I went out to the local Red Cross to give them a pint of O+ goodness yesterday. This weekend always seems like a great time to give, every year.

No good deed, etc. Came back out to the car 35 minutes after parking, and I had a totally dead system - no SECURITY light, no IP test, no switch or starter click - and an odd buzzing noise from one of the relays in the footwell fusebox when I opened the right door. But the column lock solenoid could still be heard to cycle, the mirror reading lights still worked.

I got a jumpstart, and drove out to an Autozone. The whole time, my Voltmeter was fluctuating a lot. Could hear the occasional buzz/sizzle from the footwell fusebox and the voltmeter needle would dip every time a buzz was heard.

Volts would go from 12.5 down to as low as 7.9, especially idling at traffic lights. It would drop so low the airbag dash light would blink, and I set several BCM, LDCM and RDCM codes.

Got to Autozone, got diagnosed with a bad battery (of course).

Replaced battery with a "better" battery than had been in the car.

Now, I'm paying a lot of attention to the Voltmeter. When I'm running the car, the volts are staying at a solid 13.2. Idling at traffic lights, the voltage falls slowly... 13.0.... 12.7... 12.5... haven't seen it fall below 12.5.

Don't hear any more buzz/sizzle from the footwell fuse/relay box at all.

...when I crank the car, the car starts up quickly, no hesitation. Started it four times today.

But... the voltmeter needle, on cranking, swings all the way over into the 8-9 volt range. As the car idles, it slowly comes back up to 12+ volts, perhaps over the course of 6-10 seconds.

Is this "normal" behavior for a start event? I never paid attention before, and now I'm paranoid.

 

That voltage cranking is fine as the DIC voltmeter is not that acurate or responsive. Use a DMM if you are worried (preferably an analog as the digital are slow to respond.
Clear all your codes and drive it awhile. Recheck codes and see if anything is reporting.

 

My apologies, when I responded earlier I misread your question. The voltage gauge on the dash responds slowly due to the dampening of the needle. If you start the car the voltage will drop and then gradually rise over a few seconds. That is normal. I pictured a DVM needle on the battery itself when I told you I wasn't seeing that. When I start my car, the dash gauge needle drops below 10 and then it takes about 4 or 5 seconds to slowly move back to 13-14 volts. If it wasn't dampened, vibrations and turns would make it bounce around. I thnk what you are seeing is perfectly normal.

 

The very first thing that you need to go is monitor the actual battery voltage at the battery terminals and compare it to the reading on your volt meter. You can read actual battery voltage in the terminals of the cigar lighter terminals as it is connected to the hot at all times buss.

If you have wild voltage readings and faulty charging symptoms, the first thing that I would check is the main battery terminal on the starter solenoid. The battery charges and powers thru that terminal. Its a common problem and if its loose/dirty/corroded, it will caue issues:



CHARGING Schematic:



Make sure that the Battery terminal on the back of the alternator under the rubber boot is clean and tight also.



Follow this out and see if it solves the problems

 

Also, do not forget that the terminals at the solenoid are electrically hot unless you disconnect the battery first.

 

All I'd add is relax

You had the classic symptoms of a bad battery but with the new one fitted, you can look forward to happy motoring. Don't forget but what you see on the DIC is the alternator output not the battery voltage so it will vary.

Just make sure if your C5 is a weekend driver, either get a battery tender or top off the battery with an overnight charge every now and then.

 

Thanks everyone.

DeeGee, I have never before had a battery simply die on me like this one. Every other dead battery situation I've experienced, the battery has always given me several days' warning - slower and slower cranking, before final kaputski. Those were not C5 cars, though...

Thanks again Bill.

 

I had to replace the battery in my C5 three times in 5 years. All 3 died suddenly. Shut car off and went to start a couple hours later or at the most, the next day. Never had a problem with charging system before or after battery change. The batteries were all proper replacement AC Delco units. As always, heat is probably the biggest factor in Battery failure and with the battery location in the C5 at the back of the motor above the exhaust you can't get much hotter.

Just my 2 cents.

Phil