NHTSA reviewing third generation Toyota Prius braking

By Mark Kleis - Posted December 24th 2009

At least dozens of owners of the latest, third generation Toyota Prius have filed complaints with the National Highway Traffic Safety Administration in regards to alleged brake failures they’ve experienced. The complaints are centered around the transition from regenerative to traditional braking, and the possibility that extra force is required to properly slow the vehicle.

According to analysis by The Detroit Bureau, the issues seem to be entered around issues with the regenerative braking system, which is a core component of Toyota’s hybrid technology. The regenerative braking function allows the vehicles to recapture energy while braking, allowing the hybrid to run on electric mode rather than from the gasoline engine.

In the case of several of the complaints, the Prius either has diminished braking power, or possibly even surges forward with unintended acceleration depending on which complaint you review.

“What I, and others have been experiencing, is certainly not “runaway acceleration” or anything to do with pressing the gas pedal,” Robert Becker, 2010 Prius owner told The Detroit Bureau.

“But rather the loss of braking power or braking momentum when hitting a pothole, manhole cover, or the like. This requires the driver to press down again harder on the brakes to slow or stop the car,” Becker said.

Another Prius owner who filed a complaint offered a more thorough explanation for their experience, “There have been several incidents in which my car seemed to surge forward while I was in the process of braking and hit a bump, railroad tracks or pothole. Initially, I convinced myself I must have been letting up on the brake when I hit the bump, but when this same thing happened three days ago on slippery, icy roads, I knew for 100% certain I had not let up on the brake. My car surged as I was slowly pulling up to a stop sign and gently braking. I came very close to hitting the car in front of me, had to push down on the brakes very hard, which activated the abs.”

The alleged problems with the Prius’ braking system go beyond simply being a possible danger to its occupants, but some are raising concern of the hazard posed to pedestrians and other motorists. Given the frequency of lacking deceleration while approaching stop lights, stop signs and on surface streets, pedestrians are at a particularly high level of risk.

An internal NHTSA memo echoed the concerns for pedestrian safety, “It appears that when you hit a bump, the regenerative braking (front wheels only) cuts out, and there is a short delay until the friction braking kicks in. This results in loss of braking, which is experienced acceleration (due to sudden end of deceleration from braking). Net impact is still a loss of braking/ increase in stopping distance. This could be fatal for pedestrians — it happens when approaching stop lights if you hit a pothole.”

When Toyota was approached by The Detroit Bureau about this matter they initially said they were unaware of the issue, but later released this statement, “We are aware of the complaints filed with NHTSA. The agency has not opened an investigation. We are investigating the issue based on internet traffic, customer comments to Toyota Customer Relations, and NHTSA complaints. It is too early to speculate the final conclusion(s) of our investigation and subsequent actions.”