Error Code: E1 (Pump P1, Propo-Valve)

Hi all Recently i have encountered the above error code on my SK135SR. After this error has appeared, the left track & bucket movement are very slow, even at high flow. I have tried to swap the solenoid valves between P1 & P2 (Main Pump Area), I even changed the P1 valve (DRDE5K-31/30C50) to a new piece, yet the problem persist. What and where does the problem lies? Anyone to share their experience? Thanks in advance.