Mysterious starting problem

[Eric540i]

After not having been used for 2 or 3 days after a long freeway trip I tried to start my car. The engine cranked over - and appeared to fleetingly start (a fraction of a second) - but nothing more. The warning message TRANS PROGRAM also appeared.

Checking fuses and just making a superficial inspection of the engine bay, nothing appeared untoward, so I tried again, and again, until the battery failed.

A few minutes later I jumpered another’s battery and after 4 or 5 seconds cranking the engine started normally and the TRANS PROGRAM message disappeared. Since then I’ve had no problems starting and the car’s run fine but, not knowing the problem, I don’t feel at ease and I’m wary that it might happen again.

Does anyone have any ideas what caused my starting problem?

I’d normally suspect an ignition or fuel fault, but I can’t fathom the TRANS PROGRAM warning.

[BillionPa]

trans program is caused by the voltage being too low. either your battery is on its way out, or the alternator is.

or... you may have a current drain somewhere that lowered the batt voltage during its 3 day slumber.

[tim]

When's the last time you looked at the water levels in your battery? I second the low voltage opinion.

[Eric540i]

My battery's only 6 months old and most of the driving I do consists of long distance stuff rather than draining short trips. I admit I haven't yet checked its water levels though.
What puzzles me is that the starter motor engaged with the same 'verve' as usual, whereas if the battery was at fault I would have expected some sluggishness.

[tim]

The starter motor doesn't care what the voltage is. When you turn it over you are probably dropping the voltage of the battery below 11v. When you pull 100+ amps out of a nominal 12v battery when its actual voltage is 10.8 volts or less, you permanently reduce its capacity to recharge. Worse if the water is low.

Since yours is pretty new, and the alternator seems to work, another possibility is that you have a bad cell within the battery. Lead acid batteries are really 6 cells with 2.1 nominal voltage each, connected in series. Sometimes, if discharged too low, a cell can reverse, or lose it's ability to recharge as sulphate cakes up on the lead electrode. Sometimes you can get a bad one regardless of age or abuse.

You can use a multimeter to check this to be sure, before you go out and buy a new battery. If you have to buy a new one, I recommend Autozone's -the 58-D if memory serves- do a search to make sure.

P.S. You can use the multimeter at the positive terminal on your valve cover (the one with the cover on it, and just put the black on the block or over at the ground terminal next to the strut tower. It doesn't really matter where you take the voltage.

-tim

[Thayne]

Might want to check your alternator.

[Eric540i]

I checked my battery's water levels and effectively they were lower than they should be.
I'll replenish the cells with some distilled water tomorrow.
Many thanks for the advice.
I've always had no-maintenance batteries and thus never had to check water levels. I found the following useful page for anyone who's as ignorant as I was:

http://www.justbajan.com/cars/maintain/052501-01/care.htm

Another question: while accessing the battery under the rear seat I noticed a pressure switch which appears to close when the seat is in place. Does anyone know what this is for?

[BillionPa]

security system.