Cooling fan constantly running

The situation when cooling fan runs constantly can be caused by several reasons: failure of the coolant temperature sensor or its wiring, breakdown of the fan start relay, damage to the wires of the drive motor, "glitches" of the electronic control unit ICE (ECU) and some others.

in order to understand how the cooling fan should work correctly, you need to know what temperature is programmed in the control unit to turn it on. Or look at the data on the fan switch located in the radiator. Usually it is within + 87 ... + 95 ° C.

In the article, we will consider in detail all the main reasons why the internal combustion engine radiator cooling fan works not only when the coolant temperature reaches 100 degrees, but always with the ignition off.

Reasons for turning on the fan	Conditions for inclusion
Failure of DTOZH or damage to its wiring	Started internal combustion engine in emergency mode
Shorting the wires to ground	Running internal combustion engine, when contact appears / disappears, the fan may turn off
Short circuit of wires to “ground” at two DTOZH	Running internal combustion engine (first sensor) or ignition on (second sensor)
Faulty fan enable relay	Started internal combustion engine in emergency mode
"Glitches" ECU	Different modes, depends on the specific ECU
Heat dissipation of the radiator is disturbed (pollution)	With the engine running, during a long trip
Faulty freon pressure sensor	When the air conditioner is on
Low efficiency of the cooling system	When the engine is running

Why does the cooling fan keep running

If the internal combustion engine fan is constantly running, then there may be 7 reasons for this.

Coolant temperature sensor

• Failure of the coolant temperature sensor or damage to its wiring. If incorrect information goes from the sensor to the ECU (an overestimated or underestimated signal, its absence, a short circuit), then errors are generated in the ECU, as a result of which the control unit puts the internal combustion engine into emergency mode, in which the fan “threshes” constantly so that there is no overheating ICE. To understand that this is precisely the breakdown, it will be possible by the difficult start of the internal combustion engine when it is also not warmed up.
• Shorting wires to ground. Often the fan is constantly running if it frays the negative wire. Depending on the design of the internal combustion engine, this can be in different places. If the motor design provides for two DTOZH, then if the "minus" of the first sensor breaks, the fan will "thresh" with the ignition on. In case of damage to the insulation of the wires of the second DTOZH, the fan runs constantly when the internal combustion engine is running.
• Faulty fan enable relay. In most cars, the fan power consists of a "plus" from the relay and a "minus" from the ECU in terms of temperature from the DTOZH. "Plus" is supplied constantly, and "minus" when the operating temperature of the antifreeze is reached.
• "Glitches" of the electronic control unit. In turn, the incorrect operation of the ECU can be caused by a malfunction in its software (for example, after flashing) or if moisture gets inside its case. As moisture, there may be a banal antifreeze that got into the ECU (relevant for Chevrolet Cruze cars, when antifreeze enters the ECU through a torn throttle heating tube, it is located near the ECU).
• Dirty radiator. This applies to both the main radiator and the air conditioner radiator. In this case, often the fan runs constantly when the air conditioner is on.
• Freon pressure sensor in the air conditioner. When it fails and there is a refrigerant leak, the system “sees” that the radiator is overheating and tries to cool it with a constantly on fan. For some motorists, when the air conditioner is turned on, the cooling fan is constantly running. In reality, this should not be the case, since this indicates either a clogged (dirty) radiator, or problems with the Freon pressure sensor (Freon leak).
• Low efficiency of the cooling system. Breakdowns can be associated with a low coolant level, its leakage, a faulty thermostat, pump failure, depressurization of the radiator cap or expansion tank. With such a problem, the fan may not work constantly, but for a long time or turn on frequently.

What to do if the cooling fan is constantly running

When the internal combustion engine cooling fan is constantly running, it is worth looking for a breakdown by doing a few simple diagnostic steps. The check must be performed sequentially, based on the most likely causes.

Cleaning the radiator

• Check for errors in the ECU memory. For example, error code p2185 indicates that there is no “minus” on the DTOZH, and a number of others (from p0115 to p0119) indicate other malfunctions in its electrical circuit.
• Check the integrity of the wires. Depending on the design of the motor, individual wires associated with the fan drive can be damaged (usually the insulation is frayed), which causes a short circuit. Therefore, you just need to find the place where the wire is damaged. This can be done either visually or with a multimeter. As an option, insert two needles into the contacts of the chip and close them together. If the wires are intact, the ECU will give a motor overheating error.
• Check DTOZH. When everything is in order with the wiring and power supply of the sensor, then it is worth checking the coolant temperature sensor. Along with checking the sensor itself, you also need to check the contacts on its chip and the quality of the chip fixation (whether the eyelet / latch is broken). If necessary, clean the contacts on the chip from oxides.
• Relay and fuse check. Check if power comes from the relay to the fan using a multimeter (you can find the pin number from the diagram). There are times when it "sticks", then you need to change it. If there is no power, check the fuse.
• Cleaning radiators and cooling systems. If the base radiator or air conditioner radiator is covered with debris, they need to be cleaned. A blockage of the internal combustion engine radiator can also form inside, then you need to clean the entire cooling system with special means. Or dismantle the radiator and wash it separately.
• Check the operation of the cooling system. The fan can work continuously with low efficiency of the cooling system and its individual elements. Therefore, it is advisable to check the cooling system, and if breakdowns are detected, repair or replace its parts.
• Checking the freon level and the operation of the refrigerant pressure sensor. To carry out these procedures and eliminate the cause, it is better to visit the service.
• ECU check is a last resort when all other nodes have already been checked. In general, the control unit must be dismantled and its housing disassembled. then check the condition of the internal board and its elements, if necessary, clean it with alcohol from antifreeze and debris.

In summer, driving with the fan constantly on is undesirable, but acceptable. However, if the fan turns constantly in winter, it is recommended to diagnose and fix the breakdown as soon as possible.

Hack and predictor Aviator

Most often, the radiator cooling fan turns constantly due to a short circuit in the starting relay or its wiring. Other problems are less frequent. Accordingly, diagnostics must begin with checking the relay, wiring and the presence of errors in the computer memory.