Skoda Octavia Mk1 1.6 AVU/BFQ Thermostat Only Opens at Max Heat Setting—Why?

Hello,

I own a Skoda Octavia Mk1, 2002, 1.6 petrol, engine code AVU, BFQ.
While waiting in traffic last year, I noticed the temperature was over 90 degrees. I pulled over, opened the hood, and noticed the fans weren't spinning. If I turned on the air conditioning, they would spin. During the diagnosis, I noticed that the thermostat, which is controlled by the ECU, only opens with the cold/hot potentiometer at maximum heat. If the potentiometer is at minimum cold or at an intermediate position, the thermostat does not open. Basically, the coolant reaches 95 degrees, the thermostat opens, it starts flowing through the radiator, the sensor on the radiator registers the temperature increase and at around 70 - 80 degrees the radiator temperature, the fans start rotating at second speed.
Before, it would turn on the fans at 90 degrees, with the first speed. I replaced the fans and the fan control module and the same thing happened.
I can't use the air conditioning in such conditions.
AI: Have you checked or replaced the coolant temperature sensor(s) on the engine? If so, did you notice any change in the thermostat or fan behavior?
Yes
AI: Have you scanned the car for any fault codes (using OBD diagnostics), and if so, did any codes come up related to the cooling system or sensors?
Yes

Maybe the fuse 1 of the ventilator fuse on the battery is faulty. No. 3 and 6

Hello,

They made a very big mistake when they implemented the ECU controlled thermostat. If it was classic, everything would be ok. The problem is with the thermostat, why does it only open with the knob at full right. If I turn on the air conditioning, the fans spin at speed 1. So it wouldn't be a fuse issue. First the thermostat opens, allowing the coolant to flow to the radiator and then the fans start. They have no reason to start if the coolant in the radiator has a temperature of 30 - 40 degrees.

On this car the thermostat is not controlled by the ECU in any way. It's a normal thermostat that has full opening at 87st as I recall and it has nothing to do with the position of the potentiometer from the heater. You may have the wrong thermostat fitted.

Hello,

My car has a thermostat controlled by the ECU, it doesn't have a switch on the radiator to control the fans. The thermostat has two wires that go directly to the ECU and without its command it won't open. It doesn't open even at 115 degrees. It has a paste, a wax inside and the ECU controls its heating and thus it opens.

Sorry you are right , I checked and there were 2 types of thermostats , the regular one and the extended one with control. Maybe try replacing the thermostat with another piece that works.

Hello,

Replaced without any effect. I'll do more research on this way of managing the thermostat.

Added after 9 [hours] 5 [minutes]:

Exactly what I was mentioning. It has to do with the temperature control knob.
There are 5 factors that contribute to the degree of thermostat opening, along with ABS. Now I know where to check.