The valves of each cylinder are kept closed using a pair of arms that replace the conventional engine’s roller-type rocker arm. The engine P1821 code is one of these arms what follows the cam profile while the second arm connects to the valves. During normal engine operation the two arms are joined by a locking pin. You need to fix the car engine properly and it is easy to solve the car engine problem if you have experience and you have all machines, you can solve the car engine problem easily. The real meaning of the code is very important thing.