Thinking Tech

Prius recall pales next to faulty software in Mercedes Sensotronic brakes

Prius recall pales next to faulty software in Mercedes Sensotronic brakes

Posting in Energy

Mercedes' Sensotronic brake problems five years ago blow the Prius hybrid's away, but the culprit was the same: faulty software.

Yesterday's recall of 133,000 2010 Toyota's Pruis hybrids isn't the first time ABS braking software has been a problem. In fact, Toyota's recall of 133,000 Prius hybrids and 14,500 Lexus hybrids is tiny compared to the mother of all electronic brake recalls.

Mercedes recalled almost two million SL500s and E-Class vehicles in 2004-05 and ended up scrapping its brake-by-wire Sensotronic Brake Control system for its major models. Hailed as the future in 2001, Sensotronic brakes were developed at a pricetag of $173 million by Bosch and then DaimlerChrysler AG.

The culprit? Faulty software.

"The technology eliminates the mechanical link between the driver's brake pedal and the brakes, substituting an electrical link that actuates the brake calipers. Customer complaints were linked to the failure of software for the brake system. When the system failed, the hydraulic system took over. But that resulted in a longer stopping distance and additional brake pedal effort by the driver," according to an Autoweek story in December, 2005.

Mercedes returned to conventional hydraulic brakes in its major models even though Mercedes insiders maintained the Sensotronic was better. Customers simply lost faith in the Sensotronic brakes. Mercedes is still scrubbing away the tarnish on its reputation.

Of course, Toyota isn't being hammered just for the relatively small Prius and Lexus hybrid recalls. Its problems all started with much, much larger sticking accelerator problem across most of its major models.

Larry Dignan in a post this morning asks how software updates and bug fixes can be downloaded to automobile systems. Indeed, today's models after the driver are essentially controlled by computers. Arguing that computers and software should be excluded from cars is silly. After all, jetliners could not fly without myriad computers. We can't turn back the clock or technology.

But for years now, we've seen the results of bad software in automobiles and there's just going to be more of it as cars transition to electric powertrains. The Prius software problem could be just the tip of the iceberg.

Sensors, controllers, actuators and software comprise brake by wire systems. credit: Wikipedia

As for updates and patches, your car could download them over a wireless link just like a laptop. Or, you could download patches from the Internet onto a memory stick embedded in your car key or fob. Start the car, and the patch is downloaded.

Perhaps, this is something manufacturers should have thought about when cars became so dependent on software. No fuss. No bother. Anything to keep me away from the dealer.

One other downside to rising automotive complexity: do-it-yourselfers have been removed from car repair and maintenance for all but oil changes and swapping out like air filters. There's no more tinkering with a mechanical carburetor or bleeding the brakes yourself. Cars are too complex for that.

Advances in technology, environmental requirements and safety and performance improvements drive automotive engineering. But I also see complexity as a conspiracy to drive you back the dealer when anything goes wrong. Technology marches on.

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John Dodge

Contributing Editor

Contributing Editor John Dodge has written for the Wall Street Journal, Boston Globe, PC Week (now eWeek), EDN, Design News, Electronic Business, Bio-IT World, Health-IT World, Lowell Sun, Haverhill Gazette and Newburyport Daily News. He is based in Massachusetts. Follow him on Twitter. Disclosure