The ABS/ESC control module continuously processes pulsed signals generated by the left-front wheel-speed sensor during vehicle operation. Sensor signal strategy depends on whether the vehicle employs passive variable-reluctance sensors or active Hall-effect / magnetoresistive sensors; code C0031 sets when the control module detects an open circuit, short to reference/ground, signal frequency dropout, or speed correlation implausibility relative to other wheel positions according to manufacturer-specific monitoring parameters.