Steering gear box function is one of the important requirements in heavy vehicles in order to reduce driver fatigue. Improper functioning of steering gear box not only increases the driver fatigue, also concerns the safety of the vehicle. In this present investigation, the engine oil mixing up with steering oil has been identified and steering gear box failure has been observed in the customer vehicle. The root cause of failure has been analyzed. Based on the investigations, in particular design of steering pump has been failed at customer end. The same design of steering pump were segregated and analyzed. Initial pressure mapping study has been conducted. The pressure mapping results revealed that the cavity pressure obstructs the flow of suction pressure. It indicates that obstacle at suction port due to the existence of internal leakage that causes back pressure in the internal cavity of steering pump which sucks engine oil. The primary mode of oil accumulation was because of cavity in the existing design. In addition, single lip seal and unsealed ball bearing was not suitable for particular functional requirement. In order to solve the issue, the cavity was closed by accommodating double lip seal and sealed ball bearing. After the proposed modifications, the pressure mapping study was conducted. The results indicated that the cavity pressure is not obstructing the suction pressure. So effect of cavity pressure was completely eliminated in the proposed design. The design changes have been implemented across all the vehicle models.