Runaway in reverse

Apr 2, 2011 by

The insured’s Toyota Matrix exited a driveway and uncontrollably accelerated backward.  It then struck another vehicle.

GEI was assigned to inspect and photograph the vehicle to identify any conditions or defects in the throttle control and brake systems that could have caused or contributed to this accident.

This older vehicle, which was in very good condition before the accident, sustained collision damage to both the front and rear. Minor impact damage was observed on the right front fender.   More severe damage was observed on the rear hatch, lower rear structure, and left rear quarter panel.   The vehicle was drivable, despite contact between the rear structure and the left rear tire.

The National Highway Traffic Safety Administration had not issued any safety recalls or defect investigations related to the throttle control or brake systems for this make, model, and year vehicle.

The Matrix was equipped with an electronic throttle control system.   The accelerator pedal was connected to a position sensor, which sends electronic signals to the engine control module.  The engine control module then sends electronic signals to a throttle actuator on the throttle body in the engine compartment via the engine control computer.   This actuator moves the throttle plate, which controls engine speed. The accelerator pedal moved freely through its full range of motion and returned to the “off” position when released.   No damage was observed at the accelerator pedal pivot point, nor on the wiring, electrical connectors at the accelerator pedal position sensor, nor on the electronic throttle actuator.

The driver’s floor mat was a correct application for this vehicle, but was not properly secured to the retaining clip on the floor.   In addition, a smaller, unsecured aftermarket floor mat was observed on top of the factory mat.   A recently expanded safety recall (NHTSA 09V388000 and 10V023000), that addresses floor mat entrapment of accelerator pedals in a number of Toyota-manufactured vehicles, was not applicable to this vehicle.

Malfunctions in the electronic throttle control system trigger diagnostic trouble codes (DTCs) that are stored in the vehicle’s onboard diagnostic system.   A scan of this system revealed no stored DTCs.  Significant faults in the electronic throttle control system also cause the engine warning light to illuminate and often trigger a fail-safe “limp home” mode, in which throttle openings and engine power are restricted.

The engine started and ran normally with no fast idle or surging observed.   Cold engine idle speed was unremarkable at approximately 1,700 rpm.   The engine warning light properly extinguished after the engine was started.

The un-depressed initial brake pedal height was about four inches above the floor.  The first brake pedal application produced a 2.5-inch high pedal, which repeated for the next twenty applications, with no sagging or fading.  The pedal feel was firm.  When the engine was started, with the brakes applied, the pedal height dropped approximately 1 inch, which was normal.  The vehicle was not equipped with an anti-lock braking system (ABS).   The brake system warning lights operated properly.

The brake master cylinder fluid reservoir was at a serviceable level.   The brake vacuum booster hose was clean and dry.  No indications of fluid leaks were observed at the brake master cylinder, brake proportioning valve, front brake calipers, or rear brake wheel cylinders.

In order to verify that the brakes on this vehicle were more powerful than the engine, the brakes were applied and the transmission shifted into “Drive”.   The accelerator pedal was then pressed to the floor.   Although the engine speed increased to approximately 2,500 rpm, the vehicle remained stationary.   This demonstrated that the vehicle would not have accelerated had the driver been applying the brakes.

 
The vehicle was then taken for a short test-drive in the repair shop parking lot.   The brakes operated properly, and in a panic stop, locked all four wheels, stopping the vehicle from approximately 10 mph in both forward and reverse directions.

No unusual engine, transmission or brake system behaviors were detected during the test drive.

In summary, no DTCs were found in the system, the floormats were not a factor, the braking system operated properly, and the sudden acceleration experienced by the driver could not be duplicated during our test-drive of the vehicle.   Having eliminated electrical and mechanical vehicle component failures, the remaining possible cause of the accident was driver error.

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