The car has a sunroof, and the sunroof has two gutters and tubes that route rainwater through the body of the car and dump it outside. But like all gutters, they can get plugged with debris — and when that happens, water leaks through the sunroof and onto the floor of the car. Which happens to be where the engine control unit (ECU — the car's brain ) lives, right under the front passenger's feet. And ECUs, as you might suspect, don't do well in water.

I first realized there was a problem when everything in my car quit working. The car started stalling and spitting out error messages about every system it had — airbags, stability control, etc., etc. A helpful mechanic pulled the ECU board out and showed it to me — yup, basic Motorola* microprocessor plus all the fixin's, all fried. Volkswagen wants $1,200 for a replacement board. Ouch.

Now, why would you design a car with a key electronic component — an expensive, mission-critical, water-intolerant component — located at the lowest point, in a spot where it's likely to get wet? After all, aside from gutter malfunctions, people sometimes spill their grande lattes, or they shampoo the carpets, or they hop in with wet boots or wet dogs or whatever.

Maybe, I thought, there was some thorny design constraint and they had no other choice. But then my helpful mechanic told me, "Yeah, when this happens with Passats, we just put the new ECU board on the side of the footwell — there's plenty of room there, and it stays dry." It is difficult to keep from writing ungentlemanly words here.

To me, this is a prime example of the perils of failing to think about the whole system. I suspect that the ECU in my Passat is a really nice design — great hardware, robust software. But when it gets wet, none of that matters.

As systems get more complex and interdependent, it's crucial to maintain a whole-system perspective. Don't fry your Fahrvergnügen.

*now Freescale

Jeff Bier is the president of Berkeley Design Technology Inc. (www.BDTI.com), a benchmarking and consulting firm focusing on digital signal processing technology. Jennifer Eyre White of BDTI contributed to this column.