Low Coolant Light but plenty of coolant in the reservoir?

[pandapod]

Another month, another issue...LOL. I'm wondering if anyone can troubleshoot an issue with my coolant light. This popped on the other day while driving for maybe 10 minutes. Car temperature was right in the middle where it usually is, and I've never seen it get above this point. Drove 5 more minutes to my house and shut the car off. The next morning i started the car and of course the light was still on, beeping at me, so i added coolant to the tank. Before adding it, i realized i was right in the middle, so i was unsure why it was beeping at me but i added more anyway. So after i added the coolant, slightly above the "max" line, i started it up again and got the same warning light.

Needless to say, i'm a little scared to drive it in the event there's some sort of major failure (car runs great still, from what i can tell). Is there some sort of low-level sensor i can look for and possibly replace? What would cause this error other than actually having low coolant? There shouldn't be a leak anywhere as i have plenty of coolant.

As for things that may have changed recently - i have noticed that on some days it takes quite a while for my engine to get warm. Not just on colder days either. Typically the car gets to the middle on the engine temp gauge in about 10 minutes. Lately, i've seen it only get to the 1/4 mark after about 10 minutes and may not get up near the 1/2 mark until i'm almost home from my 30 minute commute. I was wondering why it would take this long. This, and a random CEL from last week, have me wondering. The CEL went away after a couple days so i wasn't able to read it, and i do not have a Ross-tech to read what has been stored.

Any help is greatly appreciated, thank you!

[JimmyBones]

There is a low level sensor in the bottom of the coolant tank. Take the one screw out for the coolant tank, then lift the coolant tank out of the tab retainers, and check that it is plugged in. If it is plugged in then spray the pins with some electrical contact cleaner and plug it back in. Check that the warning goes away before you put the coolant tank back in and screw it down. If it is plugged in and spraying the pins with cleaner doesn't help then you probably need a new coolant tank. Also check if there are cracks along the bottom of the coolant tank because as the plastic ages it discolors into a yellowish clear and it starts to crack along the bottom from the engine heat.

As far as the engine heating up goes. When it is colder out it takes longer for the engine to reach operating temperature, especially if you do a lot of stop and go rush hour traffic. You live up north where it is going to be colder outside ambient temperature wise than people like me farther south. If you are really worried about then you can replace your coolant temperature sensor, the o-ring, and the plastic C-clip. It isn't that difficult to do other than you can't see much because it is on the rear coolant pipe behind the engine.

[Wiggler]

As for things that may have changed recently - i have noticed that on some days it takes quite a while for my engine to get warm. Not just on colder days either. Typically the car gets to the middle on the engine temp gauge in about 10 minutes. Lately, i've seen it only get to the 1/4 mark after about 10 minutes and may not get up near the 1/2 mark until i'm almost home from my 30 minute commute.

Sounds like your thermostat is sticking/stuck (in open position). If it takes too long for the engine to warm up the coolant idiot light comes on.

http://www.audizine.com/forum/showth...n-Cold-Weather

[pandapod]

thank you both for your replies. I checked out the low level sensor and the plug was connected, but there is noticeable discoloring and dark looking stuff around the sensor, so i've gone ahead and ordered a new expansion tank with the built-in sensor. Hopefully that fixes my issue, or i will move on to the next area.

Just to expand on my issue, as soon as i start the car the fan comes on, maybe because the car thinks it's overheating. The fan remains on for over a minute once the car is shut down. I was thinking about ordering the coolant temp sensor if my problem persists: https://www.ecstuning.com/Audi-B7_S4--V8/ES2535452/ however i can't seem to find where this is located or how to get to it. If anyone knows how to change this, a link would be greatly appreciated. If this job takes awhile, perhaps replacing the thermostat first would be a better idea.

[pandapod]

Update: i installed the new coolant tank and that did not fix my problem. Went to the mechanic today and he mentioned there were A LOT of faults/error codes stored in my computer and that one of them was tricking this light. They cleared everything and I appear to be good to go. I'll stop back in next week for them to check if any of the codes came back.

A little upset I spent $60 on the new coolant reservoir for nothing, but it sure does look nice in my engine bay! The old one was so discolored, this new one makes my engine bay look brand new. Now i have to replace the windshield wiper reservoir so they match...

[jakeoboy67]

Update: i installed the new coolant tank and that did not fix my problem. Went to the mechanic today and he mentioned there were A LOT of faults/error codes stored in my computer and that one of them was tricking this light. They cleared everything and I appear to be good to go. I'll stop back in next week for them to check if any of the codes came back.

A little upset I spent $60 on the new coolant reservoir for nothing, but it sure does look nice in my engine bay! The old one was so discolored, this new one makes my engine bay look brand new. Now i have to replace the windshield wiper reservoir so they match...

get the B6 side engine covers to hide that reservoir and make your engine bay nicer

[VinnysS4]

get the B6 side engine covers to hide that reservoir and make your engine bay nicer

do they fit both the B6 and B7? i have a 2005.5 b6/b7 that id like to get the covers for

[S4Newbie]

It's the coolant temp sensor, I have had this issue already and changed the expansion tank as well😭.thermostat is most likely fine, and I have no idea why the temp sensor affects the coolant level light but it does, it also affects the temp gauge in your cluster which is why it takes longer to get to the normal (middle) position.