The B0104 code indicates a problem with the blower motor control relay or its associated wiring. The vehicle’s Engine Control Module (ECM) is unable to properly control the blower motor because the relay is not functioning correctly or the wiring is damaged.
The relay that supplies power to the blower motor is burned out or has a poor contact, preventing the fan from receiving power.
Corrosion, frayed wires, or a damaged connector between the relay and the blower motor can interrupt power delivery.
If the fan motor is burned out or its internal contacts are damaged, it will not run even if the relay works.
Rarely, the Engine Control Module may have a software or hardware fault that misinterprets the relay status, but this is uncommon.
The definition is universal; the diagnostics are engine-specific. Open your vehicle for the codes documented for it:
Replacing the PCM is rarely necessary for B0104. The code almost always points to a relay, wiring, or fan issue. A PCM replacement should be considered only after all other components have been ruled out.
Yes, an OBD‑II scan tool is needed to read and clear the B0104 code. However, the code can often be diagnosed with a multimeter and a simple inspection of the relay and wiring.
The vehicle will run, but you may experience reduced heating or cooling due to a non‑functional blower fan. It is recommended to address the issue promptly to avoid discomfort and potential electrical problems.