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I have a problem with the coolant level sensor. After a minute of driving the temperature sensor on the car starts flashing and also alerts with beeping.

Of course the coolant tank level is normal.

The temperature shows 120°C for a few seconds, than it returns back to normal (60-70). As the car is being started for only few moments (max. a minute), this is weird..

Following this thread didn't help neither.

I've already bought a new temperature sensor, because it was the first suspect for this issue. But without success.

Is there something that I've forgotten? Any suggestions/advices?

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  • You said you bought a new temperature sensor, yet you originally ask about the coolant level sensor. Are there two issues going on, or is there one sensor doing two jobs? Also, have you checked for air in the system? After it goes to 120°C, then back to normal, does it stay at the normal state, or does it go back up to the high temp mark at any point afterwards? – Pᴀᴜʟsᴛᴇʀ2♦ Jun 15 '15 at 11:02
  • As I know, this is the same thing (coolant /temp. sensor). I didn't check for the air yet. Yes, it stays in the normal state back. But sometimes it happens that it stays at 120°C all the time while driving. – balex Jun 15 '15 at 12:01
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My research shows that there isn't a coolant level sensor (though my research could be flawed) in the A4 1.6L vehicle. It just has a temperature sensor. While this could be your issue, you should change out this sensor since you've already purchased it anyway (it seems the part itself is not that expensive anyway). You'll also want to check to see if there are any air pockets in your coolant system. This, too, can cause issues with errant readings like you are suggesting.

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It could be a sensor or wiring fault. The sensor in question is located on the plastic "ball" thing where you fill the coolant up.

Make sure it doesn't have too much coolant in the ball thing too as it's really easy to air-lock them.

Our '97 1.6 Golf does the exact same thing if the coolant level is even slightly low. The other thing to check is that your heater matrix isn't leaking internally as this could cause air bubbles.

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Assuming that Audis have more than a passing similarity to their VW relatives, there will be a coolant level sensor in the coolant reservoir "ball." The sensor is a pair of probes that look to be made of stainless steel that come down into a small coolant dam in the tank. You can easily see if they are there by looking down from the top when the tank is open.

If they are there it would be worth cleaning them with a bit of ScotchBrite or something similar. They sense the presence of coolant by detecting (or maybe even measuring) conductivity between the two probes. If they become contaminated they can fail to work.

So, if the coolant level looks good, I'd start by cleaning them. It's quicker and less expensive than replacing them (which I think means replacing the coolant reservoir).

The temperature glitches suggest a few things to me:

  1. Damaged wiring between the sensor and the gauge, or
  2. Maybe air in the cooling system – I'm not sure exactly what to expect but if there was air trapped in the system and it caused the temperature sensor to loose contact with the coolant it seems that you could see the reading jump one way or the other. What I'm not sure about is if the pressure in the cooling system is high enough for the temperature to get all the way up to 120º C.
  3. A failing sensor.

Since you've swapped the sensor it seems that one of the first two is the most likely explanation. I suppose it would also be possible for air trapped in the cooling system to cause enough disruption in normal liquid levels that it might cause the coolant level sensor to give you false alarms.

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