What Causes the Passat's Cooling Fan to Keep Running When Cold?
4 Answers
Passat's cooling fan may keep running when cold due to a faulty thermal switch, damaged fan relay, or defective air conditioning pressure switch. Working principle of the cooling fan: The cooling fan typically provides a noticeable temperature reduction of 4-15 degrees Celsius. After the temperature drops, air is rapidly exchanged, significantly improving air quality. When the cooling fan is activated, negative pressure is generated inside the cavity, drawing external air through high-efficiency evaporative cooling pads to lower the temperature. This transforms into cool fresh air that blows out from the air conditioning vents, with outlet temperatures reaching 5-15 degrees Celsius while consuming only 1 kilowatt-hour of electricity per hour. Function of the cooling fan: An automobile engine operating in high-temperature conditions must be properly cooled to maintain optimal working temperature, ensuring good engine performance, durability, and meeting exhaust emission requirements. The cooling system plays a crucial role in this process, primarily consisting of components such as the cooling fan, radiator, and thermostat.
The other day I had an issue with my old Passat where the cooling fan kept running on a cold start. Took me a while to fix it. The main culprit is often a faulty temperature sensor—it's supposed to stop the fan during cold starts but falsely signals overheating, causing the fan to run nonstop. Another possibility is a stuck fan relay that remains in the 'on' position and won’t shut off. Here’s a quick checklist: First, check coolant levels—if low, it can trigger the fan to cool the system. Next, inspect the relay box location; feel for any unusual heat or burnt smells. Electrical shorts, like frayed wiring, can also cause similar issues by triggering false signals. A constantly running fan drains the battery hard, making cold starts difficult and risking battery or motor damage. Don’t wait—get it checked ASAP, ideally at a professional shop with diagnostic tools. My sensor replacement cost 800 RMB, but it prevented bigger losses. Fan issues may seem minor but impact safety—always monitor sensor health during routine maintenance.
My Passat had the same issue—the fan kept running when the car was cold. Later, I found out it was a problem with the temperature control system. Common causes include sensor failure or relay malfunction. The sensor misreads high temperatures and activates the fan, or the relay gets stuck and can't turn it off. First, check the coolant reservoir—low fluid levels can force the fan to run. Relays are usually located in the fuse box under the hood; inspect them for burn marks. Loose wiring connections can also cause issues, and a short circuit in the fan motor's wiring can trigger it as well. A constantly running fan not only drains the battery quickly but also makes cold starts difficult in the morning due to battery drain. During repairs, I recommend asking the technician to test the engine control unit—it might just need a part replacement. Ignoring this issue can lead to increased fan wear over time. After parking overnight, ensure the battery has enough charge.
When I drive my Passat, the cooling fan keeps running when the engine is cold. I looked it up online and found it's a common issue. It's mostly due to a faulty temperature sensor, which makes the fan run during cold starts when it should be off. Or the fan relay might be broken and stuck in the on position. Low coolant levels can also trigger the fan to start. Check these areas quickly to prevent the fan from draining the battery and affecting its lifespan. For safety, drive to a repair shop to scan for trouble codes—they can diagnose the problem faster.
