Error Code P1481 is set when the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) detects the radiator fan is not spinning as fast as commanded. The PCM regulates the speed of the fan, varying the voltage and ground to it. When the PCM sets the fan to spin at a certain RPM, and the fan spins lower than what the PCM commands, the code will be set.