ludwigfischer94
S40 Battery Drain
Summary of the thread
A 2001 Volvo S40 diesel was experiencing battery drain issues, with symptoms including error messages, weak and flickering lights, and difficulty starting. Despite the alternator functioning correctly and no obvious parasitic draws, the problem persisted. It was suggested that a faulty battery sensor could be causing the issue by providing incorrect data to the car's computer, leading to improper battery management. Replacing the defective battery sensor resolved the problem.
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4 comment(s)
ludwigfischer94 (community.author)
I haven't done a load test yet, but the resting voltage seems normal, around 12.6V. When the engine is running, it's charging, showing about 14.2V. I'm wondering if a faulty battery sensor could be causing a phantom drain, even with the charging system appearing normal. Can a bad sensor really cause this kind of heavy discharge?
erikice1
Yes, a defective battery sensor on those models can absolutely cause a significant battery drain. The car's computer gets bad data and doesn't manage the charging properly. It's likely the culprit given your symptoms. Time to take it to a workshop.
ludwigfischer94 (community.author)
Thanks for confirming my suspicions! I took it to my local garage, and they confirmed the battery sensor was defective. Replaced it, and it's solved the problem. Total cost was 315€. Appreciate the help!
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VOLVO
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S40
erikice1
Sounds like a pain. Have you load tested the battery itself? What kind of voltage are you seeing across the terminals when the car is off, and then again while it's running?