The right and left high-pressure oil rails are connected by an HPOP crossover line. This enables the PCM to monitor both high-pressure oil rails pressure. For a smoother engine operation, the HPOP crossover line removes ICP spikes. It will also help to feed oil to injectors better. The HPOP crossover line also balances oil pressures to make the engine operation quieter. However, it is another source of leaks.