P0485

P0485 is a cooling-fan power or ground circuit malfunction — the ECM/BCM detected an electrical fault on the fan's primary power feed, ground return, or both. This differs from P0484 (rationality) in that P0485 specifies a measured circuit problem: open, short to power, short to ground, or excessive resistance. Cheapest-first ladder: pull the fan connector at the shroud, key-on engine-off, and measure voltage at the power-feed pin with a DMM (should be 12-14V battery voltage when commanded on, less than 0.5V when commanded off). Then ground-side: measure voltage drop from the fan ground pin to the battery negative post under load — anything above 0.3V indicates corrosion, a broken strap, or a chassis ground point with paint behind it. Then clamp-meter the current draw during a commanded fan-on cycle: 3-8A at low speed, 15-30A at high speed; less than 1A means an open circuit (broken wire, blown maxi-fuse, or open motor winding), more than 35A sustained means a binding bearing or shorted winding pulling the fan toward fuse-popping current. Inspect the fan blades and shroud for debris (mouse nests, leaves jammed between blade and shroud are surprisingly common). Expensive-misdiagnosis caveat: on platforms where the fan share a fused power feed with other cooling system loads (water pump on hybrid setups, AC condenser fan), a short in any one component pops the same fuse and sets P0485 — verify the fault is actually at the fan motor before replacing it, because pulling a transmission cooler line or a shorted AC wire can repeatedly destroy fan motors when current spikes route through them.

Vehicle-specific patterns: 1997-2014 Ford F-150 with the PWM electric fan throws P0485 when the heavy-gauge power feed from the under-hood relay/MaxiFuse box corrodes at the firewall pass-through or at the FCM connector — the high inrush current burns connector terminals over time. 2007-2014 GM 1500/2500 trucks (Silverado, Sierra, Tahoe, Yukon, Suburban) throws P0485 when the dual-fan power harness chafes against the radiator support and shorts to ground; GM issued TSBs on harness routing. 2008-2016 Dodge Grand Caravan / Chrysler Town & Country throws P0485 from the well-documented TIPM (Totally Integrated Power Module) fan relay failure — the internal relay solders crack and the relay either welds closed (fan runs constantly, kills battery) or fails open (overheat). 2011-2017 Jeep Grand Cherokee with the 3.6L Pentastar V6 throws P0485 from the same TIPM relay failures. 2010-2015 Toyota Prius (and other hybrid models) throws P0485 from inverter cooling fan failures that share fuses with the main radiator fan circuit. Estimated repair: $80 (corroded connector + dielectric grease) to $1,200 (TIPM replacement on a Caravan or Grand Cherokee).