electrical problems after it rains
 

New owner of an '07 4.8i. Twice now I've experienced electrical malfunctions the day after the vehicle has been out in a heavy rain.

Symptoms:

• "transmission malfunction" message, warning that a gear could be selected without the brake engaged. Typically clears fairly quickly
• "electrical system malfunction" message, saying that further driving is not possible.
• CEL with various fault codes. Usually U0155 "lost communication with instrument panel cluster (ipc) control module", and sometimes P110F "Ambient Temperature Sensor Faulty CAN Signal"

Battery is only 1 year old, and load tests fine. Voltage is 12.35 with the ignition off, 14.35 with the ignition on, and around 13.7 while driving. I know 12.35 is a bit low, but the battery will accept and hold a charge no problem.

I suspect that the rain is getting into a control module and shorting out a bus. Forums say this is quite common with the E60 due to a blocked sunroof drain causing water under the spare tire to short out several control modules, but haven't found any similar issues with the E70.

Any suggestions where I should look?

i'd check all electrical compartments for (evidence of) water ingress to begin with.

Possibly water getting into the ATC CONTROL MODULE in the trunk. Bottom left corner next to battery. I had the identical symptoms and discovered a pool of water back there. That module is not water tight. Mine ultimately blew (couple months after the first error occurred) and I replaced it with one I sourced from a scrap yard.
I solved the water leak by removing, cleaning, and refitting the rubber boots that house the electrical wires running between the vehicle body and tailgate.

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Excellent information - thanks! I'll check this soon and let you know if that was the culprit. There's a lot of ECUs in the E70, and I'm not yet familiar with their locations.

I agree
I had my tailgate assist hatch module (right rearwell) get fried from water thanks to heavy rain on the interstate. After buying a used replacement it was plug and play and I silicones all the runner grommets and boots. All is well now!

Same here, but the water got in mine from a cracked sunroof cassette that was the result of a body shop removing it to access hail damage. I had all kinds of electrical warnings.

No water anywhere in the back, but it has been a few days since the rain. There are some minor signs of corrosion. I noticed that the right vent port on the battery is not plugged like it should be, so some corrosion might be due to hydrogen gas. Wire harness grommets look OK at first glance.

I'll soak it down tonight, and take some before and after pictures.

If it turns out not to be water in the back, are there any control modules under the hood that I should check? I recently replaced several plastic partitions in the engine compartment so that the long weather strip at the back of the engine would seal to the hood properly.

In the rear you check both side panels, by the wheel wells??

Yes. I removed both side panels, the tool kit access panel, and all plastic trays. I'm going to check the sunroof drains next, and do a water test.

There is some very light corrosion on the floor throughout, and I noticed some significant corrosion on an unused electrical connector near the floor on the right side beneath the fuse box. I recently replaced the 2nd stage brake light in the lift gate on that side due to water infiltration around the seal, but I don't think it's likely that water inside the lift gate could make its way back into the body.

Hopefully I'll get some time to do the water test this weekend, and I'll post pics and findings.

I am idly wondering if a short/issue at some bus connector somewhere can be triggering the odd collection of faults- so it might not be AT the specific module itself, but the fault at a distant connector causing spurious faults elsewhere? Just WAGing...

I strongly suspect a CAN bus module is failing somewhere. Sometimes my code scanner cannot connect via the OBD port.

Got around to wet testing today. All 4 sunroof drains were clear.

When testing the rear tail gate, water was getting around the left side wiring boot between the body and tail gate, at the body opening. The boots seemed to be in very good condition, but just don't seem to seal properly at the top of the opening in the body.

Water was entering the left rear, and soaking the fabric lining, especially at the bottom. Lots of modules were wet. A heavy rain would have flooded that compartment.

I put a bead of silicone around each opening to seal the boots to the body and tail gate, including an extra exterior bead at the top of the body seals. This silicone goes on white so it's easy to clean up excess, and dries clear.

Subsequent wet test passed. Hope no electronics were fried. I was able to pull up and clear fault codes, and so far they haven't returned.

Well, wont win any concours... but kudos for finsing the issue and posting!

Did you dry out all the modules and resolve all the other issues?? If so, excellent- lucky you got it before something fried

By the time I got around to checking things out, the modules had already dried out. It rained hard last night and the vehicle was outside. No leaks and no problems! So far so good.

New grommets aren't very expensive, but I suspect it would be a challenge to fish the wires through into the tailgate, so I'm not going to bother so long as the silicone holds.

yesterday, found water (again) in passenger side rear compartment. A month or more ago, tailgate module fried because of water there. At that time, I thought water got in there through side vents after pressure washing.

I was occasionally checking that area over coming weeks and things stayed dry. Yesterday, after a week of heavy rains (Seattle), checked again - water!

Luckily, I got to it while it was still raining and I observed water dripping from somewhere above. Traced it to the wiring boot.

Applied generous amount of silicone and reassembled.

It is a bad design, really. The opening for the wire on the body should have elevated edges. That alone would have prevented most water without any special seal. Instead, it is flat (see OP's pics) and we have to rely on rubber to stop the water. That doesn't quite work.

Also, observed little plastic flap of the sunroof drain (right next to the wiring boot) was pushed in too deep into the tube and not opening properly. Took it out, cleaned and pushed it in properly - now opens easily. That had a risk of flooding from sunroof.

Are those pics from the UPPER tailgate wiring? near the upper tailgate hinge?
or lower...

Upper

Same deal here a year ago. Fried my Tailgate lift module!
Ordered a used one on eBay and it came fried. Must be a common problem.
Round 3 I siliconed both boots like above where they enter the body and still get occasional water in right rear compartment.
Perhaps the boot is damaged and needs more silicone.
Great thread as I'm still hunting down the water intrusion!

I got into similar situation last weekend after 2 hours of heavy rain. Dont know what happened but I had a pool of water on the passenger side rear compartment with load of its underneath the battery tray. The fabric was wet from the compartment to the trunk floor arear.

I already soaked out the water but couldnt find the actual reason. Possibly sunroof but also the plasttric trim next to the taillight. Icould see it cracking and leaves a gap there but Im not sure. Any body has the part number for those 2 plastic pieces?i looked up on realoem but couldnt find

have you tested the drains on the sunroof? make sure they actually drain?


Seems better than replacing parts that might not be the issue...at least easier to test

I looked at my car again today and below are the pics.

The drain hole of the sunroof is sealed (?? or clogged) as in the picture.

Also there is a gap between the plastic shield and the taillight assembly on the body side.

Any insight as to how water enter the oddment tray next to the fuse boards and underneath the boot?

Thanks

Further test as suggested, I can safely confirm water drips through the roof drainage behind the D pillars onto the oddment tray and the interior fabric. Probably time to clean it up using the galvanized wire or air compressor gun

Careful with wire, you don't want to damage the tubing

Many have used plastic weed whacker line.

GL