The Worst Interface Ever

For $1500, you can equip your luxury car with a genuine self-destruct switch. Once it’s in place, you must remember to flip it whenever you shift from driving your car to not driving your car. Forget once or do it wrong, and your engine and transmission will self-destruct. “Ah, a fictitious switch,” you say, but no, it is all too real and all too destructive. The switch is hidden under the hood, where you cannot visually inspect it. To increase the sport, it's not only left unlabeled as to function, its two positions are unlabeled, too—make a mistake and, boom!, no more engine. Don’t bother looking in the manual that comes with it. The installers are instructed to place the switch any place and in any orientation that's easy for them to do their work. It sounds like the kind of dark nightmare that user interaction designers awaken from screaming, but it is a real, aftermarket device for Lexus RX-300 series cars being sold by a company in Florida.

As I reported back in July of 2002, Lexus has a small problem with their RX-300 series transmissions: They have a tendency to go bad if you tow the car any distance. This might not seem like much of a problem to you, but, then, you don’t live in a 40 foot motorhome, travelling the country. To people like us who must drag a car after us, towability is everything.

Lexus didn’t know they had a problem when they released the car, so they put a four year warranty on the transmission, specifically certifying it for towing. When the claims started coming in, they downshifted, and, in 2002, pulled all warranty coverage entirely for towing their new vehicles. That’s where these guys stepped in. They make well-reviewed aftermarket products to make untowable vehicles towable. In general, their products are well-engineered and built with solid, reliable components. Unfortunately, their design for the RX-300, while equally well-engineered, is a user-interaction disaster-in-waiting.

The pump runs fluid through the transmission while the car is being towed so the gears do not dry out—the problem Lexus had identified as causing the failures. A small fluid-shunt switch is used to switch between running the transmission fluid through its normal path or running it through the pump. Leave the switch in the wrong position, and you replace the possibility of a transmission failure with a sure thing:

  • If the car is towed without the switch in the pump position, no lubrication will take place while the car is being towed.
  • If the car is driven with the switch in the tow position, no lubrication will take place in the operating transmission.
    • The pump is not powered when the car is driven and, in a static state, blocks the flow of oil.

How do I know about this switch? I had one installed, at Lexus’s suggestion, but with my money, not knowing about the horrifying interface until it was too late and my $1500 was history. What did I do? What any combination human-computer interaction designer/licensed pilot would do: I went through the trouble of labelling the switch (not easy to do), then added it to our regular towing checklist. I would set the switch, I would check the switch, my wife would check the switch. Any normal user would not realize the importance of taking it on themselves to address the problem by labelling the switch and going through the checklists. Even those that went that far might not recognize the importance of having your copilot recheck your results. (That saved us once.) Because the switch is under the hood of the car, no casual glance will let you know you are facing disaster. Calling the company was of no help. The engineer who answered responded that nothing was wrong with the design of the switch that extremely careful operation would not overcome. He’d been using it for months with no problem. The problem could be easily corrected by the manufacturer replacing this manual switch with a solenoid-driven switch that only kicks in when the car has been connected for towing. This would add little to the already high price and would replace certain anxiety and uncertain calamity with a solid, dependable result.


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