cnelson14

Hello,

I was driving back from the shop a couple days ago after getting my driver side window regulator replaced. After about 20 minutes of driving the dash board computer beeped at me and flashed the coolant warning until I got home.

After letting the car cool down I checked the coolant level and it was at minimum. I filled the reservoir up with a 50/50 mixture of the Audi antifreeze and distilled water.

The next day I started on my trip and within 30 seconds of ignition the coolant warning came on again.

The manual listed two reasons why the warning was being sounded.
1. Coolant level low
2. Coolant temperature to high

I know the coolant temperature wasn't high because the warning came up after a night of sitting in the garage.

I know the coolant level isn't low anymore because I filled up the reservoir to a little below max.


Seeing that nothing was wrong I drove to and from work (30 miles away) in the southern Californian heat and traffic. The coolant warning stayed on, but the coolant temperature gauge did not ever run hot. So I don't think anything is physically wrong.


I can think of three problems.
1. Coolant sensor is stuck below minimum
2. Coolant sensor is broken
3. Electrical problem

Today I tried to jiggle (and then whack) the reservoir to see if I could unstick the sensor. That didn't work.

I also tried unplugging the connector under the reservoir. But the warning still came on.


So do you guys have any other suggestions? Should I buy a ~70$ sensor. And how hard would it be to install the sensor?

Thanks,
Cee Nelson

RussB

The sensor is part of the reservoir and both are replaced as a unit. Did you succeed in unplugging the harness connector from the coolant level sensor? If so, and the coolant level light remained on, there's a problem with the wiring.

More likely, the sensor's contacts have welded themselves closed. I've had it happen, and fixed the problem by replacing the reservoir (with integral level sensor).

BTW, why was the coolant level low? Got a coolant system leak? These cars have minimal reserve coolant, and in hot weather it's important that all coolant leaks are stopped, so that the system may operate at 14 PSI. To locate leaks, I use a homemade reservoir cap with a Schraeder valve and hand pressurize the cooling system while the engine's cold, which makes poking around while looking for coolant leaks safe and comfortable.

Best of luck from (very hot) south Florida.

cnelson14

Thanks for the reply.

Is it possible to remove the sensor from the reservoir? If so how does one do it, either by unscrewing or pulling? If I do do this, is it possible to reinsert the existing sensor and not have any leaks?

As for the leaks in the coolant system I don't ever see coolant under my car. It is usually garaged during the week and most of the time only gets taken out for fun runs on the weekend. Although I will look more carefully to see if the coolant is puddling inside the engine compartment.

Thanks,
Cee Nelson

RussB

I forget why, but after examining the reservoir I submitted to Audi's wish that the reservoir and sensor be replaced as an assembly.

RussB

I've found that hot coolant, which may be under pressure (up to 14 PSI above atmospheric pressure) when it's contained, evaporates quickly when it escapes to 0 PSI above atmospheric pressure -- so it's difficult to see and certainly won't form a puddle.

I search for coolant leaks only when the engine and coolant are at room temperature by artificially pressurizing the coolant system. That way the escaping coolant remains in a liquid state and is easily found.

Donny Sandau

You can buy a new coolant tank complete with sensor from Autohaus.com for $27.26

cnelson14

Thanks for all your help so far Russ.

I have been fiddling some more with the reservoir trying to get the coolant light to go off. I finally decided to call up the Audi parts dealer. I might purchase a ~55$ reservoir with sensor included.

One thing the dealer suggested, to see if the sensor is broken, was to pull out the connector underneath the reservoir and complete the circuit with some spare wires.

The thinking was, the sensor inside the reservoir completes the circuit when the fluid level is above minimum. But perhaps the bridge to complete the circuit is stuck or malfunctioning. So completing the circuit before the sensor would eliminate the warning and prove that the sensor was the problem.

Tried that and no luck still.

Do you think this test gave any useful results, or could our thinking regarding a completed circuit be incorrect?

I'm at the point of buying the new reservoir, and if that doesn't work then I will just have to live with the light.

Thanks again,
Cee Nelson

MrGoodbytes

Could be faulty IC?

RussB

I'm looking at a schematic now. The level switch is SPST (single pole single throw) and is drawn schematically as a normally open switch. I suspect that an alarm is displayed when the contacts close. (Which is the opposite of what you and the dealer guessed.)

If this is the case, then removing the connector from the switch will extinguish the alarm. Shorting the switch terminals with the harness connected won't extinguish the alarm.

This normally open alarm switch idea seems to follow Audi's practice. (I'm not sure that I agree with their practice, but who cares what I think?)

Caveat: I could be wrong.

cnelson14

I ordered and installed a new expansion tank. But the OK sign still flashes the red coolant symbol 30 seconds after start up.

Is there a way to reset the computer, or might it be a problem with the wiring?

Thanks,
Cee Nelson