The B1904 Code is related with the car engine and it is necessary to fix the problem as soon as possible. The B1904 OBD2 may also be activated by problem of the earlier down the line. Suppose, a dirty MAF sensor might be producing the car to overreact in its fuel-trim changes. As a result, oxygen sensors are likely to report fuel mixture glitches. Body of the engine has the main problem of the car and it is necessary to fix the issue before running the car out. It is compulsory to fix all of the issues from the engine and when it is done, then take car out for test drive.