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.

Sent from my SM-G930F using Tapatalk

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...