Why Your Radiator Fan Keeps Running When Car is Off ?
You’ve just parked your car, turned off the engine, and yet, you hear the radiator fan still running. This can be perplexing and might even cause a bit of anxiety about potential issues with your vehicle. Understanding why this happens, whether it’s normal, and what steps to take can save you from unnecessary worry and potential repairs. In this article, we’ll delve into the reasons behind this phenomenon, what it means for your car, and how to address it effectively.
How does the radiator fan work ?
The radiator fan plays an important role in your vehicle’s cooling system. Its primary function is to pull air through the radiator to help dissipate the heat generated by the engine. This is especially important when the car is moving slowly or idling, as there’s less natural airflow through the radiator.
Which Mercedes Model is Known for the Radiator Fan Running After the Car is Turned Off?
One well-known case of the radiator fan continuing to run even after the car is turned off is found in Mercedes-Benz models equipped with the M272 and M273 engines, commonly seen in:
E-Class (W211, W212)
ML-Class (W164)
CLK and CLS models
This issue is often linked to these underlying causes:
Common Reasons:
- Faulty Coolant Temperature Sensor
- The fan continues to run to cool the engine, misinterpreting the temperature as high, even when the engine is off.
- ECU or Relay Faults
- A defective fan relay can get stuck in the “on” position, or an ECU issue may miscommunicate with the cooling system.
- Malfunctioning Control Module (SAM or ECM)
- These control modules may fail to send the correct signals, leaving the fan active unnecessarily.
- After-Run Cooling Feature
- In some high-performance models (like AMG variants), the radiator fan may continue running for a short time after the engine is shut off to prevent heat soak, but excessive running indicates a problem.
- Battery Drain Concerns
- Continuous fan operation is notorious for draining the battery, which is why diagnosing and fixing the issue quickly is crucial.
Mercedes vehicles like the E-Class (W212) and S-Class (W221) are particularly known for customers reporting these issues. Addressing the root cause involves checking fault codes, inspecting the fan relay or temperature sensors, and ensuring there are no coolant leaks leading to faulty readings.
Case Study: Why is the fan still running when the car is off Mercedes?
Symptoms of a Radiator fan keeps running when car is off on Mercedes
When Radiator fan keeps running when car is off, it can be a sign of several potential issues. Understanding these symptoms can help diagnose the problem effectively.
Description of the Problem
#1 : Fan Running After Shutdown
- It’s unusual for the fan to continue running for a long period after the ignition is turned off (up to 6 minutes). This indicates a potential issue with the cooling system or the electrical components controlling the fan.
#2 : Fan in Degraded Mode When Ignition is On
- If the fan operates in a degraded mode when the ignition is on, it suggests that the system is not functioning optimally and may be compensating for a fault.
Possible Causes of the Radiator fan keeps running when car is off
Here are some possible reasons why the fan continues to run after the car is turned off:
#1 : Post-Operation of the Fan
- The fan may continue running after the ignition is turned off due to several factors, including the temperature of the exhaust gases, the transmission oil, and the engine coolant. This is sometimes a normal part of the cooling process to prevent overheating.
#2 : Air Conditioning System Pressure
- If the fan runs continuously, it might be due to an issue with the pressure sensor of the air conditioning system. If the refrigerant pressure is not correctly measured, the fan might be triggered to run indefinitely.
#3 : Diesel Particulate Filter (DPF) Regeneration
- In vehicles with a diesel particulate filter, the fan may run after the engine is turned off if the DPF regeneration process was interrupted. This process helps burn off soot from the filter, and if not completed, it can cause the fan to continue running to manage the excess heat.
#4 : Control System Malfunction
- The fan operation is controlled at multiple levels and can run at up to 50% of its maximum speed for up to 6 minutes after the engine is turned off to cool down the engine. If this operation exceeds the normal duration, it may indicate a problem.
#5 : Degraded Mode Operation
- If the fan starts running when terminal 15 is powered, it could be an intentional degraded mode of operation. This happens when the engine control unit (ECU) does not receive a signal from the water temperature sensor, causing the fan to run at maximum speed as a safety measure.
#6 : Signal Cable Issues
- If the PWM signal cable or LIN bus is defective, the fan might switch to degraded mode, causing it to run continuously.
Diagnosing the Problem
To diagnose why your car’s fan keeps running after shutdown, consider the following steps:
#1 : Check Temperature Sensors
- Inspect the temperature sensors for any damage or malfunction. These sensors control the fan operation based on the engine’s temperature.
#2 : Inspect Relays and Fuses
- Locate the relay in your vehicle’s fuse box. Swap it with a similar relay (like the one for the headlights) to see if the problem persists. If the fan stops running excessively, the relay might be the culprit.
#3 : Examine Wiring and Connections
- Look for any damaged or loose wiring that might be causing electrical issues. Faulty wiring can lead to continuous fan operation.
#4 : Test the Fan Control Module
- The fan control module can sometimes fail and cause the fan to operate incorrectly. Testing this module can help determine if it’s the source of the problem.
Solutions and Preventive Measures
Depending on the diagnosis, you might need to:
- Replace Faulty Sensors: If a temperature sensor is malfunctioning, replacing it can resolve the issue.
- Repair or Replace Relays and Fuses: Fixing or replacing stuck relays and blown fuses can stop the fan from running unnecessarily.
- Fix Wiring Issues: Repair any damaged wires and ensure all connections are secure.
- Service the Cooling System: Regular maintenance of the cooling system, including the fan, radiator, and associated components, can prevent such issues.
- Consult a Professional: If the issue persists, seeking help from a professional mechanic is advisable. They can perform a thorough diagnostic and ensure all components are working correctly.
How to remove the radiator fan ?
To remove the radiator fan, follow the following steps on watching the images below;
- Turn off the ignition and keep the transmitter key out of range of the transmitter (at least 2 meters away).
- Remove the engine cover (1).
- Remove the right engine compartment cover.
- Remove the engine air intake duct upstream of the air filter (2).
- Remove the engine air intake duct after the air filter.
- Disconnect the cable for the engine hood latch from the take-up well (3).
- Remove the cold air intake (3) from the brace (4).
- Detach the front bumper.
- Remove the brace (4).
- Detach the automatic transmission oil cooler from the fan unit (5) and set it aside with the lines still connected.
- Unclip the coolant hose from the fan unit (5).
- Unclip the switching valve with radiator mounting plate and set it aside with the lines still connected.
- Unclip the retaining clips (6) from the upper air guide segment (7) at the fan unit (5) and set aside.
- Disconnect the electrical connector (8) from the fan unit (5).
- Disconnect the electrical connector of the radiator flap servo motor at the fan unit (5).
- Remove the front and central parts of the lower engine compartment covers.
- Clip the lower air guide segment (11) onto the two unlocking tabs (10) at the fan unit (5), then fold it down at the hinge.
- Lower the vehicle.
- Unhook the fan unit (5) from the radiator supports and pull it out by lifting it upward, Ensure not to damage the hoses. Otherwise, it may cause leaks.
Where is the cooling fan sensor located ?
B11/4 Coolant Temperature Sensor
The cooling fan sensor, often referred to as the coolant temperature sensor (CTS) or engine coolant temperature (ECT) sensor, is typically located near the engine block or in the radiator. The exact location can vary depending on the make and model of the vehicle. Here are some common places to look:
- Near the Thermostat Housing
- In many vehicles, the coolant temperature sensor is located near the thermostat housing. The thermostat housing is often found where the upper radiator hose connects to the engine.
- Engine Block
- The sensor can be threaded directly into the engine block or cylinder head. Look for it in a place where it can measure the temperature of the coolant as it circulates through the engine.
- Radiator
- Some vehicles have the temperature sensor mounted on the radiator itself, usually towards the bottom, where it can monitor the temperature of the coolant as it exits the radiator.
How to Identify the Cooling Fan Sensor ?
- Wires and Connector: Look for a small electrical connector with two or three wires leading to it. This connector is attached to the sensor.
- Threaded Sensor: The sensor is usually threaded and screws into the engine or radiator.
- Proximity to Coolant Passages: Since the sensor needs to measure coolant temperature, it will be located near coolant passages or directly in the path of the coolant flow.
