Update: A portal to all of TTAC’s related articles on Toyota gas pedals is here:
Toyota has released their official “fix” for the sticky CTS-made gas pedals on the recalled models affected. From their graphic, it’s difficult to understand what parts are involved, and how they work. Thanks to our recent tear-down of the CTS pedal, we have the pictures and familiarity with the unit to explain it in detail.
The pedal is designed to have a certain amount of friction or hysteresis built in. This is done so that the fatigue of pressing the pedal continually is not onerous or becomes fatiguing. It also replicates the friction that would normally be present in a conventional throttle cable as it passes through its housing. A throttle assembly without the correct amount of friction or hysteresis would be very difficult to control smoothly.
Obviously, the exact amount of friction designed into the unit is very critical, so that the pedal returns as soon as the pressure is removed or reduced. The relationship of the spring pressure and built in friction must be stable and consistent. Toyota has stated that that is not always the case with the recalled CTS units, and that the degree of friction can increase over time due to wear and/or condensation, to the extent that the friction is greater than the pressure from the return spring. This would potentially cause a gas pedal to return slowly, unevenly, or not at all from the point where it was released.
This problem would not be the cause of “unintended acceleration” to the extent that the pedal would only stay open as much as it was before being released, although it could well be experienced as such. If the car was being accelerated briskly as on an on-ramp or hill, and the pedal stuck in that degree of openness, the car could well feel like it was accelerating on its own after the target speed was attained and the foot pressure reduced.
The affected part is in the lower center of the photo above (A), and in more detail in the one below. It is integral to the part that retains the return spring. The friction area is seen as the small “teeth” or “ears” protruding to the left at the very bottom of the picture. These two teeth ride in the two grooves of the pedal assembly (B), and are held against each other when the spring assembly is locked into position. The area of friction is seen as the grayish worn area on the teeth just beyond of the (crude) arrow.
From Toyota’s graphic (below) and from my experience handling the unit, it appears that there is a certain amount of free play of the spring retainer/friction block unit. In Toyota’s graphic below, it shows that unit tilting slightly, perhaps due to too much free play or wear of the plastic components. The steel reinforcement bar (red unit below) is apparently intended to stabilize the angle of the spring retainer/friction block unit, to ensure that the degree of friction is either more consistent or is compensated for the wear that has occurred.
We intend to secure a pedal unit and the steel reinforcement bar as soon as they are available for further examination and evaluation.