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I have a 2005 Corolla CE with manual transmission. About one month ago the car would not start, and the battery was discharged to about 8.5V. Car had been not running for a couple of days but nothing was left on.

Since the battery was under warranty, I replaced it. Charging system is OK (about 14V, and this problem only happens when the car sits for a couple of days).

The only issue I noticed was that the radio stayed on when the ignition was off (though the clock display did go out), but maybe it is not related. Anyway I turned off the radio.

For about 2 weeks all was well, every day or two I checked the battery voltage and it was OK.

Then a couple of days ago it was discharged again (about 8.5V). So first I charged the battery and the voltage has remained about 12.7V with nothing connected.

So it seems like some intermittent electrical drain is happening. A couple of times when I connect an ammeter in line with the battery (with everything off), the current measures about .2 amp. But a couple of other times .7 amp. However I don't know if this kind of checking has any validity.

So I am looking for some way to find out what is happening (since it is intermittent), or if there are any known problems like this. I might pull the audio system fuse in case it is involved (it is a stock system) but that is all I figured so far.

And if checking the current at the battery is valid, can I use this to try to find the problem?

3

I've seen where mis-adjusted trunk light switches cause the light to stay on with the trunk closed and then the battery drains. If you have fold-down rear seats this is easy to check. Otherwise you may need to enlist a small fearless helper or a video camera. Or just remove the bulb and see if the problem goes away.

  • This is a great idea, since you would not see it if it stayed on. I removed the bulb and we'll see. – user3169 Jan 31 '16 at 5:52
  • A month later and still OK. – user3169 Feb 26 '16 at 22:41
  • Three years later and still OK. – user3169 Mar 20 at 17:10
5

Checking the Key Off amperage draw is the standard test for this symptom. An ammeter that is very accurate in the Milliamp range is needed. Low quality meters are readily available and can quickly lead one to a false conclusion.

The test: Remove ignition key, wrap in aluminum foil if Smart Key, Wait at least five minutes, newer smarter cars will need longer to fully turn off all the computers. Some up to 1/2 hour. Note that some vehicles turn back on after 5 hours to test the evaporative system for leaks. Most vehicles draw a small amount of power when off. Almost all will draw less than 50 Milliamps.

Tools vary from inline types to inductive clamp over the wire models.

  • Are there clamp meters that are accurate in the low milliamp range? I figured this would require an inline meter, but I haven't really shopped around lately. – JPhi1618 Jan 29 '16 at 16:25
  • Yes, I use an Electronic Specialties model 688 that I got at Aeswave.com It is accurate enough for draw measurements. Lab type accuracy would require a good inline unit, such as a Fluke brand. – Fred Wilson Jan 29 '16 at 22:43
  • As a side note don't confuse milliamp probe with low amp probe. MIlliamp probes are very expensive and are generally used on cars for afr sensor testing. – Ben Jan 29 '16 at 23:41
  • I'm using a reasonably accurate digital multimeter inline. A clamp meter would be great but I think it is too expensive for one time use. – user3169 Jan 31 '16 at 5:56
  • @user3169 accuracy only needs to be in the 10 or 20 mA range. Good readings will be under 50 and the usual bad readings are over 200. – Fred Wilson Jan 31 '16 at 6:26
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The classic way to test this is to use the ammeter as you already have.

  1. Connect ammeter and get a base reading.
  2. Disconnect ammeter.
  3. Go to the fuse box and remove a fuse
  4. take a reading with the ammeter again to see if there was a drop
  5. repeat 2-4 until you find what is drawing the power

The radio staying on is a red flag for me. Is this the stock radio or an aftermarket? If it is aftermarket, I believe someone wired it incorrectly. If it is OEM, I believe it is either failing, or there is a short somewhere, possibly in the ignition switch. Do you have anything connected in your lighter outlet? If the radio is on, this might be powered also.

I am trying to think of what else might be on the accessory circuit that you could test, but nothing is coming to mind other than the radio and cig lighter at the moment.

  • I will try to narrow it down but it is intermittent. Today current (with everything off), is about 160mA. At least today the battery voltage did not drop. As for the radio, the fuse for the radio is under the dash above the pedals, and is not readily visible. My assumption is that there is only one accessory power line at the ignition switch, in which case the radio itself might have a problem. – user3169 Jan 31 '16 at 5:49

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