I have swapped out the USB cable, the USB adapter, as well as had the socket tested by volt-meter at the mechanic. Everything checks out as normal.

The "charging" icon shows up on phone display, but percent charged goes down from 30% to 29% after about 45 minutes of charging!!!

Any ideas?

[From the comments] The phone charges correctly in other vehicles.

  • 2
    GPS, WiFi, etc. were all turned off. A special, 2.1A adapter was also tested with this 2007 Yaris, and 2.1 amps is kinda difficult to outrun, if you know what I'm saying ... Dec 2, 2016 at 19:57
  • 1
    I think the OP is getting a hard time, the socket could show a voltage enough to fool the phone into thinking its charging. But there could be a bad connection or frayed wire limiting the current being supplied. Dec 2, 2016 at 21:30
  • I have a tablet that charges via USB, and it charges slower than it drains while in use. Turn the screen off for 10 minutes while charging and see if it up faster.
    – Criggie
    Dec 3, 2016 at 0:10
  • Given that your power adapter functions normally in other vehicles, this sounds like a problem with the cigarette lighter voltage sagging excessively under load, preventing the USB adapter from supplying adequate power to the phone. This would not be evident by simply using a voltmeter, which just measures the open-circuit voltage and does not put a meaningful load on the socket. (Consider that you're probably pulling at most 1.5 A when the fuse for the cigarette lighter socket on the Yaris is rated for 15 A; clearly, something is wrong with the socket.)
    – bwDraco
    Dec 3, 2016 at 4:10

4 Answers 4


You could have voltage at the socket with only one strand of copper connected so simply testing for voltage doesn't mean there isn't a fault.

How to check for a bad Ground:

  • Connect a load to the socket
  • Set the multimeter to measure voltage
  • Connect one lead to the Ground connection of the socket
  • Connect the other lead to a known good ground If the meter reads above one volt you have a bad ground.

How to check for a bad Positive:

  • Connect a load to the socket
  • Set the multimeter to measure voltage
  • Connect one lead to the Positive connection of the socket
  • Turn the ignition on
  • Connect the other lead to a known good Positive If the meter reads above one volt you have a bad positive connection.

You could perform a voltage drop test. If the voltage is reduced by the time it hits the phone, it might be high enough to trigger the charging indicator, but not actually be able to charge. Explanation of voltage drop test

  • Will ask the mechanic if he has the voltage drop tester. Thanks! Dec 2, 2016 at 20:04
  • Its not really a tester per se. You apply a load to the circuit, and take a volt meter and put both leads on the same side of the circuit at different points (both on positive and then both on negative). It is normal to see a small voltage indicated, but a large number would indicate there is some resistance in the circuit.
    – Mobius
    Dec 2, 2016 at 20:07

Just because you are getting voltage does not mean you are getting current. You may have a frayed connection or corrosion somewhere between the car battery and the cigarette lighter that reduces the amount of current delivered to the cigarette lighter.

Also check the fuse for the cigarette lighter port. Make sure it's good, properly seated and that there's no corrosion either on the fuse or in it's socket.

  • I asked a guy to check the fuse, and when I came back later, he told me he "accidentally blew the fuse" so he replaced it. Dec 2, 2016 at 20:48

Yiu can get a little inline meter that measures the particulars of the power drawn from the USB cord. If it’s simply not delivering the needed current, that will show.

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