Cause
Seized or stiff fan bearings
A cooling fan whose bearings have stiffened or seized, so the motor cannot turn it at the commanded speed. It is a mechanical fault reported as an electrical one — the module sees current drawn without the speed to match and stores an underspeed or performance code naming the fan circuit.
Stiffness matters before seizure does. A bearing that has lost its grease drags rather than stopping, so the fan turns slowly, draws more current than it should, and runs hot — which cooks the motor and the speed control module in turn. So a stiff fan takes the control module with it, and replacing the module alone leaves the new one driving the same load.
Test it by hand with the vehicle off and isolated. A healthy fan spins several turns freely and coasts to a stop; a failing one stops almost immediately or feels notchy. Rocking the blade for shaft play finds the same fault earlier. Check the electric fan's current draw against specification if the tooling allows — a fan drawing well above its rating while reaching its speed is the warning that arrives before any code does.
Typically a moderate job.
Codes this can cause (4)
Codes where this is a likely explanation first, rather than merely a possible one.
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