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New to the forum: first post. I've started getting a coolant level warning on my 2012 C220 on first startup each day, but the coolant level is OK. It doesn't happen with subsequent startups - only the first! I'm wondering if it's a faulty sensor, but can't find any reference to a similar issue. Anyone else experienced this?
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Wow! Glad you posted this. I am experiencing the same thing for the first time on my 2015 SL400 and was wondering, "What the heck?" It has been cold (20°-45°F) when this happens, but on inspection, the fluid lever is normal. After a minute or so, the message goes off and there is no stored message. I may ask the service manager at the dealership, but of course, they will want to check things out. I'm going to scan for stored DTCs and will post back here.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Interesting this is happening on different models and different years. I will still check, maybe before starting the car, but am not losing sleep over it.
Maybe try adding a little coolant, may just be below the level and when it warms it expands. Thats what I would do. I have a jug of the Zerex 50/50 coolant on hand. Napa usually has it for $14. The blue is G48 and I think the pink is G40.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Took another look and, low and behold, we have two reservoirs! Whoda thunk that? And, in the one that has the level sensor, the coolant level is actually low.
Wow! Glad you posted this. I am experiencing the same thing for the first time on my 2015 SL400 and was wondering, "What the heck?" It has been cold (20°-45°F) when this happens, but on inspection, the fluid lever is normal. After a minute or so, the message goes off and there is no stored message. I may ask the service manager at the dealership, but of course, they will want to check things out. I'm going to scan for stored DTCs and will post back here.
I should have said this has only started happening since the weather turned cold ...... The car lives outside and it's been down to freezing some nights
New to the forum: first post. I've started getting a coolant level warning on my 2012 C220 on first startup each day, but the coolant level is OK. It doesn't happen with subsequent startups - only the first! I'm wondering if it's a faulty sensor, but can't find any reference to a similar issue. Anyone else experienced this?
Same thing for me on a 2019 GLE300 (W166). Started happening about 6 weeks ago. Initially, the secondary intercooler coolant expansion tank was actually low, and I filled it with Zerex. But the problem still kept happening, and I added a little coolant to the main tank even though it wasn't below the line, but the problem still happens.
The DTC for this issue is P25567B (on my W166 car) and it is stored in the SAM module. That code really doesn't help though, except perhaps to confirm that the problem isn't something more serious than coolant level.
I really would like to know how to determine the proper fill level. The white line on the tank isn't labeled LOW or MAX, so I can only presume it means LOW and I don't know how high to fill to MAX. I don't want t overfill!
I also actually don't see any coolant level sensor or wiring plugged into the expansion tank (nor anywhere on the parts diagram), so I don't know how this car alternatively determines coolant level, if the issue is actually with the sensor.
I cannot figure out where the "fill level" in my car is. I dont see any clear mark inside the tank to go off of and ive looked. I just filled it so its above the white part of the bottom of the tank. The operators manual says how to check, but im not seeing what its referring to.
I topped the fluid up once previously just to bring it above the white part looking from the outside. I bought a jug but I only added maybe 1/4 liter. Then i recently drained and replaced the coolant during oil filter housing gasket replacement.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Fill the main expansion tank when cold (like first thing in the morning) to where the level is at where the black top meets the white transparent bottom. You should be good. If overfilled, the cap has a relief valve that will allow excess coolant to escape.
NOTE: Do make sure you are using a 50/50 mix to top off and not just straight coolant. Proper cooling and corrosion protection is at 50/50 with NO MORE THAN 55% coolant/45% water. Always use distilled water.
Last edited by JettaRed; Dec 24, 2023 at 08:23 AM.
Checked inside the tank, and while I don't quite have a black tab sticking out like #3 from the manual page (different model), there is still a small black section along the lower rim of the opening that I guess is meant to indicate full level.
I added more coolant, although not quite all the way up to the black to be cautious. The low coolant indicator went off without me ever having started the engine, so Low Coolant level warning was probably correct all along. Keeping my eye on it now that it doesn't fall below the threshold again anytime soon!
Important to note that the secondary coolant reservoir tank near the engine in the newer cars (a separate coolant system for just the intercooler I believe) currently has no low coolant sensor or warning indicator at all! I initially was only looking at that since it was very low when this error indicator first appeared, but it was actually the main engine coolant reservoir that set off the alarm.
Thats why I originally wrote to add a little coolant. If the low level warning is coming on when cold then goes out when the engines warm the sensor seems to at least be functioning, or it would stay on im guessing. Do the most obvious thing, which is to add coolant.
Mine only has the one coolant reservoir and it has a sensor on the bottom, im looking at others that have two tanks and it does seem at least the main tank has a sensor also. I have no idea how the two tanks work, if they are connected to each other.
You're right! I just took a mirror to peek underneath the engine coolant expansion tank, and there is indeed a wire plugged in to the bottom like you pictured.
Not sure where that wire comes from, but mystery solved, the coolant level sensor is integrated into the expansion tank and not replaceable or sold as a separate part anymore.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Turbo cars have two coolant circuits--main circuit for the engine and low-temperature circuit for the intercooler and turbos. They are NOT connected. And the turbo circuit does not have a low level sensor as far as I can tell. If it does, it's not in the expansion tank. The main circuit is the one we've been discussing with the black top and white, transparent bottom.
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