Cars and electricity

About 4 months ago we got a new battery for our 2007 Honda Odyssey. Three times before today when I went to start it, while it started right up the radio and gps both wanted their codes, so something went dead sometime between the prior turning off the key and now. Today, it just was dead. No start, no lights, no door opening, but when I jump started the car it started right up and is currently planning what to do to us next in the garage. Any idea of a place to look for the answer? Sound familiar? Might OBDCII help.

Have your alternator tested, or just replace it.
It could be a worn belt, but I doubt it.
My money is on an alternator that has burned through the brushes.
It’s not an expensive repair: a few hundred dollars.

Sent from my adequate mobile device using Tapatalk.

check your battery cables. A loose or corroded connection- either at the battery, or the ground strap to the body- can cause these symptoms.

It could be dead because the alternator isn’t charging the battery. That could be a bad alternator (which might even be intermittent) or it could be a wiring problem of some sort or a bad connection.

It could also be dead because something isn’t switching off when it should and it’s draining the battery even though everything is supposed to be off. This can be something like a sticky relay or it could be something electronic in the vehicle failing and drawing power when it shouldn’t.

Our old Caravan would drain the battery if the rear door wasn’t shut properly. The switch for the dome light wouldn’t fully engage and it would leave the dome light on, killing the battery overnight.

I don’t know if every vehicle has it, but I know at least some of them will register an ODB-II code for low charging voltage. This doesn’t tell you if the problem is actually the alternator or the battery or the wiring, but if you are getting that code then you can at least narrow it down to the charging system and not something draining the battery.

OBDII captured no codes.

This is a very intermittent problem. Is there any way to track it down when there is no drain? Unfortunately it seems to me the answer is no. I remember around 15 years ago the same thing happened with an old car I had. I asked my FIL, who was a master mechanic and his only recommendation was to disconnect the battery. Since electronics have advanced quite a bit, I am a little hopeful that there may be a different solution these days.

First law of automotive electrical issues. Check the battery.

Unless you can read the date on the receipt for when it was bought, check the date code on the battery. It is embossed-stamped in characters about 1/8" in height or so, usually on the top or side, or on the positive terminal. Usually a three or four digit number, with a letter for the month (A=Jan, B=Feb, etc…) and a number (last digit of the year). It may be in a DDMMYY format using all numerals. This is the manufacture date of the battery. There may also be a sticker or ink stamp on the top of the battery with the ship date of the battery, with the same letter-number code as mentioned above.

If the battery is more than 3 years old, either have it checked by a shop, or just replace it. The majority of times, a new battery will fix most problems. You cannot properly diagnose an electrical problem with a bad battery. Batteries can seem fine, but die overnight.

If the battery is less than 3 years old, charge it overnight (or longer) with a battery charger.

Note: If you replace the battery with a new one, charge it before you install it. New batteries, on the average, are only about 75% charged when brand new.

When you have a fully-charged, known-to-be-good battery, start the vehicle and look at the battery gauge (volts or amps) on the dash. If you don’t have either a volt or amp gauge on the dash, shame on you for not having bought a vehicle with proper gauges. On checking with Google, it would seem that Honda Odyssey’s do not come with proper gauges. You can buy a digital voltmeter gauge that plugs into your cigarette lighter socket on eBay pretty cheap. They are very handy things to have.

After starting, the ammeter should be showing charging and/or the volt meter should be showing about 14 V. If the ammeter does not show charging, or you show less than 13V on the voltmeter, your alternator is probably bad. I doubt that is the case in your situation since 1) Honda alternators are nearly bulletproof, 2) a bad alternator will usually show signs of a weak battery (dragging starter, dimming lights at idle, car stalling at idle) and 3) the battery light on your dash would have lit up.

If diagnosing the problem with a voltmeter is not in your skillset, you are probably better off taking the vehicle to a mechanic to do it for you. He will probably want to sell you a new battery if it is more than 3 years old. If the battery is less than 3 YO, he will probably charge it overnight before checking things out.

Usually, it is the battery.

Thanks for the great advice. When my five year old battery died about 4 months ago I just bought a new one without questioning anything. This battery is about 4 months old, and I also have the weird intermittent problem of evidence that it had momentarily died as a couple of times in the last few months I had to punch in the code to the nav system even though the car started up right away. I will pick up a plug in ammeter/voltmeter and see if it tells me anything.

Have the symptoms you’ve described only appeared since the battery replacement? If so, carefully check any connections that were disturbed in changing the battery. If the connections are good, I’d say you have a faulty battery, probably with an internal fault that may or may not show up during testing – which I bring up because you may not get warranty coverage unless the battery vendor can detect the fault. But whether or not you have to pay for it, you probably really want a new battery for reliability.

My wife’s Jeep developed a similar behavior a few years ago. We eliminated the battery and the alternator as causes, but the problem remained. And was frustratingly intermittent. But was getting worse = more frequent as time went on.

Turned out to be a bad electronics module. When you park the car and hop out the dome lights turn on. And remain on for a couple minutes then very prettily fade to black. At least that’s what happens when the module is working right.

When it’s working wrong, the dome lights turn themselves on for awhile at random. Or simply stay on after you walk away. We finally caught it when I went out in the garage at bedtime to empty the clothes dryer and saw the dome lights were on. Further investigation showed all doors fully closed and the interior dome light switch was not on. I cycled the driver door and the lights dimmed properly after a couple minutes.

I got up and checked in the middle of the night for the next week. The lights were on 4 times.

Armed with that knowledge the dealer replaced that module for very little labor. Absent me catching the car acting up in that specific way they would have been on a hopeless voyage of guesswork through a complex mass of computers and semi-smart modules. A voyage powered by great mounds of my money.
With luck you can catch the alternator red-handed with your new plug-in voltmeter. Absent that, start checking on the car at night when you can see any interior or exterior lights or vid screens without touching it or opening any doors. Failing that, start saving up for that voyage of discovery. Or sell the haunted bitch to somebody else & get another one.

A search on websites dedicated to Odyssey owners might have info about some specific queertron your model is prone to.

Wait a second here. I forgot all about the weird dome light goings on. Very rarely they will not turn off, and it is hard to tell but I think they sometimes just turn on by themselves.

Also, this started a month or so before we replaced the battery, but happened immediately after we had the brakes redone. Like the very next day. I was going with correlation does not imply causation but do you think it is possible to do something with the brakes that could cause this weird problem?

The brakes wouldn’t have anything at all to do with it; the dome light on the other hand is an extremely probable cause.

I would check the grounding. This sounds like a grounding problem