Sudden drop and fluctuation of the temperature gauge

Hello, the following problems have occurred with the temperature gauge in my 2012 model 206+. Has anyone had a similar problem? What could be the cause? It was not possible to get it fixed in the workshop. I made an appointment with the service for Friday. If anyone has an idea about this, I still need your help. The temperature gauge suddenly drops from 90 ° C to 60 ° C (the lowest point) while driving normally. It mostly does not occur in the city, but on the ring road / at high speed. Even though the temperature on the gauge drops, the heater blows hot, meaning the engine is actually hot. The STOP light or overheating warning does not come on. What has been done: The thermostat has been replaced. The temperature sensor (coolant temperature sensor) has been replaced. Despite this, the problem persists. When the sensor plug is unplugged: The temperature gauge peaks, the STOP word appears, the fan runs → protection mode is activated. Final Observations: In the city: Generally, there is no problem, the temperature remains normal. On the ring road (above 80-90 km/h): The gauge drops suddenly. Sometimes it fluctuates from 90 to 80-85 °C but does not stabilize. The day after the thermostat was replaced, it gave an Antipollution Fault warning and the fault light came on.

Hello. If I were writing this, I would have written the same text except for the sentence, "The day after the thermostat was replaced, the Antipollution Fault warning and the fault light came on." We're experiencing the same problem. We've spent a lot of time working on it, but the conclusion is that the source of the problem is the "brain." But no intervention has been made yet. I'm really curious what the service department will say. I wish you all the best...

The fault light went off on its own today. That's probably due to the apparent temperature drop. Because the temperature dropped from 90°C to 60°C, the ECU senses cold and increases fuel consumption. The sensor on the exhaust outlet is triggering a rich fuel alarm because of this. I researched and came to this conclusion. It seems likely that it's the ECU, the brain, but I found it unlikely. There was no problem with the connection to the electrician, and the temperature readings from the ECU and the display were the same. When the display dropped, the temperature in the ECU also dropped. A multiple-site ECU fault would result in a permanent fault. They stated that it might appear and then disappear. It's also possible that different sensor faults can occur in succession. I suspected a disconnection in the wiring, but I haven't been able to resolve this issue in the industry where I live. I can't get experts to do the work. One says one thing, the other says another. I've already messed with the thermostat and the water pump for nothing. So, I'll take it to the service center on Friday. I hope they find the problem and it's not the brain. If we buy an original, the online price says around 20,000, so I don't know what the service center would charge. I have no idea how to fix it. My problem is in this video: https://youtube.com/shorts/G4--8qDCD7c?si=G85-wXhLqH5XMrPP. I wonder how they came to the conclusion that the problem is in the brain? Onlinewolf2025-10-01 18:52:49

"There was no problem with the connection to the electrician's ECU, and the temperature data going to the ECU was the same as the data on the display. When the display dropped, the temperature in the ECU also dropped." The same thing happened to me. There wasn't much definitive information about the ECU. However, all electrical possibilities were examined. (Of course, after changing the thermostat and the sensor) And the technician said that the only thing left was the ECU. Otherwise, we don't have any data other than this approach. Maybe we can get a comment from someone who has experienced a similar problem and found a solution on the forum.

Meanwhile, there is only information that the brain cannot be repaired, it can either be original or a replacement.

I updated my post later; I don't know if you saw it. I added the video. There's speculation it might be a cable issue. I hope the service team will have a solution by Friday. But as you know, when they can't find a problem in one place, they send me somewhere else. They sent me to electricians, motorists, and electricians. We'll see what happens. I'll let you know if I get a solution on Friday.

While I was walking around the industry today, I saw a lot of repairmen who said they do brain repair, but I don't know, so I didn't ask. Onlinewolf2025-10-01 18:57:18

I would be happy if you could let me know... Similarly, if there is any development, I will share it. Good luck to you... Saramago2025-10-01 19:21:28

I went to the authorized service center today. They told me there was no mechanical problem, that the problem was between the instrument cluster and the computer, and that I should see a repairman for both the instrument cluster and the computer. He said the fan had kicked in on time, that there was no problem with the vehicle, and that the display was just misleading. I just spoke with the technician and the indicator technician, and he told me to come back tomorrow for a checkup. Keep trying. I hope you get a solution, at the cheapest price.

We're getting almost the same answers. In addition to mine, there's no problem with the display. I also made an appointment with a "brain specialist" on Monday, as they said they needed to take a look. Of course, the problem here is that this issue may not be apparent during their inspection process. But it can occur at any time while the user is using the vehicle. I'll keep you posted on any developments, thanks.

They said there is no problem with electronics...

I believe a corrective action cannot be taken without replacing the temperature sensor with the original. I've ordered it. None of the replacements have the same characteristics as the original. Therefore, there's a possibility they might not be sending accurate information to the brain. I've come to the conclusion that a solution cannot be achieved without eliminating this detail.

I went to an electronics store. The car has been sitting for three days. I fixed two wiring issues (one socket, one cable). He said there was a fault with the display and said he fixed that too. He tested it and said no problem. I took it back, and the same thing happened, so I took it back. After that, the car sat down again. The fan relays were heavily oxidized. I couldn't find the original ones, so I cleaned them. I bought them today. It seemed fine, but when the car warmed up, it did the same thing again. I also ordered two original fan relays. I'll have them installed in two days. I don't know if anything will change. But in the process I've described, 8500 TL wasted. If the temperature sensor is original, please let me know.

I changed it today. The same thing happened again. I removed the battery terminal. After waiting a while, I replaced it. So far, everything is going well. We'll see if it happens again.

https://www.reddit.com/r/MechanicAdvice/comments/1m0jfqn/peugeot_206_2011_temp_gauge_drops_after_warmup/ I found the same issue here, but unfortunately there was no solution. I think if it hasn't been doing this for so long, it probably won't do it. How often did it do it before?

I've gone through everything you mentioned above, too. Relays, cables... so no changes whatsoever.

[QUOTE=Onlinewolf]https://www.reddit.com/r/MechanicAdvice/comments/1m0jfqn/peugeot_206_2011_temp_gauge_drops_after_warmup/ I found the same issue here, but unfortunately there was no solution written. I think if it hasn't been doing it for so long, it probably won't do it. How often did it do it before?[/QUOTE] It says internal error, I couldn't read it. I've never experienced anything like this before.

No Reddit, if it was doing it frequently when it was malfunctioning, I think it has been fixed if it hasn't done it in this period. Onlinewolf2025-10-08 19:34:11

I'll try it for a while and let you know...

I'm waiting for your good news.