I have a 2023 Solaris, and this error keeps popping up for the third month now. The diagnostician said the thermostat is fine, but the coolant temperature sensor might be glitchy. Is this a common problem on this generation or is it something specific to mine?
On the new generation Solaris this is really a common thing. I've driven a lot of those cars myself in logistics, and I've run into this error more than once - in most cases it's the coolant temperature sensor that's to blame, not the thermostat itself, usually it's either a bad contact or the signal gets disrupted. If the diagnostician has already checked the thermostat itself and it's fine, then it makes sense to replace the coolant temperature sensor - it's a dirt cheap repair compared to other problems, and it often fixes it on the first try.
This error really does show up on new-generation Solaris, and it's often the electronics that's to blame, not the thermostat itself. P0128 pops up when the cooling system doesn't warm up to the required temperature within the allotted time frame, and the coolant temperature sensor plays a key role here - if it glitches and gives wrong readings, the ECU thinks there's a heating problem when everything's actually fine. On the 2023-2024 Solaris, people have noticed this sensor is sensitive to voltage spikes and contact oxidation, especially if the car is driven in the city with frequent on-off cycles of all the electrical equipment.
Before heading to the service center, I'd recommend checking the temperature sensor contacts first - it's usually located near the thermostat housing, and sometimes just reconnecting it helps. If that doesn't work, you'll probably have to replace the sensor itself, it's not an expensive part. While you're at it, ask the diagnostician to read the direct sensor values at different engine temperatures using a scanner - if they jump around or look weird, then it's definitely the sensor. I've personally seen similar glitches get fixed just by replacing the sensor, so don't rush straight to warranty, might be worth trying it yourself.
My friend ran into a similar situation with her 2023 Solaris, and yeah, it really is often the temperature sensor rather than the thermostat itself. In her case the problem was fixed after replacing the coolant temperature sensor - the error stopped showing up. If the diagnostician checked the thermostat mechanism and it's working fine, then it makes sense to try the sensor, especially since it's cheaper than troubleshooting further. On the new generation Solaris these electronic glitches aren't uncommon, so you're not alone.
I know that problem) this error really is a common thing on modern Solaris buses. someone already correctly mentioned the sensor above - that's really a frequent cause. the thing is P0128 gets triggered when the ECU doesn't see normal engine warming, but why that happens - there could be several reasons here. the coolant temperature sensor is sending wrong signals, the electronics thinks the engine isn't warming up, so the error light comes on. the thermostat can be completely fine in this case, so the diagnostician was right
there could also be an issue with contact quality in the sensor connectors or wiring, oxidation happens sometimes. if the engine is actually warming up normally and the fan kicks in like it should, then most likely it's the sensor itself or its electrical circuit that's acting up. try at least checking the visual condition of the sensor connector under the hood, sometimes just reconnecting it or cleaning the contacts helps. if that doesn't work, you'll have to replace the sensor, it costs next to nothing and takes like 15 minutes of work
seems to me you should also make sure the cooling fan is turning on properly and the engine is actually warming up like it should. if the cooling is actually fine in practice, then go ahead and replace the coolant temperature sensor - that's the most likely fix for your situation
That happens a lot on new Solaris models, and the diagnostician is right - usually it's just the coolant temperature sensor acting up, not the thermostat itself, because the electronics in this generation aren't super reliable. Try replacing it, it's dirt cheap, and the error should go away.
Guys, looks like you're all hitting the nail on the head with the coolant temperature sensor 😊 I'll add my two cents - on 2023 Solaris models, this error really does pop up often, and nine times out of ten the problem is actually the coolant temperature sensor itself, not the thermostat. The electronics on newer generations are more sensitive to signal spikes, and even a slight sensor contact issue can trigger a false alarm. The thermostat itself works fine in this case, but the engine control unit gets weird data and can't properly regulate the warm-up process.
My advice - don't put off replacing the sensor. It's a simple procedure, maybe a couple hours at the shop, and won't break the bank. Check if there's any oxidation on the sensor connector contacts - sometimes a good cleaning with alcohol helps 🔧 If cleaning doesn't help, just swap the sensor for an OEM one or a quality equivalent. After replacement, the error should either disappear completely or stop showing up constantly. By the way, remember to clear the error codes after the work, otherwise it might stick in the memory from the previous cycles.
The sensor is definitely a common cause, but before replacing it, it'd make sense to check the wiring and contacts first - I've seen a few cases where oxidation in the sensor connector gave exactly the same error, but the sensor itself was fine. Ask the diagnostician to visually inspect the coolant sensor connector, maybe that's the issue, and then cleaning the contacts would be cheaper than replacing it.
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