What must be checked if a fan motor is not receiving power despite functioning when connected directly to a battery?

When a fan motor operates properly when connected directly to a battery but fails to receive power during normal operation, it indicates that the issue lies within the circuit that leads to the fan motor. Checking the relay operation is crucial because the relay acts as a control switch for the fan motor. If the relay is malfunctioning or not engaging, it will not allow power to flow to the fan motor despite the motor being functional.

The relay typically receives a signal from the vehicle's control system when the fan needs to be activated. If there is an issue with the relay—such as a faulty coil, a stuck contact, or a missing signal—it will prevent the fan from receiving power, thereby leading to the symptoms described. Verifying that the relay functions correctly ensures that it can successfully complete the circuit to power the fan motor when required.

Other checks, such as verifying battery voltage, examining fuses, and inspecting wiring continuity, are also important diagnostic steps. However, given that the motor functions when directly connected to the battery, the immediate issue likely stems from the relay, making it the most critical component to investigate first in this scenario.