The situation when Nissan Almera stops cooling the engine, is one of the most critical for a car owner. If the radiator fan does not start even when the temperature reaches a high temperature, the risk of overheating of the power unit increases many times over. This can lead to deformation of the cylinder head, gasket burnout and costly repairs, so the problem cannot be ignored for a minute.
Many drivers notice the problem only when steam appears from under the hood or the temperature light on the dashboard comes on. However, diagnosing a malfunction requires an understanding of the operation of the cooling system as a whole. In modern models Nissan Almera (G15 and previous generations) the fan is controlled by an electronic unit that analyzes signals from sensors and turns on electric motor through the power circuit.
The reasons for failure can be as simple as a blown fuse, or more complex, requiring specialized testing equipment. In this article we will analyze in detail the fault finding algorithm, starting from simple checks and ending with electronic diagnostics. You will learn how to check it yourself fan relay and when to contact a service center.
Primary diagnostics: fuses and relays
The first step when detecting a non-working fan is to check the condition of the power supply circuit elements. In most cases, the problem lies in simple components that are easy to replace. Open the fuse box located in the engine compartment and find the corresponding element according to the diagram on the block cover.
If the fuse is intact, the next step is to check fan relay. This is a small device that closes the voltage supply circuit to the motor when it receives a signal from the control unit. Often the contacts inside the relay burn out or become stuck, rendering it inoperable. To check, you can try replacing the relay with a known good one, for example, the same one, but responsible for the operation of the sound signal.
- 🔍 Visually inspect the fuse for a break in the metal jumper inside the bulb.
- ⚡ Check for voltage at the fan connector when the ignition is turned on and the engine warms up.
- 🔧 Try to close the relay contacts with a screwdriver (observing safety measures) to check the functionality of the motor itself.
If after replacing the fuse and relay the fan still does not start, the problem may be deeper. Sometimes the culprit is the connection connector itself, which could have become oxidized due to moisture or overheating. Inspect the contacts for carbon deposits or discoloration of the metal, which indicates poor contact and high contact resistance.
Analysis of the operation of coolant temperature sensors
Engine management system Nissan Almera makes a decision to turn on the fan solely based on the readings of the coolant temperature sensor (CTS). If this sensor produces incorrect data, the electronic control unit (ECU) simply will not receive the command to start cooling. This is one of the most insidious malfunctions, since outwardly it shows no signs of failure.
The DTOZh can either completely fail or begin to “lie” in a certain temperature range. As a result, the ECU considers that the engine has warmed up to operating temperature, but has not reached the critical point, and the fan remains turned off. For accurate diagnostics, you need an OBD-II scanner, which will allow you to read real temperature readings from the sensor in real time.
⚠️ Attention: If the sensor shows a temperature of -40°C or +120°C with a cold engine, this is a clear sign of an open circuit or short circuit inside the element. In such cases, the fan will never turn on, since the control unit goes into emergency mode.
Sometimes the problem lies not in the sensor itself, but in the wiring to it. A broken wire, oxidation of the chip, or poor contact with ground can distort the signal. It is necessary to test the circuit from the sensor connector to the engine control unit, making sure there are no breaks or short circuits to the housing.
- 🌡️ Compare the scanner readings with the temperature dial readings on the dashboard.
- 🔌 Inspect the DTOZH connector for corrosion or moisture inside the contacts.
- 🛠️ Check the resistance of the sensor with a multimeter at different temperatures by checking the characteristics table.
- G15 (2012-2017)
- G15 restyling (2017-2020)
- G11 (until 2012)
- Other model
Checking the fan motor and power circuit
If the fuses, relays, and sensors are good, the next suspect is the fan motor itself. Over time, the commutator brushes wear out, the bearings wear out, and the windings can burn out. As a result, the motor stops rotating even if voltage is applied to it. This is a mechanical or electrical failure of the unit itself.
To check it is necessary to apply to the engine direct feeding from the battery. Disconnect the connector from the fan and use two wires to connect it directly to the battery terminals. If the fan starts working, then the problem was not in the motor, but in the control circuit or control unit. If the motor is silent or makes only a quiet hum, but does not turn, it needs to be replaced.
Sometimes the problem is wear on the motor shaft bearings. In this case, the fan may jam, which leads to a blown fuse or overheating of the windings. Before replacing a new unit, be sure to check whether the fan impeller rotates freely by hand. Any binding or play indicates that the entire assembly needs to be replaced.
- 🔋 Connect the motor directly to the battery to check its performance without intermediaries.
- 🌀 Check that there are no jams by rotating the impeller manually - it should move smoothly.
- 🔌 Inspect the power connector for melting of the plastic due to overheating of the contacts.
☑️ Checking the electric motor
The role of the fan control unit and resistor
On some modifications Nissan Almera the fan operates in two modes: first speed (low flow) and second speed (maximum flow). Switching between these modes is carried out through a power resistor or a special fan control unit. If the resistor is burned out, the fan may not turn on at the first speed, but work at the second, or vice versa - not work at all.
The power resistor is often located directly on or near the fan housing. It is subject to constant overheating, which over time leads to the destruction of the spirals or contacts. When diagnosing, it is important to check the integrity of this element, since its failure is a common cause of cooling system failure.
If your vehicle has a separate fan control unit, it may have its own internal fuses or transistors that fail. In such cases, replacing the entire control unit is the most effective solution to the problem, since repairing individual components inside the housing is often impractical.
⚠️ Attention: Never try to start a fan without an installed resistor or control unit, if this is provided by the design. This can lead to instantaneous burnout of the motor windings due to the lack of a current limiter.
In some cases, the problem lies in the wiring between the control unit and the power resistor. Oxidation of contacts in connectors or chafing of wire insulation can disrupt the control signal. A thorough inspection of the entire connection circuit will help identify hidden defects.
How to test a resistor with a multimeter?|To check a resistor, you need to measure its resistance between the terminals. If the multimeter shows infinity (open), the resistor is faulty and requires replacement. The resistance value should be within factory specifications, usually within a few ohms.-->
Problems with the engine control unit (ECU)
The most rare, but possible cause is a malfunction of the engine control unit (ECU) itself. Inside the ECU there are power relays or transistors that directly switch power to the fan. If these components fail, the unit stops issuing a command to turn on, even if all sensors show a critical temperature.
ECU diagnostics require sophisticated equipment and high qualifications. First you need to exclude all external causes
sensors, wiring, fuses and motor. Only after a thorough check of all other elements can the control unit be suspected. Sometimes the problem is solved by flashing the ECU, but more often the board needs to be replaced or repaired.
Sometimes the cause of failure is overheating of the ECU itself or moisture entering its housing. Moisture can cause corrosion of the tracks on the board or short circuit of the power switches. If the car was operated in high humidity conditions or after the engine was washed, it is worth paying special attention to the condition of the electronic unit.
- 💻 Use a professional scanner to check for errors in the engine management system.
- 🔍 Inspect the ECU housing for traces of moisture, corrosion or mechanical damage.
- 🔄 Check for software updates for the ECU that may correct fan control errors.
Comparison table of common faults
For clarity, we present a table that will help you quickly navigate the most likely causes of fan failure on Nissan Almera. Comparing symptoms and likely culprits will simplify the troubleshooting process and save time.
| Symptom | Probable Cause | Difficulty of repair | Probability |
|---|---|---|---|
| The fan doesn't turn on at all | Burnt fuse or relay | Low | High |
| First speed doesn't work | Faulty power resistor | Average | Average |
| Fan does not turn on when overheated | Faulty temperature sensor (DTOZH) | Low | High |
| The fan is jerky or noisy | Motor bearing wear | Average | Average |
| The fan does not turn on, but there is power | Jammed motor or broken windings | High | Average |
Please note that the high probability of problems with fuses and sensors does not negate the need to check all other components. A systematic approach allows you to avoid false conclusions and repeated visits to the service. The most critical mistake is to continue driving on an overheated engine, hoping that the fan will “turn on itself.”
If you are not confident in your abilities or do not have the necessary equipment for diagnostics, it is better to entrust the work to professionals. Incorrect actions can lead to worsening damage and increasing the cost of repairs. The safety and durability of your vehicle depend on timely and competent troubleshooting.
Regularly checking the condition of the cooling system and timely replacement of consumables (fuses, sensors) significantly reduce the risk of sudden fan failure while on the road.
Checklist for actions in case of engine overheating
If the temperature sensor lights up on the road and the fan does not turn on, it is important to act quickly and correctly. Stopping the engine and waiting for help is not always the best option if you need to get to a service station. However, precautions must be taken so as not to completely destroy the engine.
First, stop in a safe place and turn off the engine if the temperature gauge goes into the red zone. Open the hood for better cooling, but do not open the expansion tank until the engine has cooled down - the risk of scalding is very high. Check the antifreeze level and make sure there are no obvious leaks.
- 🛑 Stop the car and turn off the engine when the critical temperature is reached.
- ❄️ Open the hood and let the engine cool naturally before checking.
- 🔧 Try to manually check the operation of the fan by applying power directly, if you have the tools.
If the fan still does not start, but you need to get to the service center, you can try turning on the air conditioner. Sometimes the air conditioning system will force the fan to run at full power, which will help lower the engine temperature slightly. This is a temporary measure that will allow you to get to the nearest service station without overheating.
☑️ Actions in case of overheating
FAQ: Frequently asked questions
Why does the fan only turn on at second speed?
This indicates a faulty power resistor or first speed circuit. The electronic unit receives a signal about the need for cooling, but cannot activate the first mode due to an open circuit in the resistor. The fan runs at second speed because this circuit bypasses the resistor and connects directly.
Is it possible to drive a Nissan Almera without a fan?
Strongly not recommended. Driving a vehicle without a running fan is only possible in cool weather with low engine load. During traffic jams, climbs or hot weather, the engine will overheat in a few minutes, which will lead to serious damage.
How to check a temperature sensor without a scanner?
You can use a multimeter. Disconnect the sensor connector, turn on the ignition and measure the voltage between the signal wire and ground. As the engine warms up, the voltage should change smoothly. You can also measure the resistance of the sensor in hot and cold water by comparing it with a table of values.
The fan fuse has blown, is it possible to install a higher amperage fuse?
No, this is strictly prohibited. Installing a higher amperage fuse may result in a short circuit that will burn the wiring or the fan motor itself, not the fuse. Use only a fuse of the rating specified in the vehicle diagram.
Why doesn't the fan turn on when the engine is cold?
This is normal system behavior. The fan should only turn on when a certain coolant temperature is reached (usually around 95-105°C). If it turns on when the engine is cold, this may indicate a faulty sensor or ECU that incorrectly considers the engine to be overheated.