The diagnosis B1504 Code is related with the car engine and without resolving this problem, you should take the car for drive. The code identification of the problem of engine what is related with the body of engine. That is why, the component of the engine is not necessary to change. You can fix the problem if you have expensive machineries and tools. The dictionary meaning also defines the code too and that is B for Body Code Problem is antilock brake system, electronic suspension and steering systems. 1 for MFG – Manufacturer Specific 5 for Computer and Auxiliary Outputs 0 for IC Circuit High Voltage. 4 for Cruise Vehicle Speed/Set Speed Difference Too High.