27/07/2026 6:12 am
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Automotive Q&A
Cooling fan is commanded to 100% but its feed collapses under load
Review the evidence, add a focused answer, and distinguish confirmed measurements from assumptions.
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A 2015 Dodge Dart overheats only in traffic. Scan data commands the radiator fan to 100%, but the fan is stationary. With the connector unplugged, the power terminal shows 11.9 V. Connected and commanded, it falls to 3.2 V while ground drop remains below 0.1 V. The motor spins when supplied through a fused test circuit.
Where should the feed be divided next?
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28/07/2026 10:45 am
The unloaded voltage is misleading; the connected reading proves excessive resistance upstream. Move the positive meter lead from the fan feed back through the fuse, relay or solid-state controller and distribution junctions while keeping the motor commanded. Measure across each connection under the same load. Inspect fuse blades and bus contacts from both sides, not just the visible element.
If the fan current is within specification on the fused test supply, repair the segment with the largest voltage loss. Confirm both low- and high-speed strategies afterward.
Topic starter
29/07/2026 9:24 am
Most of the loss was across one maxi-fuse blade and its overheated terminal. The fuse element was intact, which is why the visual check passed. Replacing the terminal and fuse restored 12.6 V at the running fan, and coolant temperature stayed controlled during a 30-minute idle.