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Thread: Car keeps losing charge seemingly randomly with new FSR and voltage regulator

  1. #1
    Join Date
    Nov 2016
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    Angry Car keeps losing charge seemingly randomly with new FSR and voltage regulator

    Experiencing some wild issues when it comes to my battery. Here's my quick history. Three times in the last 60 days, my battery has depleted so low that I was unable to start the car. The first time I thought it was a fluke, and the second time I decided to do something about it. I bought a new FSR (Rein from FCP), new Voltage Regulator and a new-to-me HVAC control unit. March 30th I drove to work and turned off my car, to find the HVAC still on. I could even completely lock my car and unlock my car and the HVAC control panel stayed on until I unplugged my battery.

    Some time in the last 7 days, my HVAC unit randomly changed to Celsius. No amount of driving, on-off cycling or deep sleep states corrected this behavior. Saturday I was unable to use my HVAC controls at all, a previous symptom I have experienced. I got home, unplugged the battery, reconnect it, and my HVAC has returned to Fahrenheit and now turned on.

    Sunday came around and I was growing concerned. In the middle of day, my battery is reported 12.4V according to my radar, tapped into the power of my mirror. Monday morning came along and the car unlocked, but refused to crank at all. Radar reported 9.4V. I disconnected the battery. When I got home from work in another vehicle, the battery was reporting 10.8V. Seeing that, I went to get my battery charged back up to 12.4V. I left it unplugged overnight, drove it to work today (Tuesday), unplugged it at work, and then got the battery tested. Previously they would indicate to me the battery is healthy but needs charge, however this time they said it seemed charge. Today I got home and it reported 12.2V.

    I want to believe that the battery issue is unrelated to the HVAC system, but the fact that the HVAC stayed on after I turned the car off even with a new FSR leads me to believe its still an issue in this system. I went just went down to the car for this post. The voltage is 12.2V right now, and I have a shadow code in the HVAC for "Auxillary heater Relay" aka the K4 relay. I want to believe the relay is sticky, but that would be just for the heater as far as I can see, not for the entire climate control panel. This thread seems to believe otherwise. PN is 61 36 8 373 700. I'm not sure what to do from here, but any advice is appreciated.

    Edit: The wiring diagram does imply that power predominately comes through fuse 37, 28 with the latter also powering the FSU.

    edit 2: except for the 30 seconds of running right after the freshly charged battery was in, the car is stuck at 13.5V when running regardless of battery charge state.
    Last edited by YoitsTmac; 04-07-2021 at 01:38 AM.

  2. #2
    Join Date
    Jul 2016
    Location
    Austin Texas
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    235
    Tons of variables. Isolating the short/drain to a single circuit will help you preserve your sanity. Do you have access to a multimeter with a current clamp? They're quite cheap off Amazon and very handy because they'll accurately measure the current off your battery without having to string it in series. Then it's mostly a game of pulling fuses and watching to see when the current draw drops.

    Also make sure your car is going to sleep. After 16 mins all interior lights should be off and the VA line out of your gmm5 should be low.
    2005 Jet Black ZHP Sedan "Adriana" || TunedByDaniel || BMW Alarm + Fuel Lock || ORION V4s || Eagle Eyes || 435i Coupe Sport Seats || Perforated Leather X5 M-Sport Wheel || FLOW Designs Lip

  3. #3
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    Bought a multimeter and it should be here tomorrow. Car does seem to be going into sleep as far as I can tell. I left my car plugged in all last night and while at work with seemingly no drain. I again went to get my battery checked and on my way there, I got the highest operating voltage I have seen since this issue: 14.0V. Of course when I got there they reported the battery was full. The battery tested as "good", however they did notice the voltage drop when I started was "much larger than it should be".

    I got home and installed the new battery that had arrived. When I went to install it however, I heard the electric fan running. Only noticed because of the absence of the noise as I unplugged the old battery. Perhaps the relay for the fan is bad and it can't turn itself off. I will now be more cogsinant of this and see if I see this behavior repeated. Otherwise, I assume the battery was weak and am expected an improvement in typical voltages with this new battery.

    I will still check for parasitic daw when I get the multimeter. If it is my electric fan though, I have to make sure its running when the car turns off, no? Basically just beat the sh*t out of the car and then immediately park it?
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  4. #4
    Join Date
    Jul 2016
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    Austin Texas
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    According to realoem, the relay behind the glove box is for the compressor, but it seems like it also controls the blower. It doesn't seem like there's more than one.

    The green relays can be swapped for ease of testing. Maybe swap A/C relay with horn relay?
    2005 Jet Black ZHP Sedan "Adriana" || TunedByDaniel || BMW Alarm + Fuel Lock || ORION V4s || Eagle Eyes || 435i Coupe Sport Seats || Perforated Leather X5 M-Sport Wheel || FLOW Designs Lip

  5. #5
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    Nov 2016
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    Well the plot thickens. No parasitic draw and the new battery is clearly fixing the issue. Apparently a battery isn't supposed to drop two volts on start, who would have thought!

    HVAC issues are persisting. the HVAC went dark again as in couldn't be awakened no matter what. I tried to read for codes on PA Soft and the HVAC wouldn't even show up. I pulled out my radio to check the connections, but everything was in there good. Weird. But if I unplug the battery super quickly and re-plug it in, it comes back to life no problem. AC instantly worked too, but I'm bad at the same issue where the auto recirculating air isn't working. I don't have codes for it, but now I think I should be checking out the AUC sensor. The fun continues. Especially since I can't recreate the issue on demand.
    | My YouTube Channel | Instagram|

    BMWCCA GGC: 530872
    "You canít connect the dots looking forward; you can only connect them looking backwards." - Steve Jobs

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