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.
Poor Plastic Selection Caused Gas Pedal Failures
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