What is the reason for the car's fan not running at high speed?
3 Answers
Car radiator fan cannot rotate at high speed due to the failure of the fan itself, which may be caused by a malfunction in the fan's temperature controller or relay. A thorough inspection of the radiator fan is required. If the fan can rotate at low speed, it indicates that the temperature sensor is not faulty. You can open the relay box and swap the positions of the high-speed relay and low-speed relay. If the fan starts running at high speed, it means the high-speed relay is faulty. Below is an introduction to the car's electric fan: 1. Definition: Operated by the engine coolant temperature switch controller, it generally has two-speed levels. The car's air conditioning system also controls the operation of the electric fan when turned on. The electric fan works when the engine needs cooling. 2. Function: It helps minimize the energy consumption of the car engine. The electric fan is usually installed behind the car radiator, although some car models have it installed in front of the radiator. The radiator temperature is regulated by the fan to ensure the proper functioning of the car engine.
Last time my car had the same issue, the fan was spinning extremely slowly. First, I checked the fuse corresponding to the fan in the fuse box, and sure enough, it was burnt black. Replacing it fixed the problem. If it's a relay issue, you'll hear a clicking sound but the fan won't move—you'll need to use a multimeter to check if the coil is conducting. Another time, I found the connector rusted from being soaked in coolant, and it took a while to clean it. Now during hot weather and long trips, I'm extra careful. If the fan doesn't spin at high speed, the engine can easily overheat, especially in traffic when the temperature gauge shoots up to the red line—it's really scary. The mechanic said that in older cars, worn carbon brushes in the fan motor can also cause insufficient speed, and the whole unit needs to be replaced.
Having repaired cars for over a decade, when the fan doesn't run at high speed, 90% of the time it's a wiring issue. Focus on checking three key areas: the 15A fuse labeled COOL FAN in the fuse box, whether the relay contacts are burnt, and the coolant temperature sensor connector. Last month, a Passat had issues because the connector wasn't properly reinstalled during coolant replacement, leading to fluid leakage that corroded the pins. The most troublesome case is when the electric fan resistor burns out—you have to remove the front bumper to replace it. Don't underestimate a non-functioning fan; the repair cost for engine overheating and cylinder scoring could buy five sets of fans. For a quick test, turn on the AC to force the fan to operate and check if the high-speed mode activates.
