A steer-by wire steering system 501 for a vehicle is provided having a watchdog 516 to detect error states in at least a first actuator 502C, 502D and/or at least a first controller 510, with watchdog 516 inhibiting control of at least first actuator 502C, 502D if such an error state is detected. Most typically watchdog 516 is provided with a vehicle where first controller 510 controls first actuator 502C, 502D for a first group of wheels 504C, 504D, normally on a rear axle, and a second control means comprising two or more redundant controllers 508A, 508B, 508C controls a second actuator 502A, 502B for a second group of wheels 504A, 504B, normally on a front axle. In examples, a parameter used by second controller 508A, 508B, 508C may be adjusted if first controller 510 is inhibited. Watchdog 516 may also inhibit control of second controller 508A, 508B, 508C if an error is detected in the second controller or in second actuator 502A, 502B.
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