There are several reasons for the engagement of an accelerator pedal under a carpet. The carpet could be out of position, improperly installed, the wrong size, or improperly designed. Downloading the sensing diagnostic module, the modern vehicle's “black box,” can provide evidence of the malfunction. In one instance, a dealer had substituted another floor mat for the factory installed one, causing the malfunction. In another case, the insured supplied the floor mat. Clearly subrogation potential is dependent upon the claims analyst's investigation tying down the facts regarding the floor mat placement.

Figure 2B shows an accelerator pedal engaged in the polymer wear pad at a sewing seam. When the accelerator pedal was pressed, it readily engaged in the wear pad, which resulted in uncontrolled acceleration and an accident. This is obviously a design-related defect. Another cause of throttle malfunction is corrosion of throttle linkages. You will discern in Figures 3A and 3B (on the next page) a small ball joint that is part of a throttle assembly near the throttle plate. The ball joint eventually became difficult to articulate because of corrosion, causing the throttle to remain open after the accelerator pedal was released. This resulted in an accident, and in this particular case, corrosion-resistive plating of the metal parts was insufficient and was consequently found to be a manufacturing defect.

Shown in Figures 4A and 4B is a hand throttle linkage that was part of a manual throttle system used by disabled drivers. The linkage connected the accelerator pedal to a hand lever that would operate the throttle. While the driver was operating the vehicle, the throttle link failed, causing an accident. In Figure 4A, the arrow points to a fracture that occurred at a bend in the linkage. The photo to the right shows the fracture surface of the aluminum rod, which has evidence of metal fatigue.

Apparently, the installer of the system had bent the aluminum rod in order to facilitate installation, causing a crack that initiated a progressive failure scenario. The bend occurred at a hole provided for bolts used to attach the rod to the throttle system.  Metallurgical examination determined that metal fatigue had reduced the rod cross section to the point of failure. This is an installation-related defect with definite subrogation potential.

Electronic throttle control systems are being designed into more recent vehicles and may become a more prevalent throttle control system. Failure of electronic components may require analysis of an event data recorder (EDR) on the vehicle, which will often require that a manufacturer download the data, as the software is usually proprietary. However, the mechanical parts of the electronic throttle control system can exhibit failure modes similar to those shown in the case studies.

Figure 5 displays information collected from a crash data recorder download where a malfunction of the accelerator was suspected. From 5 seconds to 1 second before impact, the throttle percent was constant at approximately 72 percent (denoted by the solid blue line). The brakes had been applied (lavender line) and the vehicle was slowing from approximately 62 miles per hour (red line), at 5 seconds before impact, to 50 miles per hour at 1 second before impact. The engine was not at idle and varied from 3,200 to 3,600 revolutions per minute (green line). With the driver's foot on the brake, the percent throttle opening should decrease to near zero, as indicated by the dashed blue line. The data shows that the throttle stuck in a position of approximately 72 percent, which resulted in uncontrolled acceleration and an accident.

In cases where throttle control failure is claimed or suspected, it would be prudent for the claims analyst to inspect the vehicle to determine if evidence suggests a malfunction that could result in recovery from a party or even legal action. The evidence should be preserved for future inspection by various experts, including those of the manufacturer.