I have had problems for the last 9 months in my A4 B5 2.4 with the temp not getting up high enough.
I always figured it was a stuck thermostat..… and you know what work is involved in fixing a $19 thermostat...

Now, after finding out that in the climate control codes that (51) is the actual water temp, I try it and find the car stays at a constant 90°c when driving

Its the tempature sender unit to the dashboard indicator that's broken after all that.
Now that's probably a $20 item that can be replaced in a hour.

(9 months.…9 months....!)

Thankyou sooo much for this info.

 

I have a Audi a4 v6 1996, I want to no how can I reset my cooling system if I drive not Evan 1km then the car over heat, I just want to no how to reset my settings please.

 

First, if it's overheating, is it just the dashboard temp or a actual overheating where the coolant gets too hot?
If the coolants getting too hot & it's overheating very quickly, my guess is with the thermostat is stuck closed, or it's a bad waterpump.
My first guess if it's only taking a minute to overheat is that the waterpump shaft has broken inside the unit & the pump fin part is not even turning around.
If it was taking several minutes to overheat, I would be expecting that the plastic fins on the waterpump have disintergrated.
If it was taking a bit longer, then I would say it's the thermostat that's stuck closed.
Even longer to overheat, then maybe the switch near the bottom of the radiator that controls the fans, has broken.

To check if the waterpump fins have disintergrated, drain some coolant out via a bottom of the radiator hose & check it for tiny black plasticy flakes. I guess you could burn some of that residue on Aluminium foil to see what it does, to see if it gives off plastic fumes when burnt.

I have another A4B5 2.4 which has done this, it takes about Ten minutes to overheat. There's thin black flakes in the coolant.
So I have bought new waterpumps, thermostats, timing belt & crankshaft locking pin so I can do both of my 2.4 engines at the same time.
I am now sure that my A4B5 that I mentioned above, years ago, has a stuck open thermostat, since then it overheated & split the plastic thermostat housing, so I bought the Aluminium version to replace it as well.
Since then I have figured out that the dashboard temp sensor unit is in the glow of the coolant that circulates around the year of the engine & flows thru the Heater core ( to get heat into the car itself quickly ).
I was mislead by the fact that the heater box unit flaps were leaking air thru the flaps, which makes the ',hot air' comming from the heater turn cold.
There's lots of stuff to learn on these cars, once you know, it's easy.

So, check your radiator hoses for heat, if they are cold, the waterpump is not pumping coolant thru them. Then check the coolant for the black plastic residue from the waterpump.

Your heater will probably not be working properly because of the holes in the heater flaps, Google/search for this, it's a big job to fix it.
I have fixed one car so far & am stuck 1/2 way thru fixing my second A4B5. Now I still have to fix the 2x 2.4 V6 versions that I have.
The big clue here is that you will find small flakes of greenish grey foam stuck behind the dashboard vents, or bits flying out of it when you turn the air on.

Good luck. What's the coolant condition like? My theory is that if the coolants not changed when it's supposed to be, it degrades the waterpump fins.

Parts are really cheap & once you have watched 3 or 4 different YouTube videos of the Timing belt/ Waterpump / Thermostat job being done, you get a LOT more confident about doing the job.
Get the Aluminium version Thermostat housing to replace the plastic one if that's what your car has. It's easy to check by peeling part of the radiator hose that's clamped onto it, back, to see if it's Ali or Plastic.

 

A shot in the dark, I wonder if anyone sees this..
I'm having trouble with the ECT warning light coming on in my a6 c4. All the gauges and the Channel 51 on my climate control shows the correct temperature, and coolant flows throught the system and doesn't overheat. Channel 26 on the other hand shows 002-004. Where does it get it's information from? I assume it's supposed to show resistance numbers, and this low number means some sensor doesn't work properly, but I've exchanged a couple with no luck and even two local repair shops couldn't find a source for the problem. The AC compressor doesn't switch on when the warning light is on, so it's a major nuisance in addition to the ever blinking light in the dark, even though there's no overheating problem.

 

I want to no how can I reset my cooling system if I drive not Evan 1km then the car over heat, I just want to no how to reset my settings please.