Polemic 1 Report post Posted January 5, 2022 So after totalling my beloved and reliable 2001 330Ci, I've bought a 2009 525i. The onboard computer shows nothing amiss beyond being overdue for a service (which has actually been done but my mechanic couldn't reset it). Today, the check engine light came on. I assumed it was complaining about what it saw as an overdue service. But out of curiosity I ran the OBDC I have over it, and got more codes than Alan Turing at Bletchley Park. These include (some codes may be wrong as my photos of the screen have reflections): 93FB - control-module fault 9408 - undervoltage during self test A3B1 - signal or value below threshold A559 - Supply was switched off (terminal 30G - f) A2CD - control unit undervoltage A46D MOST - ring reset fault 5B69 - wheel speed sensor rear axle: mixed up (!!) SF4B - Interface, instrument cluster 5DCF - Control module, under-voltage 5F45 - brake fluid level too low (this was topped up during the service just before Christmas) 6140 - redundancy comparison, driver's steering angle A830 - resetting system faulty A83B - Undervoltage 93D0 - Undervoltage A409 - Undervoltage 931D - System voltage When the car was trucked from Auckland to Wellington it took so long the battery went flat. I therefore invested in a new one from the AA at over $750 (on top of several thousand $ getting my dad's old car going as a back-up for the family and for sentimental reasons, plus of course the purchase price, all right before Christmas) 😬 So the multiple undervoltage faults can't be traced back to the battery. So my questions to the brains on this forum are: What's the possible cause(s) of the undervoltage reading? Could undervoltage be causing all, or at least some, of the other faults to show up? Why is the onboard computer showing everything okay other than oil and brake fluid? Obviously I'll double check the brake fluid visually, but aside from that is there anything here that's absolutely dire and could affect the safe operation of the vehicle or damage it if not addressed immediately? Quote Share this post Link to post Share on other sites
aja540i 1906 Report post Posted January 5, 2022 The undervoltage codes are almost certainly because the battery is low, thats what that means, just because it is new doesn't mean it is full!! A low battery can cause all sorts of codes in these, the problem will be figuring out what is sucking all the power out of the battery, I am going through a similar issue with my M5 at the moment, I keep a trickle charger on it all the time otherwise it won't start after a few days, and it had a new battery in November! Contnental cars kept it overnight and did an energy diagnostic but didn't come up with anything concrete so I am still trying to figure it out.... 1 Quote Share this post Link to post Share on other sites
KwS 2425 Report post Posted January 5, 2022 8 minutes ago, Polemic said: So the multiple undervoltage faults can't be traced back to the battery. They absolutely can, especially if they are historic codes. Being a 2009, i presume its an E60, in which case was the new battery correctly coded to the car? Clear the codes, drive it a bit, and see what comes back. Quote Share this post Link to post Share on other sites
Polemic 1 Report post Posted January 5, 2022 Just now, KwS said: Being a 2009, i presume its an E60, in which case was the new battery correctly coded to the car? Yes, an E60. Well the AA guy said it was coded correctly, but then again, he didn't seem too sure. Quote Clear the codes, drive it a bit, and see what comes back. I will try that tomorrow, thank you 👍 Quote Share this post Link to post Share on other sites
Polemic 1 Report post Posted January 11, 2022 (edited) Thanks KwS, I cleared the codes on the 8th and have been driving it for three days (I work from home so generally don't go far, so wanted to get some kms on it). Most of the codes have remained clear. Two, however, have recurred late today (the 11th), relating to the VANOS system, so I'm assuming they're probably for real. I'm still not sure if the battery was correctly coded to the car, though. That doesn't seem to be something the OBD reader checks for? However the lack of undervoltage faults leave me optimistic that it's okay, one way or the other. Edited January 11, 2022 by Polemic Quote Share this post Link to post Share on other sites
