EPS SYSTEM: Fail-safe

EPS system enters the fail-safe mode (that allows the steering force to be controlled without impairing the drive ability) if any of the input/output values to/from EPS system (power steering control unit) deviate from the standard range.
Power steering control unit controls the driving voltage to power steering solenoid valve for maintaining the power steering assist force when the fail-safe function is activated. (The engine speed signals control EPS system if any vehicle speed signal error is detected.)

Fig 1: EPS System Solenoid Valve Voltage Versus Vehicle Speed Graph (Fail-Safe)
Courtesy of NISSAN NORTH AMERICA, INC.

Error area and root cause	Cancel condition
Engine speed is 1, 500 rpm or more and there is no vehicle speed signal input for over 10 seconds during vehicle travel.	When a vehicle speed signal of 2 km/h (1.2 MPH) or more is inputted. Key switch is turned OFF to ON.
Vehicle speed signal has abruptly dropped from 30 km/h (19 MPH) or more to 2 km/h (1.2 MPH) or less within 1.4 seconds.