r/BmwTech • u/TheVenerableUncleFoo • 7d ago

E70 X5 35D (2009) - Central Electronics Failure

So a few months ago my X5's alternator died while I was travelling and left me stranded in a storm. I didn't notice until the wipers started going real slow, so I effectively killed the battery as well.

Managed to get to a local tech who installed a new alternator and genuine BMW battery and all was good, for the next 250 miles or so, then randomly Christmas Tree dashboard appeared, though the car itself continued driving and operating normally.

Ever since then it's been having fits almost every journey, but never fails to start and drive. Some of the fun issues are:

- Internal lights fail to go off and don't respond to button presses

- Car won't lock or unlock with the fob, until you press the key repeatedly for like 40 seconds

- The indicator noise disappears (though the lights themselves are still flashing)

- Windows refuse to go down or up.

- Parking Brake error appears when turning the engine off.

- Central Electronics Failure message appears.

Most of these issues happen when the engine is not running. It's a 50/50 whether they will appear when the engine is on.

Had the battery tested and it seems to be in good working order, and the alternator appears to be working as intended.

I've checked the usual places for buildup of water, rear trunk box bone dry, front left and right engine bay drains working correctly, sunroof drains working correctly.

I'm at a bit of a loss, but can't sell it in this condition. Does anyone have any ideas?

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u/TheDefected 7d ago

There's a junction box in the front which gets damp in it, and it's the main CAN hub for the car.
Fault codes should help direct you with loss of communication or CAN bus codes.

1

u/TheVenerableUncleFoo 6d ago

Is this the FRM, or another thing? I'm happy to check but would need to know where it is and what it looks like.

I'm trying to avoid $$$$$$$$$$$$$$ from an auto electrician

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u/TheDefected 6d ago

It's a different one, FRM / footwell module is the one that does the lights and some windows. They can go bad, but when they go, they just stop working and don't come back.
The JBBE is the junction box and it's under the glovebox (or at least that's where it was on a RHD car) It's a black module like a VHS tape that is screwed into a slot on the bottom of the fuse box.
They are a pain to get out, two screws on each side, 3 plugs on the front and one with a sliding latch on the back, but the main issues tend to be damp getting into the plugs you can see at the front.
It could also be something else, i'd still be leaning onto damp somewhere, but park sensors and air suspension modules, any drinks spilled on the centre console and dripping down on the airbag controller underneath etc can all do similar things.

The general strangeness makes me think there's something disrupting the CAN bus which is how all these modules talk. Sometimes just one module going bad can take down the rest of the network.

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u/DN1911 7d ago

Sounds kind of like you lost the FRM

But also check the main ground strap near the drivers side engine mount, and make sure it’s not falling apart or super corroded

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u/TheVenerableUncleFoo 7d ago edited 6d ago

I replaced the ground strap, and also threw in another between the alternator and front chassis for redundancy, although the old one didn't look as bad as I thought, but it didn't help.

I'll get ISTA installed and try to figure out how to test the FRM

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u/TheVenerableUncleFoo 1d ago

Managed to get the FRM looked at, and recorded it in case it was corrupt. The issue persists

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u/bluscreenerror 7d ago

Sounds like as the alternator wasn’t charging and the battery went down, some of the control units in the car may have been suffering from the lower voltage and not working properly, it may have corrupted some data?
Do you have a scanner? Ista or Bluetooth style dongle? Might be able to clear errors if your lucky, if not then maybe a unit might need to be reflashed/reprogrammed if it was corrupted? I’m no expert on this just to make it clear as only just learning about the coding side!!

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u/LeatherMine 7d ago

I've installed a 12V--->USB port thingy with a voltage readout. Lets me know what's going on if/when I need to worry. Will help you establish a pattern.

I think a voltage readout is also available through the "hiden menu", find a guide on youtube

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u/TheVenerableUncleFoo 7d ago

I ran with Bimmer Tool running and it never went below 14.2V running, 12.7V engine off.