Unsolved Battery Drain (with detailed troubleshooting)

Easy Rider · Mar 12, 2014

srivenkat said: ↑

In any case, just to reiterate, please don't be hard on yourself .
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There was just a tiny bit of sarcasm in my previous post.

PriusGuy32 · Mar 12, 2014

Yawn. These discussions arent anywhere near as entertaining as the other automotive forums I frequent... nobody threatened a good ol' American nice person kicking at the next Prius meet or even made comments about an "internet armchair jockey" or whatever they say, lol

Step it up a notch guys, lets make this debate personal!!! haha jk!

Longinus876 · Jun 11, 2023

Auto Engineer said: ↑

Semi-long story.

Background:
Earlier this week I noticed that the doors were having trouble unlocking. It would go through five sets of double beeps trying to unlock the doors. About 25% of the time, one of the drivers door wouldn't unlock. Odd I thought, did some searching and found that the Prius lock actuators appear to fail over time (see: Fixed: Door Lock Actuator in Gen II Prius | PriusChat). Others suggested 12V auxiliary battery issues. I just replaced the stock 12V with an Exide AGM FP-AGM51JIS in March (~6 months ago), so I assumed it wasn't the aux battery. I thought I'd dig into the locks further this weekend.

Today, when I attempted to start the car after work, I got the red exclamation light. I checked my ScanGuage and noticed the voltage was 9V. Odd, I thought as it always reads 12.X volts after sitting for hours. I shut the car off and restarted. Somehow it mustered enough power to kick on the electronics and start the engine. I drove home to get tools.

Troubleshooting:
My thoughts are either (1) that my battery has an internal short or (2) my car has an external short somewhere. I disconnected the negative battery cable and measured the current (car fully off, all dome lights off, ScanGuage disconnected). The measurement was 1.5-1.6A. This seems really high I thought. I did some searching on PC and found reports of the JBL amp being stuck on and drawing high current (see: Auxiliary battery keeps dying | PriusChat). I pulled the audio and amp fuses. No luck, still the same current draw. So I meticulously pulled each fuse in the driver's side foot well (2-3 at a time) and tested. Again no luck, same current draw. Also pulled all the fuses and relays (2-3 at a time) in the fuse box under the hood. Still no luck, same current draw. I did not pull the 30-100A fuses that are all tied together.

Battery voltage during the testing was between 10.7V and 11V. After some time testing, the current draw dropped from 1.5A to 1.0A, but this appeared to not be related to fuses, as it couldn't be repeated with the same circumstances. Regardless 1.0A seems very high. Others (such as Patrick Wong) report the "power-off draw" to be 20-50 mA. I assume these are utilizing the same method that I described via the battery ground.

My expensive multimeter won't power on (not the battery...ugh another issue). But I measured the current with two inexpensive Harbor Freight-style multimeters. Both measured the same current.

Also, no check engine light on the dash and no diagnostic trouble codes are reported by the ScanGauge.

Questions:
What am I missing? Are there any other fuses or relays to check? I would assume all relays are fuse protected.

What else could cause this large current reading? Does the car register a lengthy current spike for sometime when reconnecting the battery? I measured the current for up to 30 seconds when "completing the ground circuit" via the multimeter and the current seemed consistent.

I left the negative battery disconnected to prevent further battery drain and battery degradation.

If the battery truly is draining at 1.0-1.5A, it would drain 12-18 Ah when sitting overnight, which is probably consistent with dropping from 12V to 9-10V. The battery is reportedly 45 Ah.

Thanks to all for any guidance.
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What did it turn out to be???

Brian1954 · Jun 12, 2023

Longinus876 said: ↑

What did it turn out to be???
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He replaced the 12v battery. See post #14 above.

Why do you keep asking this same question in old threads? You need to continue with the thread that you created for your 12v battery problem, https://priuschat.com/index.php?threads/241010/

Posted via the PriusChat mobile app.

Unsolved Battery Drain (with detailed troubleshooting)

Easy Rider Active Member

PriusGuy32 Prius Driver Extraordinaire

Longinus876 Junior Member

Brian1954 Active Member

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Unsolved Battery Drain (with detailed troubleshooting)

Easy Rider Active Member

PriusGuy32 Prius Driver Extraordinaire

Longinus876 Junior Member

Brian1954 Active Member