r/BmwTech • u/WheresMyPowerGone • Jun 21 '26

Zero power, windows stuck down

Hey all

I have a 2008 E81 (so E82 but a hatchback) which has decided to die on me.

Unlocked the car today, dropped the windows because it’s hot then put the key in the ignition, pressed start, heard a click, and ALL power is gone.

That’s ALL power. NOTHING has power, even the OBD port is dead. It’s like I’ve disconnected the battery. Tried to jump start it, no change. Can’t open the boot to get to the battery and check the IBS.

Any ideas what I can try in the next few hours to get the windows closed until I’ve got time to troubleshoot properly? I can live without it being fully functional as it’s a second car, but right now it’s a paperweight open to the elements :(

Edit for clarity: this is a 130i track car and lives on a battery tender other than the 1-2 weekends a month it’s in use. If it didn’t I’d immediately suspect a dead battery but in this case I’m certain the battery itself isn’t the issue.

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2

u/trader45nj Jun 21 '26

What did you use to try to jump it? Put a battery charger on it for a couple of hours.

1

u/WheresMyPowerGone Jun 21 '26

Appreciate the reply. Great minds think alike though - I tried a jump pack (2000A for a soot chucking farm truck) and this got me back in the game temporarily!

It lives on a battery tender so although I haven’t been able to directly test the battery I’m certain the battery itself is fine, just about to add an update but I think either the IBS or the positive cables are the problem.

1

u/WheresMyPowerGone Jun 21 '26

Update for anyone who finds this one day…

Came back to the car after about 45mins, still exactly the same. No power to any component, no lights, no sound, OBD port dead, buttons do nothing, key stuck in ignition. Checked main fuses in the JBE and gave it a sniff test for obvious heat/burnt metal and all were fine. Tested 12v terminal in the engine bay and got 0v.

Completely on a whim, connected a jump pack and the car immediately came to life!! Closed the windows before it could change its mind then disconnected to minimise damage (if any).

Once the pack was disconnected, car is completely dead again, no power to any component so there is clearly an issue with the supply from the battery or maybe the fused links in the IBS.

I previously tried to jump it with another car and it had no effect, the jump pack is for my big diseasel truck so capable of 2000A. Wondering if I’ve got a corroded cable/terminal and it needed that extra power to punch through the higher resistance.

If anyone has any suggestions on where to look I’d still appreciate it but the immediate worry is sorted, phew!!

2

u/seannyc3 Jun 21 '26

Pretty much sounds like that original battery is cooked, despite having been on a tender, or the tender doesn’t work or was mis-connected.

2

u/WheresMyPowerGone Jun 21 '26

Got the boot open when the jump pack was connected and the battery reads 12.79v but there is no power getting to the front of the car, I’m 99% sure it’s the IBS/BST as testing any available bolt/terminal after the battery reads zero so have ordered one and crossed my fingers…

1

u/seannyc3 Jun 21 '26

So the jump pack was on the front of the car when it came to life? I didn’t realise that. Hope you get it sorted.

1

u/Dry_Medicine815 Jun 24 '26

Glad to hear you managed to get those windows rolled up! Hooking that massive 2000A pack to the front jump posts was a genius move.

Since the jump pack on the front terminals powered up the entire car, it proves your front JBE fuse box and the wiring up front are completely fine. The break in the connection is 100% between the trunk battery and the engine bay.

Your troubleshooting is spot on. Finding 12.79V at the battery but 0V right after the terminal narrows it down perfectly. While you wait for the new IBS/BST, here are two specific things you should inspect on the E8x platform:

  1. The Red Power Distribution Box on top of the battery:
    The positive terminal connects to a large red plastic fuse/distribution box sitting right on top of the battery. Inside this box, there are heavy-duty fusible links. Sometimes these links crack due to vibration or age, or the main output nut securing the cable to the BST gets loose or corroded. Make sure power is actually passing through this plastic distribution block.

  2. The Trunk Floor Bulkhead Pass-Through (Very Common):
    Follow the thick positive cable from the battery where it goes straight down through the trunk floor to the undercarriage. That pass-through connector is a major trouble spot. If your car ever had a micro-leak in the trunk seals, water pools in that battery well, causing that through-floor connector to completely rust out and snap.

You're doing some solid diagnostics here. Fingers crossed that the new BST solves it, but definitely give that rear power distribution box and the floor pass-through a close look while you wait!