Electrical Drain

[birdman]

My 08 LB has gone through 2 new batteries in the past 3 weeks. This last battery went completely dead. Something is draining the battery while it sits in the garage with only the security alarm on. There are no interior lights or external lights left on. Anyone have a clue as to what could be the cause?

[goku87]

Had the same thing with mine. Took it to the dealer, told them to fix it. Apparently a faulty ECU can drain a battery, and they wanted me to pay about $360 or so for repairs.

I had a nice chat with the lead mechanic.
Warranties are awesome.

Me: 1 Stealership: 0

[CTScott]

If you have access to a multimeter, you can check the powered off current drain yourself. This is from a post I made in another thread a couple of months ago:


On my 09, which has keyless entry and remote start, I measured the off state current draw at approximately 300mA. This means that in 24 hours this powered off Yaris will use 7.2 Amp Hours. This is a significant amount of draw, as it means that this sitting Yaris will have a dead battery in less than two weeks.

On Crashy, who is a bare bones 08, I measured the off state current draw at approximately 160mA, which equates to 3.84 Amp Hours of draw in 24 hours.

In doing some measuring of current draw of various things while the ignition is off I found the following to have the most significant draw while powered off:

ECM: 50mA
Body ECU: 100mA
Radio: 5mA
Clock: 5mA
Keyless Entry/Remote Starter on my 09: 150mA


The ECM, radio, and clock are all reasonable. The keyless entry / remote starter on my 09 is no surprise as it is an active system waiting to hear from an RF remote. The body ECU is the one that really surprises me. This is an ECU that is built into the white plastic chunk that we tend to refer to as the under dash fuse panel.

[firebob]

Keyless Entry/Remote Starter on my 09: 150mA


I need some help understanding why crashy needs keyless entry or remote start. I’m sure it was a nice to have at one point.

[CTScott]

I need some help understanding why crashy needs keyless entry or remote start. I’m sure it was a nice to have at one point.


LOL... Crashy is a bare bones 08. My 09 is the one with the keyless and remote start.

[firebob]

LOL... Crashy is a bare bones 08. My 09 is the one with the keyless and remote start.

Ok that’s good. I had something messed up.

[talnlnky]

yeah... with a multimeter make sure all lights are off, and the car is off.

Disconnect the negative terminal on the battery, then set your multimeter to milliamps and use the multimeter probe to bridge the electrical gap between the battery post, and the terminal cable.

What this does is allow the multimeter to see all the current that is being drawn. From here you can get a baseline of the amp draw. When you first hook it up the computers will pull power, but after about 15 seconds I'd imagine they should start going into a low power/sleep mode. Haven't tested the yaris so don't know what the power drain should be like.

once you have your baseline reading.... disconnect the meter, and then pull a fuse, and retest. You are looking for which circuit the drain is on.

once you find the circuit... then you can look at wiring diagrams and trace the problem more effectively.

I did this last summer with my fiancee's 93 chevy truck. had a .9amp draw... turned out to be about .3amp dome light issue... and .6amp heater/AC box issue... since the truck is used only to haul hay & horses we opted to just yank the heater controls and the dome light fuse... all is fine with the truck now. The normal current draw on the truck is like 6mA I believe.

[birdman]

The weird thing is that my first battery lasted 16k miles while the second lasted 3 weeks. What ever it was that started malfunctioning started well after I bought the car.
The dealer says they have done all they can and cant find the cause of the problem. Could it be a failure of the diode bridge or voltage regulator in the alternator that causes it to intermitantly stop charging?

[CTScott]

The weird thing is that my first battery lasted 16k miles while the second lasted 3 weeks. What ever it was that started malfunctioning started well after I bought the car.
The dealer says they have done all they can and cant find the cause of the problem. Could it be a failure of the diode bridge or voltage regulator in the alternator that causes it to intermitantly stop charging?

I think the key is to first figure out if the issue is lack of charging or excessive "off" current draw. The charging one can easily be checked out by measuring the battery voltage while the car is running. If it is greater than the voltage when the car is off (and is fairly steady {i.e. not bouncing from 12 to 15 volts}) then your charging side is probably fine.

[birdman]

I called the Dealership Service Manager just now and read him the comments on this thread and he said his technician performed the same ones without finding anything out of place. He agrees that something is wrong but doesn't know how to find the little gremlin. He's going to discuss it with a Toyota tech advisor. Thanks to everyone for their ideas on this problem. I will let you know how this plays out.

[goku87]

I called the Dealership Service Manager just now and read him the comments on this thread and he said his technician performed the same ones without finding anything out of place. He agrees that something is wrong but doesn't know how to find the little gremlin. He's going to discuss it with a Toyota tech advisor. Thanks to everyone for their ideas on this problem. I will let you know how this plays out.

That's really weird, because they told me the same thing the first time I took mine in too...

[talnlnky]

The weird thing is that my first battery lasted 16k miles while the second lasted 3 weeks. What ever it was that started malfunctioning started well after I bought the car.
The dealer says they have done all they can and cant find the cause of the problem. Could it be a failure of the diode bridge or voltage regulator in the alternator that causes it to intermitantly stop charging?

yeah... that's possible... but on a new car.... electronics rarely are deffective like that... possible tho..

[talnlnky]

I think the key is to first figure out if the issue is lack of charging or excessive "off" current draw. The charging one can easily be checked out by measuring the battery voltage while the car is running. If it is greater than the voltage when the car is off (and is fairly steady {i.e. not bouncing from 12 to 15 volts}) then your charging side is probably fine.

agreed... without the clamp meter/ammeter tho even a voltage reading of 14.xx doesn't say for sure if the charging is fine.... do toyota shops even carry clamp meters tho?

OP: have you done any mods to the car... anything in which you may have disrupted some wires (such as HID's, stereo, or anything under the dash)?