adrianschmitz1
Mirai weak battery flickering lights
Summary of the thread
A 2018 Toyota Mirai experienced weak battery performance and flickering lights at 134,598 km, suspected to be caused by a faulty battery sensor. The issue was characterized by normal voltage when off but fluctuating and dipping to 11V when running. This pointed to a defective voltage sensor misreporting the battery's health, affecting the charging system. A diagnostic check confirmed the defective sensor, which was replaced, resolving the issue.
Did this summary help you solve your problem?
4 comment(s)
adrianschmitz1 (community.author)
Voltage off is normal, around 12.6V. When running, it fluctuates, dipping as low as 11V at times. Does that match your Volvo experience?
rolandwilliams1
Yes, those voltage fluctuations sound exactly like what I experienced. That definitely points to either a failing battery or, more likely in your case given your suspicion, a defective voltage sensor that's misreporting the battery's health. Since the voltage drops significantly when the car is running, the alternator or regenerative braking system might not be charging the battery correctly due to bad sensor data. I recommend taking it to a trusted workshop for a diagnostic check. They can accurately determine if it's the sensor and prevent further problems.
adrianschmitz1 (community.author)
Thanks. Defective battery sensor confirmed by the shop. Repair cost 315€. Replaced and all good now.
rmh_community_comment_box_header
community_crosslink_scanner_headline
community_crosslink_scanner_intro
community_crosslink_scanner_title
community_crosslink_scanner_price
community_crosslink_rmh_headline
community_crosslink_rmh_intro
community_crosslink_rmh_title
community_crosslink_rmh_subtitle
community_crosslink_rmh_brand
TOYOTA
community_crosslink_rmh_model
MIRAI
rolandwilliams1
I had a similar issue with my 2016 Volvo XC90. The symptoms sound very familiar. 'Weak battery performance when starting' means the battery isn't holding its charge as it should, possibly due to sulfation or internal damage, but in your case, a faulty sensor could be giving a false reading. Similarly, 'flickering lights' often indicates an unstable voltage supply. Low voltage or fluctuating power can cause lights to flicker. Was the voltage regulator ruled out? Before anything else, you should check the battery voltage with a multimeter. What voltage are you getting when the car is off versus when it's running?