A motor vehicle controller that carries out a method which includes: receiving a signal indicative of a surface friction parameter, surface_friction, the surface friction parameter corresponding to a coefficient of friction between a road wheel and a driving surface; receiving a signal indicative of a position of an accelerator control with respect to an allowable range of positions, accel_ctrl_pos; determining a critical powertrain torque limit value PT_TQ_CRIT in dependence at least in part on the value of surface_friction; and providing a traction warning indication to a driver in dependence on the value of accel_ctrl_pos and PT_TQ_CRIT.