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milaschulz1

Lexus IS Overvoltage Error

Hi, I have a 2008 Lexus IS diesel with 67147 km. I'm getting an overvoltage error, causing a cascade of problems. The fault memory is full of overvoltage entries, some systems are failing, and the battery seems weak when starting. Could this be an alternator issue or something more sinister with the car's ECU?

4 comment(s)

gabrieleagle70

I had a similar issue with my IS. Overvoltage can be tricky. Have you checked the battery itself? A heavily discharged or defective battery can sometimes cause the alternator to overcompensate, leading to overvoltage. It's like a dam that's suddenly breached; the system gets overwhelmed. Also, what's the measured voltage at the battery when the car is running?

milaschulz1 (Author)

Thanks for the reply. I haven't load-tested the battery yet, but I'll add it to the list. I don't have a multimeter to check the voltage when the car is running, but I can probably borrow one. If the battery checks out, what else should I be looking at?

gabrieleagle70

If the battery is fine, then the alternator is the next most likely culprit. The voltage regulator within the alternator might be faulty, causing it to output too much voltage. It could also be a wiring issue, but those are less common. Given the symptoms, I'd suggest getting it checked by a workshop with proper diagnostic tools. Running with overvoltage can damage sensitive electronics, like the ECU. Think of it as feeding your computer with too much power – not a good outcome.

milaschulz1 (Author)

Thanks for the advice. I took it to a workshop, and you were spot on. It was indeed the battery being heavily discharged, which led to the alternator running at full capacity. New battery and fitting cost me 290€. Appreciate the help!

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