Future route guidance application will make use of wireless traffic information exchange between vehicles and infrastructure roadside units (RSUs) to form a ubiquitous connected network known as the Internet of (connected) Vehicles (IoV). Current standards, such as Wireless Access for Vehicular Environment and ETSI Intelligent Transport Systems, for vehicular networking recommend elliptic-curve-based security algorithms to reliably share traffic information and provide defense against network attacks. However, data integrity attacks cannot be detected by the security algorithms proposed in the standards and can degrade the accuracy of an IoV route guidance application. RSUs have limited transmission range and rely on traffic information reported by vehicles within their range to estimate traffic density data in their vicinity. Malicious vehicles can transmit wrong traffic information, resulting in non-optimal route decisions. We propose a reputation algorithm known as RepGuide that enables reliable route guidance using IoV. RepGuide finds outliers in the traffic density information and identifies them as suspicious data. The algorithm then verifies the suspicious traffic information by multihop communication exchange with vehicles outside the transmission range of the RSU. Any suspicious data that cannot be verified is not used for finding optimal routes. Our performance evaluation results show that RepGuide reduces the travel time by 18 percent for an IoV route guidance application.