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Checking the electric fan with ECU at Peugeot & Citroen (PSA) without connecting to the car.

In order to check the electric fan with an ECU without a car, you need:

  1. First you need to measure the resistance between Signal and + Ubat (K.30). It should be between 1.5 kOhm and 2.5 kOhm. If the resistance is less than 1.5 kOhm or more than 2.5 kOhm, then this indicates that the fan is defective, or its life is coming to an end, despite the fact that it can still work for some time. When measuring the resistance between Signal and + Ubat (K.30), nothing must be connected to the fan except a measuring device!
  2. Next, you need to apply a 12 V supply voltage from the battery or power supply to the +Ubat(K. 30) and GND (K. 31) contacts of the power connector, designed for a maximum current of at least 30 … 50 A (depending on the type of fan).
  3. If there is a relay on the harness, then to turn it on, connect the + Relay input to + Ubat (K.30). And for a 4-pin connector, connect the -Relay input to GND (K.31).
  4. For CITROEN C3, you also need to drop +12 V to the Ignition input.
  5. If +12 V is applied to the Signal input or nothing is connected (left in the air), then the fan should gradually spin up to maximum speed.
  6. If mass (GND) is applied to the Signal input, the fan should stop completely.
  7. To smoothly change the speed, a pulse PWM signal with a frequency of 100 Hz must be applied to the Signal input.
  8. In order to check the Diagnostics output, connect a 10 kOhm resistor between + Ubat (K.30) and Diagnostics, and also connect a voltmeter between GND (K.31) and Diagnostics.Then apply 12 V to the contacts of the power connector + Ubat (K.30) and GND (K.31) from a source designed for a current of 30 … 50 A. Connect Signal input to +12 V or nothing. After the fan starts to spin up, measure the voltage between GND (K.31) and Diagnostics, it can gradually increase from 0 V to 1 V at the maximum fan speed. If the measured voltage exceeds 1 V at the maximum speed of rotation this will cause an error related to the fan malfunction recorded in the engine ECU. This error may cause the fan to work incorrectly or not start at all. But with this error, the fan can be started forcibly (as described above) or using the diagnostic program on the car itself.
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Since 1996, BMW began to install a controlled thermostat with an opening temperature of 105c on gasoline cars (as an example: thermostat 11537586885 for engine BMW n62, n63, n73, n74, s55, s63; thermostat 11537509227 for engine BMW m52, m54, m56; thermostat 11531436386 for engine BMW m62). Since then, the so-called BMW thermostat problem has been haunting these cars, because of the high operating temperatures, the wear and rapid failure of all engine units have sharply increased, as well as of the automatic transmission and exhaust system catalyst. For this reason, performance cold thermostats 11537586885, 11537509227, 11531436386 for BMW with an opening temperature of 90C appeared.

There is a strictly defined operating temperature for the engine that provides optimal working conditions. As a rule, within 90C. At lower temperatures, the engine oil does not have sufficient fluidity, which means that its resistance increases when the pistons move. At higher temperatures
– engine overheating (as an example, the above-mentioned BMW engines. One of the most common is n62, where the thermostat 11537586885 was originally installed with an opening temperature of 105c, not 90c).

The cooling system is designed to maintain an optimal operating temperature: when starting the car, you need a quick warm-up, and then, in the process of driving, you need high-quality cooling.   The thermostat takes over the regulation of this process, which is installed at the “fork” between the large and small circle of the cooling system and controls the direction of the coolant flow.

Until the engine is warmed up, the thermostat closes the pipe to the radiator, directing the coolant to a small circle: from the motor jacket, through the thermostat, bypass channel and back to the engine. Antifreeze does not pass through the radiator and does not cool, allowing the motor to warm up faster.

When the engine warms up to operating temperature (usually 90s), the thermostat opens the valve leading to the radiator, and the antifreeze begins to cool itself and cool the engine. Depending on the temperature of the antifreeze, the thermostat can close the valve to the bypass channel completely (when the engine needs intensive cooling) or partially.

Thus, the thermostat in a completely autonomous mode regulates the amount of antifreeze entering the cooling radiator, to keep the engine temperature at a constant operating level. On modern cars, thermostats can be equipped with an additional temperature sensor and heater (such as BMW thermostats 11537586885, 11537509227, 11531436386), paired with an electronic control unit. At medium engine speeds, the coolant temperature is maintained at a higher level, and at maximum load, additional heating is turned on, and the thermostat is triggered earlier, which allows you to reduce the temperature of the antifreeze by about 10°C. This decision can be controversial, since over time, the additional heater may fail.

Thermostat malfunctions: signs, causes, consequences.

Scale on the stem, corrosion on metal parts. As a rule, deposits in the cooling system appear due to poor-quality antifreeze and untimely replacement. Scale on the thermostat parts makes it difficult for the stem and valves to move, after that, the thermostat stops responding correctly to changes in the coolant temperature.

Failure due to vibration. More often, this problem happens with defective or low-quality products, in which the joints and connections are not sealed enough. If the copper cylinder is not sufficiently sealed, coolant will enter and prevent the thermostat from operating.

Destruction of the rubber seal due to high temperature. Overheating can disable the already “tired” rubber, after which it forms cracks and leaks. The membrane inside the working part (between the wax filler and the stem) also suffers from overheating.

If the thermostat breaks down, it begins to respond worse to temperature changes, and then it jams. The thermostat valves may block the pipe leading to the radiator or to the bypass channel, or they may stop in the middle position.

Malfunction signs:

The engine heats up for a long time – the pipe to the radiator is open, the antifreeze is cooled, preventing the engine from warming up.

The engine overheats (arrow is in the red zone) – antifreeze does not get to the radiator.

The engine heats up longer than usual, and under load the temperature rises sharply – the valves are stuck in the middle position, part of the coolant constantly passes through the radiator, but at intense driving this cooling is not enough.

Also, indirect signs of a thermostat failure may be non-working interior heating (the”stove” blows cold air, increased fuel consumption, deterioration of engine dynamics.

The worst consequence of a thermostat failure is engine overheating: in the heat, a few minutes are enough to bring the engine into emergency condition.  But driving with an insufficiently warmed engine affects its resource: wear of parts increases, engine oil works ineffectively.

How to check the thermostat?

  1. Start the engine. Before it warms up to operating temperature, antifreeze should not enter the radiator. Consequently, the pipe leading to the radiator must be cold. If it is warm – antifreeze enters the radiator ahead of time.
  2. When the engine warms up, the coolant should go to the radiator, the pipe should be warm.The engine is warmed up, but the antifreeze does not go to the radiator – the valve is closed.
  3. If the engine is well warmed up (almost to the red zone), the antifreeze should not enter the bypass pipe, but all pass through the cooling radiator. Accordingly, the pipe to the radiator will be hot, and the bypass pipe will be cold.

Another test method recommended by old-school car enthusiasts is to dismantle the thermostat and test it in hot water. Of course, if you wish, you can also evaluate the operation of the device, only you need to monitor the opening temperature of the valves. But if there are complaints about the operation of the thermostat, it is better to simply replace it. Thus timely installed performance cold thermostats 11537586885, 11537509227, 11531436386 for BMW engine n62, n63, n73, n74, s55, s63, m52, m54, m56, m64 with an opening temperature of 90C, will help to significantly save money in the future and solve the BMW thermostat problem.

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How to test radiator fan

Checking the electric fan with an ECU Peugeot & Citroen (PSA) on the car using diagnostic adapters.


For fans with an electronic control unit (ECU) forget such concepts as: first, second and third speed, even in spite of what is indicated in the diagnostic programs. In fans with an ECU there can be more than 100 speeds, since the speed is set proportionally to the pulse PWM signal on the control wire, which can have multiple meanings. By smoothly changing the PWM control signal, you can also smoothly change the fan speed, just as the volume control smoothly changes the volume of the sound. You do not say that you have 2 or 3 volumes in the radio. Such concept as the first, second, third speed can only be used for fans without an ECU, in which the speed is limited by powerful limiting resistors connected to the electric motor using a relay. Or multi-brush motors can be used instead of resistors, in which relays are also responsible for switching various brushes. Let’s say we have a fan without an ECU with one resistor and two relays. We can say about this fan that it has two speeds, each speed is responsible for a separate relay. For the first speed a relay is activated, that connects the electric motor with the resistor. For example, at the first speed the fan consumes 15 amperes with an impeller at 12 volts. When the second speed is activated, the second relay is turned on, which supplies power directly to the motor and it gives maximum speed, for example, 30 Amperes with an impeller at 12 Volts. If a fan without an ECU has 2 resistors and 3 relays, then we can say it has 3 speeds. But in no case is it correct to say that a fan with an ECU has 2 or 3 speeds. The fact that different speeds are indicated in diagnostic programs is ‘echoes of the past’ incorrectly interpreted by diagnosticians. If, for example, we run in the diagnostic program ‘Speed of the electric fan 2’ and connect the oscilloscope to the control wire then we will see that the control signal changes very smoothly and the fan speed also increases smoothly from minimum to maximum speed without any sharp changes.

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Peugeot-Citroen cooling fan replacement (Polish fan)

Yesterday we got a non-working ‘Polish’ fan, which worked only one season and its ‘smart’ brains finally died. We installed ours and the fan started working!

Overview of the “Polish” fan for the PSA.

This is a new fan for PSA, which is made by Poles, as an alternative to the original fan.

The price is lower than the original fan has, but do not be deceived:

  • Firstly, the power of the original, with the same ECU, is 700 watts (50A x 14V) and the power of the ‘Polish’ is only 420 watts (30A x 14V), that is only 60% of the required power. So the ‘Polish’ fan at maximum speed will give out only 60% of the required power. These 40% missing may be the reason for not enough cooling of the engine radiator or air conditioner in hot weather, especially in a traffic jam.
  • In the ‘Polish’ fan the motor is made with sufficient quality, there are 2 ball bearings. But what they finally miscalculated is the electronic control unit (‘brains’). Despite the fact that the ‘Polish’ motor consumes only 30 Amperes instead of 50 Amperes as the original one (at maximum speed with the impeller), the control unit of the ‘Polish’ fan ‘died’ after only one season of operation.
  • In the ‘Polish’ fan a very low-quality solder is used for desoldering the elements. When trying to remove the faulty ECU, a little pressure was put on the connector and it immediately pulled away from the board leaving ‘torn’ marks in the soldering place.

In any case, our ECUs are cheaper than the ‘Polish’ fans and you still have the original fan with a capacity of 700 watts with a 1 year warranty.

Conclusion: The cheap new ‘Polish’ fan is not a worthy competitor for our ECUs.