosted the battery using cables and everything went back to normal. This first time I pulled the battery and went down to my battery supplier, however he tested the battery and it showed better than new. So I put the battery back in. Next day the same thing happened twice, no power to anything. Boost the battery and it was good. I only charged the battery using the car's alternator for about 5 minutes and the car was just like new - started just fine and everything functioned perfectly even after an overnight in the garage.

Since the battery tested OK I feel the only thing left is the Body Control Module. I guess I will have to look at the codes to see what is going on with the BCM. Has anybody experienced this phenomenon? Any body have different ideas? Thanx!

 

[Murray20c8]

Something alive when the car is off draining the battery other than what's supposed to stay on.
If you have an amp meter that reads up to 10 amps, you could undo the battery cable and see what the draw is. It shouldn't be more than a trickle with he car off.

 

[1 BAD 9T9]

Thanks Murray, but I know what is drawing down battery - it is the door and trunk lights, but the puzzle is why is car thinking battery is bad and then the battery is good after only a boost. First time when I tested what was supposed to be a dead battery it tested 640 cold cranking amps and 12.6 volts = super, better than new. Something in the car is cutting off the power when the voltage drops a little, that is why I thought it was the BCM. Peter

 

[Murray20c8]

Thanks Murray, but I know what is drawing down battery - it is the door and trunk lights, but the puzzle is why is car thinking battery is bad and then the battery is good after only a boost. First time when I tested what was supposed to be a dead battery it tested 640 cold cranking amps and 12.6 volts = super, better than new. Something in the car is cutting off the power when the voltage drops a little, that is why I thought it was the BCM. Peter

I misunderstood. That is weird! Modern tech! Go figure!

 

[cdnrx1]

Hi Peter:

Sorry to hear that you are having electrical issues with your GS. A little more information may help to determine the possible cause of the problem.

1 - Is this the original battery that came with the car? If so, this would be my first choice as to what's causing the problem. The OEM battery, when used under normal conditions and properly maintained, is good for approximately 5 to 7 years of service. Your car appears to fall within that usage period and may have developed an intermittent internal fault(s) that can't be easily detected by basic shop testers.

2 - If it's a replacement battery, when was it installed, is it a conventional sealed lead acid or AGM battery? What make / model is it?

3 - Are you getting any warning info displayed on the DIC? If so, do you have a code reader or can you get your battery supplier to read them for you and provide the results?

If your running the original battery, the first thing I would do is replace it. It's the most likely culprit. If it's a replacement I'd start with a proper load test using a professional battery tester / analyser. I'm not saying that your battery supplier's equipment is not up to par but a correct diagnosis requires the right equipment. You mentioned the the CCA test was done on the battery when it was out of the car and the preferred method would be to run the test with the battery installed in the car using the vehicle's starter. Same for checking alternator output.

As to the BCM being the cause of the problem, it could well be. Leaving the doors and hatch open for an extended period should not cause the problem that you've experience. The BCM should cut the electrical draw after 8 to 10 minutes in order to protect the battery. If that's not happening then the BCM could be the problem or there may be an unrelated parasitic draw taking power directly from the battery.

Let us know the answers to the above questions, maybe we can provide some additional information.

Best regards
Ross

 

[1 BAD 9T9]

Ross, thanks for the advice.

I have a very knowledgeable Corvette advisor who has told me with the car in neutral that the infotainment system will draw the battery down very quickly. When this happens the BCM shuts down the system similar to the shut down if you have extended stationary idling. Because after I boost the car the battery does not even need a charge be operational I know it is not the battery. Plus I had the battery tested and it is better than new. What's left - the BCM which is only doing what it is supposed to do. All is good now so thanks everyone for all of your input. Peter

 

[1 BAD 9T9]

Further information on my electrical problems. Yes it is the BCM and here is why.

When I clean the wheels for a car show I jacked up one side high enough to be able to rotate both front and rear wheels plus put the automatic trans in neutral. I thought this was a brilliant idea however the BCM or computer thought differently. Here is what it saw - car in neutral rear wheel turning, front wheel stationary .....bingo! It thinks "this car is being stolen" and shuts everything down.

I think this is now the end of this story.

 

[sharkface]

almost all problems like this with Corvettes are a bad ground somewhere
Jay Leno's z06 had a bad ground in the drivers door that kept the whole car malfunctioning