A vehicle occupant protection apparatus includes an occupant protection device, a control unit, and a sensor module. The sensor module includes an acceleration sensor for detecting first acceleration caused by a collision and second acceleration caused by a fault diagnosis of the sensor module, a signal processing circuit for producing first and second data corresponding to the first and second acceleration, respectively, and a signal output circuit for outputting a signal having the first data or the second data to the control unit. The control unit includes a diagnostic unit for performing the fault diagnosis based on the second data and a controller for controlling the protection device based on the first data. The signal output circuit adds a first code to the signal having the first data and adds a second code to the signal having the second data.