Cranking/Starting Voltage question

[MattW]

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.

[pops98]

I am no expert, but my starting sequence is very close to what you describe. I never paid much attention to it, but just checked.
As far as the voltage while running, I think your system is probably fine. I did not realize normal battery voltage is 12.5-12.7. That is what your gauge is showing at idle and when you accelerate the output from the alternator should rise slightly.
Again I am no expert in electronics, but I think you should be fine.

[Y2Kvert4me]

Originally Posted by Wadoka

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.

This sounds fairly normal, the only part that doesn't, is the 6-10 second delay before seeing the voltage go up after starting.

Mine (2001) bounces up to 14v almost immediately after starting, but if I recall, you have an older C5, and according to what I've read, the 97-99 cars were unique, and changes/improvements were made to the alternator and charging control since those years, so this might be fully normal for your car. If you are not seeing "charge system fault" messages after startup, things are probably fine.


Though I've had plenty of disagreements with him over the years, and don't always take his word as gospel, read the posts by Evil-Twin in this thread, (especially post 16) and/or search for more alternator post by him. In this specific area, he DOES know what he's talking about, especially for the earlier year C5s.

[simpleman68]

I would check over the body grounds. I had this same problem; nearly to the "T" and after cleaning the body grounds all was good again.
Bill Curlee had this in C5 Tech on the other forum.

My ground problem was the two in the engine bay behind the head light on the frame rail. Ridiculously small screw that was completely unprotected from the elements.

Let me know if you need a link to pics of the ground points, or you can't find Bill's sticky.
Scott