OT: Automobile electrical systems

[saab2000]

This place has always had a wealth of knowledge on all subjects bicycle.

Now I'm calling on the collective automotive knowledge.

I own a 1998 GMC Yukon. It's a full-size sport utility vehicle and is fundamentally in good shape. No rust. 120,000 miles.

Here's the problem. I'll preface it with some background that I believe to be unrelated.

Last year about this time the vehicle was found with a dead battery. Got it jumped. Drove it around to charge the battery. Didn't work. Got a new battery. Then I noticed the alternator/charge gauge was erratic. Had a new alternator installed. Works like a charm for the next 12 months.

Then about 2 weeks ago my brother (with whom I share the vehicle when I'm not around, which can be weeks at a time) found a dead battery again. Had it jumped. Drove it around for an hour to charge the battery. The charge gauge is right where it should be, indicating a good alternator.

The next day the truck fired up immediately. Then he let it sit for about 10 days. Fired it up. No problem. The next day it wouldn't start. Nothing.

There are no lights being left on and nothing to drain the battery. I'm quite certain there is a short in the system in the ignition and it somehow wasn't shut off completely. There must be something draining the battery.

Has anyone had experience with this sort of thing? I believe it to be a short but I'm no expert. I don't believe it to be a bad battery, though it could be. I'm open to a new battery but I'd like to figure out if there's a short killing the battery before I get a new one.

I'm going to bring it in tomorrow to a mechanic I trust but I'd like to go armed with some knowledge first. I'll share everything I know about this case with him.

Just trying to educate myself. I know there are some automotive tinkerers here and someone might have some hints.

[alancw3]

possibly corrosion on the battery terminals. also loose battery terminals that retard the charging of the battery. sitting for 10 days. i have a car that sits for long periods w/o running and then sometimes runs for a brief period. the battery does discharge. i finally bought a deltran "battery tender junior" at walmart for $35 which i plug in and keep the battery fully charged for the weeks i don't drive the car. car batteries need to be kept charged. boats use a "deep cycle" battery that is designed to go long periods w/o charging. if it were me i would try a battery tender before going to mechanic. just saying!

[pbarry]

Do you have a ohm meter? See if the battery is really dead. Power may not be getting to the starter. The battery wouldn't lose charge completely overnight without a drain on it. Your mechanic will start by testing the battery, then test the alternator output, and go from there. The fact that it's been holding a charge points to bad wiring.

With the age of the Yukon, it might have a loose connection, worn wires, or corrosion somewhere. Check the leads from the battery to starter relay, lead to starter, and especially, the ground wire for corrosion and kinks that may indicate a broken wire. Check the mounting tab on the ground wire where it meets the frame. Sandpaper, a wire brush and dielectric grease may solve it.

Look over the fuse boxes. There should be one under the dash, and another in the engine compartment. Look for corrosion on connectors, loose wires, and evidence of water entering. A leaky windshield can drip onto the harness and fuse box under the dash on some vehicles.

[biker72]

My first Toyota battery lasted almost 8 years. The second lasted 8 months.

You could have another bad battery.

Try the trickle charger method posted by alancw3 first and check for battery cable/terminal problems.
Is there any warranty left on your battery...?

[saab2000]

I agree about the slow discharge except that it would sit for weeks and start with no issue and then overnight lose the charge completely.

I'm trying to get a neighbor to jump it in a few minutes.

Hopefully I can get a good charge.

I don't really need two vehicles and as soon as some moving is done this vehicle goes, or at least goes off my name and insurance and maintenance dime. My brother wants it next.

It was my father's and he gave it to me before he went to that big GMC truck garage in the sky. It's a bit of a family heirloom and nobody says they want a truck this useful but they're always glad someone in the family has one.

It seems you never have more friends than when you have a very capable truck.

[pbarry]

Jumping it and relying on the alternator to recharge it won't help ulitimately if you've got wiring issues. Can you borrow a charger? Or, take the battery to an auto parts store. They can test it and charge it for you, usually free.

[dogdriver]

Most likely corroded battery terminals, especially if it works like a charm one day and is dead the next day. Either clean or replace.

Possible bad ground, check connection on both ends of negative battery terminal cable.

Beyond these two, you go down the rabbit hole of aging auto electrical issues. Good luck! I'd suggest either a visit to a decent mechanic or post the question on Cartalk.com-- lots of auto-geeks (this meant as a compliment) who will share their knowledge... kind of like a car version of here...

[saab2000]

Thanks all!

[rePhil]

Could be the diodes in the alternator.

[dustyrider]

I once chased an electrical problem from battery(iffy reading), to alternator(funky amperage jump), to starter(wouldn't crank), to spark plug wires(desperate). After a weekend of chasing grounds under the dash, I hooked the meter up to the battery cables and sure enough...the main ground was in and out. Must have been a $20 fix that I spent a few hundred on! Sometimes I tend to over-think things.:rolleyes:

[rwsaunders]

Most likely corroded battery terminals, especially if it works like a charm one day and is dead the next day. Either clean or replace.

Possible bad ground, check connection on both ends of negative battery terminal cable.

Beyond these two, you go down the rabbit hole of aging auto electrical issues. Good luck! I'd suggest either a visit to a decent mechanic or post the question on Cartalk.com-- lots of auto-geeks (this meant as a compliment) who will share their knowledge... kind of like a car version of here...

Agree with others. Battery post connection might be loose or the actual cables could either be cracked or corroded. The same issue drove me batty for few days with my wife's old Odyssey. Good luck.

[saab2000]

Triple Ay is coming to the rescue.

I have the Plus membership, which once saved my butt about 22 years ago when the clutch cable on my VW Scirocco broke in Black River Falls, WI and they towed me to Eau Claire, WI for free. The tow cost more than the car was worth.

I tried to jump it with the neighbor and it made some noise for about 1 second and quit making that noise.

It will be towed a mechanic who has worked on it in the past and hopefully they can get it sorted out. If AAA can start it I'll drive it over there and leave it overnight.

I'm not a car mechanic and have very little knowledge of them. Thanks for the answers!

[brenick]

I once had a TR-7 with a dead battery problem. Turned out to be a low oil pressure indicator or some such problem activating a relay which drained the battery.

[ultraman6970]

Forums always have the right answers, check this forum out...

http://www.gminsidenews.com/forums/f31/battery-goes-dead-86315/

[Peter P.]

You better tell us what the mechanic finds!

Other causes: a glove box lamp or under hood lamp that intermittently is completing a circuit, lighting the lamp, and draining the battery.

A relay such as the A/C relay that is sticking closed when the key is off.

These are easy to measure if you know what the current drain is supposed to be when the vehicle is off. Many vehicles have computers which continue to run, and draw current, after the key is off. After a period of time these computers go to sleep and current draw drops to negligible levels.

For instance, Ford Crown Victorias draw somewhere in the range of 250mA, I think, when the engine is initially shut off. After 20 minutes it drops to 40mA. You can watch this happen with a voltmeter. If the numbers don't meet spec, there's something drawing excessive current.

Any aftermarket items installed on the Yukon like an alarm system or remote starter?

I also agree to have the battery tested before proceeding further, just to prove out your battery doesn't have a bad cell.

[aramis]

Sounds like it's probably a bad main ground or positive wiring harness. Both can be bought new from GM for not too much money. Sometimes all it takes is sanding down the terminals/connections though. Sometimes a weak or bad battery can cause the symptoms you posted.

But also check the current draw when it's off like the post above to see if something is draining the battery.

[saab2000]

The AAA guy connected his portable jump battery and it fired right up. Charging well. Battery tested fine with his portable tester. Ran it for about 30 minutes.

Drove it to the mechanic and I'll be there at 0730 when they open.

No aftermarket accessories. We'll see....

[arcadian]

I once had some rodents chew some of the wiring harness. Very similar symptoms. Took a bit to find.