GS Fault Memory Lock Undervoltage

I have indeed seen similar issues on the Lexus GS platform. The fault memory lock being active, coupled with a stored error and your suspicion of undervoltage, certainly points towards a power-related anomaly within the vehicle's electrical system. Have you checked the battery's condition and the charging system output recently? Also, which specific ECU is reporting the error?

Thanks for the quick reply. I haven't had a chance to delve too deeply yet, but I did a quick multimeter test on the battery and it seemed within normal range. By ECU, do you mean the hybrid control unit? Or are you thinking something more like the engine management?

Yes, my apologies for not being more specific. While the hybrid control unit is certainly a possibility, I was primarily thinking of the engine management ECU or potentially the body control module. Given the undervoltage suspicion, a thorough diagnostic scan with a capable scan tool is recommended to pinpoint the precise ECU and fault code. Based on the information you've provided, I recommend a workshop visit to perform these tasks with specialized equipment.

Understood. Thanks for confirming my suspicions and clarifying the likely culprits. I'll take it into a workshop and have them run a full diagnostic. It turned out to be a faulty voltage regulator, costing around 240€. Thanks again for your help!