A faulty module regularly causes the cooling fan on the Seat Mii to keep running after you have switched off the engine. This often leads to a flat battery and can result in unnecessary repair costs. The cause usually lies in a fault in the fan control module, a defective sensor or poor contact in the wiring. In this article you can read how to recognise this problem and what to do about it.
Why does the fan on my Seat Mii keep running when the engine is off?
With the Seat Mii, a cooling fan that continues to run for a short while after switching off the engine is in itself normal. The fan helps to bring the engine and cooling system to the right temperature, especially after a hot drive or when the air conditioning has been on. This run-on behaviour usually lasts a few minutes and then stops by itself.
It becomes a problem when the fan keeps running for hours, even with a cold engine. In that case the fan continuously draws current from the battery. After a few hours, the battery will be flat and the car will no longer start. This problem often stems from a faulty module that controls the fan, a sensor that sends incorrect values or a fault in the wiring.
In modern cars such as the Seat Mii, an electronic system controls the fan. The engine management unit (the control system that manages the engine) receives information from the coolant temperature sensor and the air-con pressure sensor. Based on that data, the system determines whether the fan should run and at what speed. If one of these components is defective, the module receives incorrect instructions and drives the fan unnecessarily.
‘ This prevents overheating, but of course does not solve the underlying problem. ’
Possible causes of a continuously running cooling fan
There are several causes that can make the cooling fan on the Seat Mii keep running. Rule these out systematically. That way you avoid unnecessary replacements.
Defective temperature sensor
The coolant temperature sensor measures the temperature of the coolant and sends this information to the engine management unit. When this sensor fails, it passes on incorrect values. The car then thinks the engine is too hot and switches on the fan, even though the engine is actually cold.
Fault in the fan module or relay
The fan module (the part that controls the speed of the fan and determines when it switches on or off) controls the speed of the fan and switches it on or off. With a defective module, the fan remains stuck in a fail-safe mode. Sometimes a relay sticks, causing the power supply to the fan to remain on. This occurs more often in older cars or after exposure to moisture.
Problems with the air-con pressure sensor
In some models within the VAG group, including the Seat Mii, a defective air-con pressure sensor causes the fan to switch on unnecessarily. The car uses this value to protect the air-con system against excessive pressure. An incorrect reading leads to a fan that runs constantly.
Poor wiring or contact problems
Corrosion in connectors, a broken wire or contact resistance mean that the fan module receives incorrect signals. This type of fault is difficult to reproduce. The problem sometimes occurs and sometimes does not, depending on temperature and humidity.
Error codes in the engine management
When the engine management unit registers an error code related to the cooling system or the air conditioning, the fan continues to run as standard as a safety measure. This prevents overheating, but of course does not solve the underlying problem.
Symptoms that point to a problem
There are a number of recognisable signals that indicate the cooling fan on your Seat Mii is not functioning normally:
- The fan starts running immediately after starting a cold engine
- The fan continues to run at high speed after you have switched off the engine
- The battery regularly runs flat for no obvious reason
- You hear a continuous humming sound from under the bonnet, even when the car is switched off
- The air conditioning does not work properly or shows an error message
- A warning light for the engine or air conditioning appears on the dashboard
What should you check yourself before going to the garage?
Before going to a garage, check a few things yourself. This narrows down the cause. In addition, you avoid unnecessary diagnostic costs.
Check when the fan starts
Listen carefully to the moment when the fan starts running. Does it start immediately when you switch on the ignition, or only after the engine has been warm for a while? A fan that starts immediately with a cold engine usually points to a problem with a sensor or control module.
Inspect connectors and cables
Open the bonnet and visually inspect the connectors at the fan and the sensors (components that measure values such as temperature and pressure). Look for corrosion, loose connections, moisture or damaged wiring. Dirt or deposits on the fan module can also be an indication of a problem.
Check the coolant level
A coolant level that is too low can indirectly cause problems. Only check this when the engine is completely cold to avoid burns. The level must be between the minimum and maximum mark.
Have error codes read out
With a diagnostic device you can read whether any error codes have been stored in the engine management (the system that controls the engine) or the air-con system. Many modern garages and car dealers can do this for you. Pay particular attention to codes relating to the coolant temperature sensor, air-con pressure sensor, fan control or communication errors between the engine management unit and the fan module (the component that controls the fan).
Compare live data with reality
Do you have access to live data via a diagnostic device? Then compare the measured coolant temperature with the actual condition of the engine. Is the engine cold but the system indicates a high temperature? Then the sensor or the wiring to the sensor is probably defective.
How do you replace the fan module on the Seat Mii?
Does diagnosis show that the fan module is defective? Then you replace it. The module is usually located directly on or near the fan itself. Replacing it requires some technical knowledge and tools. With the right manual you can do this yourself.
The steps are as follows:
- Switch off the engine and disconnect the negative terminal of the battery to prevent a short circuit
- Remove any covers or parts that block access to the fan
- Disconnect the plug from the fan module
- Unscrew the fan module from the fan or mounting bracket
- Fit the new module and connect it according to the factory specifications
- Refit all parts and reconnect the battery
- Start the engine and check whether the fan operates normally
Are you unsure about your technical skills? Then have the replacement carried out by an authorised garage. Incorrect connection can lead to new faults or damage to electrical components.
Does regular maintenance prevent a defective cooling fan?
Regular maintenance prevents problems with the cooling fan. You will also detect issues at an early stage. A well-maintained cooling system works more efficiently and puts less strain on the fan.
Make sure you have the following checked every year:
- The coolant level and the quality of the coolant
- The condition of the hoses and clamps of the cooling system
- The operation of the thermostat
- The electrical connections of sensors and modules
- The condition of the radiator and fan
Visually inspect connectors and cables regularly. Do this especially after a period with a lot of moisture or salt on the road. Corrosion often develops gradually and can start before there are any visible symptoms.
Also keep the air-con system well maintained. A dirty condenser or an air-con system that has to work too hard can indirectly cause extra load on the fan and lead to earlier failures.
When should you see a specialist?
There are situations in which it is wise to go straight to a garage instead of trying to solve the problem yourself:
- The fan runs continuously at full speed, even with a cold engine
- Smoke, a burning smell or a melting smell is coming from under the bonnet
- The coolant temperature is really rising and the engine is in danger of overheating
- Error codes keep coming back after being cleared
- The air conditioning no longer works
- You have no access to diagnostic equipment to read error codes
An authorised Seat dealer or a garage with experience of VAG models has the right knowledge and equipment to diagnose the problem quickly and accurately. This prevents you from replacing parts that are not defective.
‘ On the Carnews website you will find much more information about common problems, maintenance tips and practical advice for this compact city car. ’
Discover more about the Seat Mii on Carnews
A cooling fan that keeps running is just one of the technical challenges that Seat Mii owners may face. On the Carnews website you will find much more information about common problems, maintenance tips and practical advice for this compact city car. Discover what other owners experience and how to keep your car in top condition.
Frequently asked questions
The most common causes are a defective coolant temperature sensor or air-con pressure sensor, causing the ECU to think that the engine or air-con system is too hot. Poor connector contacts or broken wires in the control circuit are also common, as are a faulty fan module or a relay that has stuck. In addition, an error code in the engine or air-con system can cause the fan to run almost continuously as a precaution. Pay attention to whether the behaviour changes when using the air conditioning and have error codes and live data read out to find the exact cause.
If the cooling fan runs constantly, this can place an excessive load on the battery, causing it to discharge more quickly or wear out prematurely, especially if the problem also occurs with the engine switched off. In addition, an underlying cooling or sensor problem that keeps activating the fan can mean that the engine is not cooled correctly (for example due to incorrect control), with a risk of overheating and engine damage.
You can first check whether the fan only runs on briefly after a drive with a hot engine or air conditioning, or whether it also starts (at high speed) immediately with a completely cold engine. Next, check the coolant level (only with a cold engine) and inspect the connectors and visible wiring around the fan, sensors and air-con system for corrosion, loose contacts and damage. Then use an OBD diagnostic tool to read error codes and look for codes relating to coolant temperature, air-con pressure sensor and fan control. Finally, compare the engine temperature shown in the live data with the actual cold/warm condition to track down a faulty sensor or wiring.
There are no broad, official recall actions known that specifically identify the cooling fan of the Seat Mii or technically related VAG models (VW up!, Škoda Citigo) as a series problem. In practice, however, similar complaints are regularly reported, such as a fan that keeps running (too) long unnecessarily due to defective temperature sensors, air-con pressure sensors, wiring or the fan control module. In these models, the problem is often found in the control system (sensors/connectors/module) rather than in the fan motor itself. Checking error codes, sensors and wiring is therefore the usual approach, rather than a standard replacement via a recall.
Often a defective coolant temperature sensor or a fault in the air-con pressure sensor is to blame. Problems with wiring or connectors (corrosion, broken wire, poor contact) are also very common. In addition, a defective fan module or a relay that is ‘sticking’ can prevent the cooling fan from switching off.