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Poor Plastic Selection Caused Gas Pedal Failures

Poor Plastic Selection Caused Gas Pedal Failures

Toyota says a high-performance plastic used as friction levers in accelerator pedal assemblies causes the gas pedal to malfunction in certain weather conditions. Toyota outlined the problem in a recent letter to the National Highway Traffic Safety Administration, including details of problems dating to March, 2007, when internal testing on the plastic accelerated.

Chris Santucci, manager of technical & regulatory affairs for Toyota Motor North America, says:

"Due to the manner in which the friction lever interacts with the sliding surface of the accelerator pedal inside the pedal sensor assembly, the sliding surface of the lever may become smooth during vehicle operation. In this condition, if condensation occurs on the surface, as may occur from heater operation (without A/C) when the pedal assembly is cold, the friction when the accelerator pedal is operated may increase, which may result in the accelerator pedal becoming harder to depress, slower to return or in the worst case, mechanically stuck in a partially depressed position."

The problem was first reported in March, 2007 when Toyota received field technical information of accelerator pedals demonstrating symptoms such as rough operation or being slow to return to the idle position.

The accelerator pedal assemblies in the vehicles (Tundras) contained a friction lever made of the polyamide (nylon) 4/6 material. Toyota's investigation found that the material was susceptible to humidity, which could cause the friction lever to absorb moisture and swell. It is well known that nylon is a hygroscopic (water-absorbing) polymer.

In February 2008, the material of the friction arm was changed to PPS while investigations continued. "In June 2008, Toyota concluded that while accelerator pedal feeling could change under certain conditions, Toyota considered it to be a drivability issue unrelated to safety," said Toyota's Santucci in a Jan. 21 letter to Daniel C. Smith, associate administrator for enforcement at the National Highway Traffic Safety Administration.

Starting in December of 2008, Toyota received field technical information from Europe that the accelerator pedals using the PPS were also sticking. The reports predominantly involved right hand drive versions of the Toyota Aygo and Yaris vehicles. Toyota began a detailed investigation of returned pedals in March of last year.

"Internal inspection of the sliding surface of the friction lever and the pedal arm was found to be partially smooth," wrote Santucci. "Toyota conducted some duplication tests, and it was found that the internal friction could increase if moisture was attached to the sliding surface of the friction lever as the surface became smooth. This made the accelerator pedal stick in a partially depressed position under the condition where condensation occurs on the accelerator pedal."

When air conditioning was operating, the phenomenon did not occur.

As a result, Toyota lengthened the arm of the friction lever and changed its material to prevent smoothing on all vehicles produced in Europe, starting in mid-August of last year.

Starting last October, reports surfaced of problems in North America with pedals using the PPS material. The design solution is still being investigated.

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