[dlindqui]

Hello,
I had been having battery issues so I took my 2021 Corolla to the dealership and had them do the recommended diagnostics on the battery, starter, alternator, and check for parasitic draws. The dealership said that it was a battery issue and that the battery was so low that they couldn’t test the alternator. They wanted $290 for the battery replacement when the battery was $180 so I decided to just buy it and replace it on my own. I bought a multimeter and wanted to check for parasitic draw.

1. Could someone confirm that I am testing and reading this correctly? I followed the instruction booklet and waited 30 minutes for the car to be in sleep mode, put the black lead on COM and the red lead on 10A, set the multimeter setting to 10A, and connected the red lead to the negative cable and the black lead to the negative post. With those settings I got readings mostly between 0.35-0.45 which I believe is between 350-450 milli amps and way above the 50 milli amp expected limit. When I started to pull fuses I pulled the J/B-B and VVT fuse and it dropped down to 0.19. When I plugged the fuse back in it rose to 0.27. But those levels are still way over what it’s supposed to be.

Second, I was looking at the fuse diagram and I don’t have all of the fuses/relays in the diagram. Is it possible that I’m missing fuses/relays or are those likely for options/configurations that I don’t have?

Thank you so much in advance!

 

[PJTruslow]

for parasitic draw tests, you really need them to be connected the whole time for the car to definitely be asleep. you should give it lots of time if you just connected the multimeter (and everything lost power while you were setting it up).
by my napkin math, 200mA should consume about 5Ah per day.it would take about a week for that to deeply discharge your car battery and it's low enough that 24 hours should be fine. if you drive the car daily and it is never idle for more than two days like mine is, it probably wasn't the issue but if it really is 200mA, that seems like too much.

 

[Gugi53]

Change the meter you have to 20V, and continue volts. Check the battery voltage. Start the engine and check the volts again from the battery. Posted the results here.

Hello,
I had been having battery issues so I took my 2021 Corolla to the dealership and had them do the recommended diagnostics on the battery, starter, alternator, and check for parasitic draws. The dealership said that it was a battery issue and that the battery was so low that they couldn’t test the alternator. They wanted $290 for the battery replacement when the battery was $180 so I decided to just buy it and replace it on my own. I bought a multimeter and wanted to check for parasitic draw.

1. Could someone confirm that I am testing and reading this correctly? I followed the instruction booklet and waited 30 minutes for the car to be in sleep mode, put the black lead on COM and the red lead on 10A, set the multimeter setting to 10A, and connected the red lead to the negative cable and the black lead to the negative post. With those settings I got readings mostly between 0.35-0.45 which I believe is between 350-450 milli amps and way above the 50 milli amp expected limit. When I started to pull fuses I pulled the J/B-B and VVT fuse and it dropped down to 0.19. When I plugged the fuse back in it rose to 0.27. But those levels are still way over what it’s supposed to be.

Second, I was looking at the fuse diagram and I don’t have all of the fuses/relays in the diagram. Is it possible that I’m missing fuses/relays or are those likely for options/configurations that I don’t have?

Thank you so much in advance!



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[peng]

PJ's right - as soon as you remove the clamp, everything loses power. When you connect the multi-meter, everything powers up and current draw will be high for quite some time.

What you want to do is find a way to permanently connect the multi-meter to the battery post and clamp and also put in a jumper between the battery post and clamp. Let it sit for a few hours, then power up the multi-meter and remove the jumper.

I just came back from a week's vacation and checked my battey when I got back. It was still at 85% capacity.

 

[PJTruslow]

What you want to do is find a way to permanently connect the multi-meter to the battery post and clamp and also put in a jumper between the battery post and clamp. Let it sit for a few hours, then power up the multi-meter and remove the jumper.

what OP could do is with two people, hold the multimeter probes in place while removing the ground. it would be tricky, but would allow you to get a reading without disturbing it.

 

[peng]

Or attach the red probe to any part of the engine block and hold the black probe on the negative battery post (under the clamp) then remove the clamp.

 

[Raithskar]

Automakers seem to go with barely-adequate batteries for newer vehicles, considering all the added tech-bloat & passive/parasitic draw they have nowadays. No doubt this allows them to cut their costs some more. So, it seems prudent to replace a regular factory/OEM battery with beefier quality AGM battery within 1-2 years of buying a new car these days, just to be safe & account for more variance in driving behaviors/frequency & environmental conditions.

 

[ohw]

While it is good to learning something new, but is your car still under warranty? If it is, check if the battery should be covered and let the dealer do all this fun stuff to find the draw.

 

[75aces]

Put amp clamp on positive battery wire. Wait around half hour after car tired off. If meter displays voltage or amps, something is still awake. Then go one by one until you find the big draw.

Cant leave amp clamp unattended. It will turn off on its own.

 

[jmoney1119]

For real, there’s a decent chance your battery might just be dead. My 2020 has to have its battery replaced a few months back, and I know quite a few others had some issues with the factory battery not lasting very long.

Checking for parasitic draws can a real big waste of time if you’re looking for something small. A lot of things in the car draw a small load when it is off.

 

[ken2116]

One can measure current draw at the fuses without disconnecting them, provided you have a sufficiently sensitive voltmeter. Each fuse has some resistance, which can be measured when the fuse is out of its socket. With the fuse back in place, measure the voltage across the fuse and calculate the current using Ohm's Law, Current (amps) = Voltage (vts) divided by Resistance (ohms).

Fuse resistances are small, to determine them accurately you might need to subtract the resistance of your meter's leads and probes (the reading when the probe tips are touched together) from the resistance measured when probing the fuse. There are other ways to accurately measure fuse resistances - a) if you have access to a 4 wire ohmmeter you're all set, or b) you can measure the voltage across a fuse while passing a known current through it and calculate the resistance using Ohm's Law.

You also can consider using a recording meter to monitor current draw over a longer period of time, such as overnight. I've used some very nice Fluke meters (high quality but $$$), and less expensive brands are available.

 

[BillDurham]

Remove a battery terminal, doesn't matter which one. Connect the end of a jumper wire to the battery post. Connect the other end of the jumper to the cable. Set your meter to milliamps. Connect a lead to the battery post, and one to the clamp. The meter is reading zero or nearly because the jumper is carrying the current. After an hour disconnect the jumper. The jumper has kept the car alive long enough for everyone to go to sleep. Now read the current. From an old mechanic who fixed stuff like this that four other dealers couldn't.

 

[ken2116]

Remove a battery terminal, doesn't matter which one. Connect the end of a jumper wire to the battery post. Connect the other end of the jumper to the cable. Set your meter to milliamps. Connect a lead to the battery post, and one to the clamp. The meter is reading zero or nearly because the jumper is carrying the current. After an hour disconnect the jumper. The jumper has kept the car alive long enough for everyone to go to sleep. Now read the current. From an old mechanic who fixed stuff like this that four other dealers couldn't.

That should work, but in the event the op is using an old style meter (or maybe a very cheap one) it's better to start with a high current range setting (to avoid blasting the meter with a large off scale current) and then working down to the appropriate range. This might not be a problem with a good DVM.

Another caution: when configured to measure current the meter is essentially a short circuit. it's essential to switch the probes back to the voltage measuring position before connecting them across a voltage, example: measuring the battery voltage. It's easy to overlook this and it's wrecked more than one meter.

 

[PJTruslow]

Remove a battery terminal, doesn't matter which one.

It doesn't, but I would always advise the negative. if you wrench contacts the frame when working on the negative terminal, nothing happens. if your wrench touches the frame while working on the positive, you short out the battery and at best leave scorch marks, at worst you have a fire. my rule of thumb is never put a wrench on anything positive until the negative battery terminal is disconnected.