NHTSA Engineering Analysis EA09006

On April 28, 2010, Toyota Motor North America submitted a Defect Information Report (NHTSA Recall No. 10V-176) to NHTSA describing a problem in the Vehicle Stability Control (VSC) system in approximately 50,000 Model Year (MY) 2003 Toyota Sequoia vehicles.According to the report the centering position of the Steering Angle Sensor (SAS) in the MY 2003 vehicles may not be stored correctly due to a logic problem with the Skid Control Computer programming.The VSC system uses the information from the SAS to calculate the driver's intended vehicle direction.This information is cross referenced to sensors that tell the system which direction the vehicle is actually going and the system will, if it determines a variance indicating the vehicle is in a over-steer or under-steer condition, reduce throttle control and apply braking to make a correction in vehicle direction towards what the system believes is the driver's intended path.Toyota dealers will replace the Skid Control Electronic Control Unit in recalled vehicles.Toyota has indicated to NHTSA that it does not believe that inappropriate activations of the VSC system present an unreasonable risk to safety because it believes the activations are rare and tend to occur at low speeds when the vehicle is fully controllable and that the activations do not last more than a few seconds.Based on interviews with complainants ODI believes that the majority of the inappropriate activations of the VSC system occur when turning at low speeds, such as when a driver is pulling into or across the flow of oncoming traffic.Complainants report the effect produced by the malfunction of the VSC system is to leave the vehicle without the ability to accelerate up to speed, essentially leaving them creeping along exposed to oncoming traffic, because of the brake activation and reduction of throttle control caused by the VSC system.Complainants report that the events can last up to 10 seconds and some complaints report that oncoming traffic had