Toyota and Pedals Prompt Free Replacement

By: Bill Waters
03/24/2010 08:06 AM ET

Toyota and pedals have been the center of controversy since the January recall. Toyota has announced that they will replace the accelerator pedals if vehicle owners aren’t happy with the fixes.

“A replacement pedal should only be offered to a customer after the reinforcement bar has been installed and the customer has expressed dissatisfaction with the operation and/or feel of the pedal,” Toyota said in a memo to dealers.

Toyota Dealers have been inserting a piece of metal into the gas pedal mechanism since the January recall. This fix is to eliminate friction that was causing the pedal problem on more than 4 million vehicles. Toyota has said it is confident in its repairs and has found no evidence of other problems, such as faulty electronics.

The memo addresses Toyota vehicles that were listed in the January recall. More than 8 million automobiles were part of the recall notice. These vehicles include the 2005-10 Avalon, 2007-10 Camry, 2007-10 Tundra, 2009-10 Corolla, Matrix, RAV4; 2008-10 Sequoia and 2010 Highlander.

Accelerator Design And Engine Throttle

Automobile accelerators have historically been mechanical assemblies, which link the pedal to the engine throttle. This is usually done by linking a Bowden cable. With the advent of electronically controlled fuel systems, vehicle accelerators consist of a spring loaded pedal arm connected to an electronic transducer.

This transducer, typically a potentiometer or hall effect sensor, converts the position of the pedal arm to an electronic signal which is sent to an electronic control unit (ECU). The older mechanically designe not only provided a spring return, but the mechanism inherently provided some friction. This friction introduced mechanical hysteresis into the pedal force versus pedal position transfer function.

Put more simply, once the pedal was set at a specific position, the friction would help keep the pedal at this setting. This made it easier for the driver to maintain a pedal position. For example, if the driver’s foot is slightly jostled by a bump in the road, the accelerator pedal would remain at its setting.

Electronic Design

The Toyota electronic accelerator designs contain a special friction device. They are made of nylon 4/6 or polyphenylene sulfide within the pedal assembly to recreate the tactile response of older designs. According to the Toyota recall information, it is this device, which in some instances, has been preventing the accelerator pedal from returning to zero.

“The issue involves a friction device in the pedal designed to provide the proper ‘feel’ by adding resistance and making the pedal, steady and stable. This friction device includes a ‘shoe’ that rubs against an adjoining surface during normal pedal operation. Due to the materials used, wear and environmental conditions, these surfaces may, over time, begin to stick and release instead of operating smoothly. In some cases, friction could increase to a point that the pedal is slow to return to the idle position or, in rare cases, the pedal sticks, leaving the throttle partially open,” Toyota said in a statement.

Unintended Acceleration

The tactile response friction device in the affected Toyota electronic accelerator sometimes will create too much friction. This excess friction either slows the pedal return or completely stops it. In the worst case, once a pedal is pushed to a specific setting, it stays at the setting, even if the driver removes their foot from the pedal.

Early reports, in March 2007, involved the Toyota Tundra pickup truck, which used nylon 4/6 in the friction lever. Some questions and confusion exist if the Toyota explanation fully accounts for all instances of the unintended acceleration involving Toyota vehicles. CTS Corporation, the American manufacturer of the electronic accelerators that Toyota claims are at fault, issued the following statement.

“The problem of sudden unintended acceleration has been reported to have existed in some Lexus vehicles and Toyota vehicles going back to 1999, prior to CTS making this product for any customer. CTS believes that the rare slow return pedal phenomenon, which may occur in extreme environmental conditions, should absolutely not be linked with any sudden unintended acceleration incidents,” the company said in a statement.

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