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I have never experienced as many water infiltration issues as I have in my BMW. Water flooded my DME (Main Engine Computer), which alarmingly killed the whole car. Then my Roof Function Center (FZD) became contaminated with road pollution, which absorbed moisture and caused serious problems with operation of the sunroof, the sound system, the SOS button, and the passenger airbag detection circuitry. Then my sunroof drains blocked, which saturated the interior of the car and completely flooded the trunk-wells holding the battery, the TCU, and the Top-HiFi Logic7 Amplifier.

When water infiltrates into electronics, it carries impurities, minerals, acids and ions that cause metals to corrode. If the electronics is powered up and working while water is present, electrical currents will take alternate paths, accelerate the corrosion, grow conductive mineral deposits, or worse still, cause metallic dendrite growth between the pins of electronic chips, which can result in a dead short. All of these have the potential to kill your electronics, sometimes long after the moisture has been removed.

IF the corrosion hasn't already resulted in catastrophic failures (by damaging or even burning components) it might be possible to save the board. It is important to consider the possibility that the board will not be recoverable, though, so you'll need a backup plan for module replacement. With that in mind, you have nothing to lose in trying to save your board. In fact, you could save yourself a great deal of money, especially if a new module would have to be coded to your car, as many of them do.

In all cases, it is essential to act quickly! As soon as possible, suck all of the water out of the compartment, disconnect the module, pull it out, open it up, remove the circuit board, and proceed with the steps below. My amplifier failure was detected fairly late, so I found corrosion all over the circuit boards, and it becomes more difficult to remove the longer it is left. Fortunately, I was still able to resurrect it.

Below, are the before and after pictures of a small portion of my Logic 7 Amplifier circuit board, showing the DSP chip (Digital Signal Processor) and its flash memory chip at the bottom left. Bad corrosion can be seen across all pins of the flash memory, and worse still, the possibility of similar corrosion underneath the DSP chip, which has 100 or so ball-grid-array pins beneath it.

Here's how to attempt repair if no burned parts are found:

• First, make sure you are grounded and not working with anything that might create static electricity (clothing, carpeting, plastic insulating mats, office chair, or whatever). Static KILLS electronics!
• If the infiltrating water was dirty or muddy, rinse the board in clean, warm water, then dunk the board in a tub of distilled water and agitate it side to side while holding the edges of the board.
• Do not dry the board yet. Instead, holding the board by its edges, shake the worst of the water off, then use "QD Electronics Cleaner" (or equivalent) with its nozzle straw to blast out any water and contaminants, especially underneath the chips.
• Submerse the board in a tub of 90% rubbing alcohol while scrubbing carefully around all of the chips and other components with a toothbrush. Use a new, soft-bristled toothbrush to scrub thoroughly in-between the pins, angling the bristles toward the chip and using tiny circles, just like brushing microscopic teeth. An old toothbrush will not get between the pins well enough. Take care not to use too much force or knock parts off the board!
• If stubborn, hardened deposits remain, use a needle to scratch lightly between pins. The goal is to remove any contaminants that might present a path for electricity to flow, or might encourage further mineral growth later, especially in wet or humid climates.
• Compressed air can help blast residues out from underneath chips, but again, take care not to blast any tiny parts off the board! Realize that compressed air may carry oil and water contaminants, so use filters to avoid that as much as possible.
• Soak, brush and agitate the board for a while longer in clean alcohol to get rid of any further residues or compressed air contaminants.
• Gently shake the board dry and place it for 24 hours over a warm air vent.
• Finally, spray the pins inside the mating connector (attached to the wiring harness) with contact cleaner and allow to dry. Make sure no water remains in the connector or harness.

My DME, FZD and Logic 7 Amp all came back to life and have worked perfectly, some of them for years, after doing this. It has cost me nothing but a few supplies and my time.

A few caveats to watch for...
Some circuit boards may have items on them that do not like to be soaked in alcohol. So, remove those items if possible, or work around them.
Example 1: The FZD board has silicone/rubber mats for all of the buttons. Those can easily be removed from the board and replaced after the board has dried.
Example 2: The Amplifier board has heat-generating power devices with thermal compound on them to maximize thermal contact with the heatsink. Preferably, wipe that stuff off with paper towels and once the board is clean and dry, use new thermal compound (typically used for CPU cooling in a PC). If insufficient compound is used when closing up the amp, the power devices could later overheat and fry.
Example 3: The Amplifier board has large capacitors that are coated in a soft glue that is designed to minimize vibration in the automotive environment. That glue reacts with the alcohol and the electronics cleaner, and creates a sticky, deteriorating mess. Just leave that glue alone. When the alcohol finally evaporates out of the glue, the glue will be okay, even if it shows cracks and white deposits. However, while cleaning, angle the board into the tub and try to minimize any alcohol/cleaner contact with the glue.