Where is the cooling level sensor?

[Redd]

Either coincidentally (sure) or because something was knocked astray when the brakes were flushed a few weeks ago, I have gotten a bogus SHUT ENGINE, CHECK COOLANT LEVEL warning on the dash eight times now. The first time, the day after that service.

VCDS tells me the coolant is a steady 99C, which seems fine, and the dash gauge is sleeping in the usual "halfway" position. And that bottle is absolutely full with the original red coolant which Audi presumably topped up during this most recent service, or in the past.

But as I look at the coolant bottle, I see two small black rubber hoses on the top, presumably the radiator connection and the drain, and one heavy wrapped hose connected under the bottle, where it mounts to the frame. That hose is hot, so I'm guessing it is also a coolant hose, not just a fat harness.

But I don't see anything like a simple level sensor, a float perhaps? Something that might simply have come out of position or failed, and that can be easily tested and replaced to get rid of the bogus "I'm sorry Dave, the core is melting down now." warnings.

Anyone ever met that cooking level sensor before? I'm afraid to ask, is it perhaps located not on the bottle but reading the level from elsewhere??

[elscotto80]

There is one on the water pump another one elsewhere - I think near the oil cooler on a coolant pipe or near the heater core pipes (sorry - can't recall).

Maybe take it back to the shop and be like, yeah...this just started after I picked it up from you fellas...

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[Redd]

The shop: "That's very unlikely but we can check. There will be a $200 diagnostic fee if we didn't knock anything loose."

Apparently there is one in the reservoir, it just looks like a vacuum hose instead of a conventional wire harness going into it.

[old guy]

The coolant level sensor plugs into the bottom of the reservoir closer to the back of the car. You can see it clearly below. Make sure yours is plugged in.

[Redd]

Interesting. I didn't see any wiring back there but will check again when I can run finger in a cold engine bay.
I was also shown an (ERWIN?) snapshot that claims the sensor leads are the top front "hose" that comes off the reservoir.
Reading glasses, flashlight...I wonder if part of this is year-specific?

[old guy]

The "sensor" is nothing sophisticated. It is simply two vertical wires that run parallel up from the bottom of the reservoir. As the coolant level decreases the current flow between the two wires decreases. Once it goes below a threshold value you will get a low coolant warning. If it is unplugged the ECU assumes the reservoir is empty and you get the same warning.

[Redd]

Thank you Old Guy! Even more important to know how it works.

With the aid of good light and a cold engine, I saw they indeed had tucked some kind of connector over the rear "leg" of the coolant reservoir. It was and is firmly connected and dry, as best I can tell. I manage to peek at a short bit of brown and green lightweight wire down there, but almost the entire length looks like it was wrapped in cheesy black friction tape, running up maybe 8" to tuck alongside what looks like a harness connection to the ABS body and a red switch(?) on the inboard side of that. Presumably the switch kills the ABS, but even if the shop monkeyed with that to do the brake flush...it should have affected that carefully hidden wire run.

Am I pressing my luck to ask if you know how that connector releases? I have, I will admit, more than once broken a pack-con when trying to disengage it. Does it squeeze or unclip or...I presume I don't just try to tear it off the bottom of the reservoir. (Well, that might FEEL good.(G)

I'm afraid to even think of where else that wiring harness might go to, and where the next place to check for a loose connection might be.

[old guy]

The two wire clip is secured the same way as the coil pack harness. Push the connector in tighter, press down on the release lever and pull the connector off. It should look like this one:

[doc_oc]

For easier access, take the 2 Phillips screws out at the top of the coolant tank and pull it up slightly. You'll be able to see better what you're doing there.

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[Redd]

Thank you, gentlemen!

Coil pack connector? I'm a spark plug guy! But I think that means to compress the smaller rectangular area, that it is a bit which will compress in (just form one side) and then allow a release? I usually grab a plier or forceps to do the compressing, it beats sticking my finger in the pencil sharpener to make it small enough.

Removing the two Philips to get a bit more slack certainly is a "D'Oh!" Homer Simpson Moment. Yeah, being able to simply get a line of sight on that will help.

As the fluid looks a bit like ruby red grapefruit juice (obviously not transparent), is that the normal color I should expect to see in there? Or a sign that perhaps they topped it off with the wrong fluid, the day all this business started? How could I know, short of "Oh, just change all the coolant" ?

[Novarider]

The proper coolant is pink/red. No idea if you can see through it tho I've never checked.

[doc_oc]

Pink is the right color. But it should be transparent. Not milky and no particles in suspension.

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[Redd]

Sounds like the right (same) stuff. Put 100+ mile son the highway today, no complaints from the engine. If I'm lucky that means my gerfingerpoken on the sensor wires made them happy again, at least for the day. But once I remember to get a turkey baster, I'll empty out the bottle and swab down the sensor rods anyway.

Can I rashly assume that the car will also independently flash an "ENGINE OVERHEATING" warning, if the coolant in fact does go low?

They used to say the new coolants were "permanent". How long does Audi say this stuff is good for? Or, just use a coolant tester?? Last time I went to an auto parts chain to see if they still made "water pump lubricant etcetera" additive for coolant, they looked at me like I was from Mars. Or, really really old. It used to be so simple to just top up the additives if the coolant still tested good! And now we're supposed to dump gallons to accomplish the same thing as much higher costs?