P0484

P0484 is a cooling-fan rationality fault — the ECM/BCM commanded the fan to a specific speed or state and the feedback signal (PWM duty cycle, current draw, or speed sensor input on smart fans) did not match the commanded value within the manufacturer's allowed window. This is different from P0480/P0481/P0482 (specific relay or speed-control circuit faults); P0484 is the "you asked for X, you got Y" code. On modern PWM fans, normal commanded duty cycle sweeps from 0% (off) to 100% (max) and the current draw sits at 3-8A at low speed, 15-30A at full duty, with brief inrush spikes of 40-60A on startup. Cheapest-first ladder: scan-tool live data for commanded fan duty vs actual fan speed (or actual current draw on amperage-feedback systems). At idle with AC off, expect 0-20% commanded; with AC on or coolant past ~210F, expect 30-60%; at high load or coolant past ~225F, expect 70-100%. If commanded jumps but actual stays flat, the fan or driver is the suspect. Backprobe the fan power feed with a clamp meter during a duty-cycle sweep — current should track duty linearly within +/- 10%. Then check the fan ground (drop test, less than 0.2V under load) and the PWM signal at the fan connector with a scope (clean square wave, no chattering edges). Expensive-misdiagnosis caveat: a $40 cracked solder joint inside the fan-control module (FCM) or a single bad ground strap will exactly mimic a $300-$700 failed fan motor — always verify the control side before replacing the fan assembly.

Vehicle-specific patterns: 1997-2014 Ford F-150 (4.6L, 5.4L, 6.2L, 3.5L EcoBoost) uses a PWM electric fan with a dedicated Fan Control Module bolted to the shroud and is the most common P0484 case in domestic shops — the FCM cracks internally from heat cycles and either commands the fan to max constantly or fails to respond at all. 2007-2014 GM 1500/2500 trucks (Silverado, Sierra, Tahoe, Yukon) use BCM-controlled dual electric fans and frequently throw P0484 when the BCM's fan driver MOSFETs degrade — the symptom is fan running constantly with AC off, or never spinning up under load. 2008-2020 Dodge Grand Caravan / Chrysler Town & Country with the 3.3L / 3.8L / 3.6L V6 uses a hybrid setup (mechanical clutch fan plus auxiliary electric) and throws P0484 when the auxiliary fan relay corrodes in the underhood TIPM (Totally Integrated Power Module) — Chrysler issued multiple TSBs on TIPM failures. 2010-2016 BMW with the N20/N55 platform (328i, X3, X5 35i) throws P0484 when the electric fan module fails internally; common in 80k-120k mile range. Estimated repair: $120 (relay or ground strap) to $900 (full fan assembly + module on a BMW N55).