The automobile meaning of the C1504 Code is available online and the meaning of the code is C for Chassis Code Problem is controller area network wiring bus and modules. 1 for MFG – Manufacturer Specific. 5 for Computer And Auxiliary Outputs. 0 for IC Circuit High Voltage and 4 for Cruise Vehicle Speed/Set Speed Difference Too High. Following this meaning of the code is not important thing but you can follow to learn only general information. The general meaning of the code is not important thing but general people may follow it for learning some information only. A test drive is suggested when the car engine is fixed.