Lexus IS Additional Battery Alarm Error

I've got a 2013 Lexus IS with a gasoline engine and about 62,000 km on it. Recently, I've been getting an error related to the additional battery alarm system. Basically, it's defective, and the car alarm isn't working at all. The error memory stores a fault. Any ideas what might be causing this?

4 comment(s)

Sounds like a classic case of a weak auxiliary battery. These systems are sensitive to voltage drops. Has the battery ever been replaced? Before diving into anything complex, I'd suggest a simple battery check.

Thanks for the quick reply! No, I haven't replaced it yet. Is there a specific way to test it, or should I just measure the voltage?

Just measuring the voltage isn't always enough, as it may appear okay without a load. If you are not familiar with this, the best is to go to a workshop, they can do a proper load test. From what you describe, it's very likely that a discharged auxiliary battery is the reason for this. The repair including system diagnosis was around 330€ for me.

Okay, thanks for the advice! I'll take it to a workshop and have them run a load test on the battery and check the system diagnosis. Hopefully, that resolves it. I will let you know how it goes.

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