In a letter dated April 9, 2012, a consumer petitioned the National Highway Traffic Safety Administration (NHTSA) to initiate a defect investigation of alleged stability control failures in model year (MY) 2005 Honda Pilot vehicles. The petitioner alleged that, "in the malfunctioning of these systems, steering failures occur and the brakes apply involuntarily." On June 4, 2012 the Office of Defects Investigation (ODI) opened Defect Petition DP12-002 to evaluate whether to grant or deny the petition. The petition is hereby granted.
The Vehicle Stability Assist (VSA) system in the MY 2005 Honda Pilot vehicles integrates braking control strategies for anti-lock braking, traction control, electronic stability control and brake assist functions. The system consists of a VSA modulator (an electronic control unit and electronic/hydraulic actuator) that receives data from an integral brake pressure sensor and from wheel speed sensors (four wheels), the steering wheel angle sensor and a combination yaw rate and lateral acceleration sensor.
Allegations of unexpected braking appear to be related to inappropriate activation of the brake assist (BA) function. The BA system is designed to minimize stopping distances in emergency braking maneuvers by rapidly applying maximum braking force when a panic stop is detected. ODI's analysis of complaints and information provided by Honda in its response to the DP12-002 information request letter have identified fault conditions that may result in false detection of a panic stop by the BA system, resulting in unexpected, severe brake application. ODI's analysis of consumer complaints has identified 185 incidents of unexpected braking of varying duration, including several allegations of rapid decelerations from highway speeds to near stops in highway travel lanes (VOQs 10450564, 10467571, 10427031, 10257672, 10453607). Honda implemented countermeasures in the control and fault detection algorithm in the MY 2006 Pilot VSA modulators, which are not interchangeable with the MY 2005 parts.
Allegations of steering anomalies appear to be related to inappropriate activation of the VSA stability assist function. The VSA system uses information from the wheel speed, steering wheel angle, yaw rate and lateral acceleration sensors to calculate the rate of change in vehicle side slip with respect to time. If excessive side slip is calculated, the system modulates brake force pulses to individual or combinations of wheels to maintain stability. Honda identified a problem with faulty yaw rate sensors sending an incorrect yaw rate signal to the VSA modulator. This may result in inappropriate VSA system activation, which is perceived by the driver as a momentary steering pull. The VSA control logic is designed to detect the yaw rate sensor faults in less than one second and place the system in failsafe mode, disabling all VSA functions. ODI has identified a total of 20 complaints that appear to be related to inappropriate VSA activation.
The petition is granted. Preliminary Evaluation PE12-028 has been opened to assess the scope, frequency, and safety-related consequences of the alleged defect.