The B1901 Code describes about the problem of the engine and you need to fix the issues if you want to drive the car easily. The code is set for car engine and meaning of the code is not similar for all of the engine. Similar the all engines, the vehicle engine system services particularly advanced hydraulic lifters (known as switching roller followers) for the engine B1901 code intake and use valves. The lifters can be collapsed by disengaging an internal locking pin. The locking pin is detached using solenoids to modify oil compression fed into the lifter. You need to fix the problem with the professional.