Vibration characteristics of a machine change with the operating conditions (speed, load, fault and etc.). Gears are widely used as power transmission device due to its flexibility to operate at wide range of speed and load. Any faults in the gear can lead to complete failure or even seizure of machine. Therefore, predictive maintenance strategy is adopted where the monitoring of condition of gear is done by analyzing the signal (vibration, acoustics, current and etc.) of gear. Modelling of a physical system is economical due to the cost involves in experiments. Moreover, the models are scalable and several types of faults can be introduced into it. In the present study, a gear kinematics based 9-degrees of freedom (DOFs) model is considered to find the response of the gear in healthy as well as in faulty (broken or may be missing tooth) conditions. A higher contact ratio spur gear system is considered for analysis. The model consists of a gear-pinion pair, a loader and a driver. The equations of motion of planer block diagram model of gear-pinion system are solved in Matlab-Simulink environment to study the response of the healthy and faulty gear. This study can be extended for different gear systems to find out the fault symptoms under missing/broken tooth.