(Photograph by Justin Sullivan/Getty Images) The Prius, Toyota's technological flagship, may have a brake problem. Under certain conditions, according to the company, there may be slight interruption in the car's brake response. The fix, says Toyota, is a software update that dealers will download to all of the 133,000 2010 TOYOTA PRIUS
and 14,500 of the similar 2010 Lexus
HS250h models on the road.The brake system on these hybrids is complicated and different from what's on conventional cars. The system combines hydraulic brakes with brake regeneration and an anti-lock function. Under light braking, the calipers don't squeeze the rotors. Instead, the resistance of the electric motors provides the deceleration. This is how the TOYOTA PRIUS
captures the moving car's energy, charges the batteries, and later electrically boosts acceleration. Most hybrids work this way to keep fuel economy numbers high.Harder braking engages the calipers in a normal fashion. And finally threshold, or maximum braking engages the ABS system to keep the tires from skidding. The computer choreographs the various functions with inputs from several sources like the wheel-speed sensors, battery-charge meter, and brake-pedal stroke. Toyota
says that under certain conditions, like on an especially bumpy or slippery road, there may be brief momentary delay in the brakes response. The car will still stop—we're not talking about brake failure here--but the distance required could increase slightly. The software fix tweaks the software to better deal with those rare conditions. There are no new parts with this recall. The technician will simply hook a laptop to the car and download the new firmware. While there may be critics who decry the computer-controlled braking system, it should be noted that the TOYOTA PRIUS
wouldn't be so stingy with fuel without the electronic management. We've tested the TOYOTA PRIUS
several times and it easily tops 45 mpg in all types of driving.