AUDI A3 AVU engine electronic thermostat duty cycle

Hello guyz, i got a problem with an AUDI A3 ...
engine temperature at idle goes up, 100c to 110c, but electronic thermostat doesn't open.
Other shop replaced the thermostat with new OEM.
Fans working at both speeds.
It got many data parameters that i check ...
My focus is on those : when the cooland starts boiling

Engine temp - 111c (that is 231 fahrenheit)
Radiator temp - 48c (that is 118 fahrenheit)
thermostat duty cycle - 0%

i already check the wiring etc ... all looking fine
main power to thermostat from engine main relay - and should PCM controls it by pulse ground (the one is missing)

I know there are many VW - AUDI's guyz around here,
so before i call this "new PCM needed"
i would like if someone knows how much duty cycle (%) that thermostat should be open at idle ??

Thank you for your time

Hey Andreas81! For our info, are you taking measurements with some kind of thermometer at the engine and 'Rad' (ScannerDanner-ese ), or are these data PIDs on the scanner? I'm mostly interested in making sure the ECM is seeing the same readings you are.

I'm not positive what the duty cycle should be, exactly, but I tend to find that heated thermostats generally operate like any other thermostat if there's no heater control. Meaning, they'll open at their specified temperature unless the ECM heats them up sooner. If that's the case on your Audi, then the thermostat should be opening anyway. :huh:

The temperatures you found make me wonder about a coolant flow issue, possibly related to a separated water pump impeller or clogged heater core. We don't get the AVU engine in the US that I know of, but many VW/Audi engines suffered from water pump issues that create low flow and poor cooling. That would mimic a thermostat that doesn't open.

If you're still wondering about the thermostat, then you can try controlling the thermostat yourself with a jumper wire, and see if that improves the engine cooling. If it does, then you can dig deeper into the control problem. If it doesn't, then I'd go in another direction.

An AVU engine would put the car as being a 00 to 03 model year --- that is the exact timeframe when VAG were fitting water pumps with Nylon 66 impellers. The nylon impellers would over time start spinning on the shaft result no coolant circulation.

The electiric part of thermostat is essential there to open the thermostat quicker if the engine is given the beans too soon after a cold start and to shut the coolant flow down more quickly when the throtlle is closed the injectors are cut off

Tyler said it should function like an ordinary thermostat --- but with a hotter opening temperature when the electric pre-heat isn't working.
I would also make 100% sure thermostat fitted is OEM and check the ressistance.

All my temperature readings are correct cuz scanner and laser thermometer are almost the same.

Water pump looks to work ok, at 2000 rpm, up resevoir hose is flew a lot of cooland, also customer said is been replaced.

If as Tyler said that this kind of electronic thermostat should working as mechanical,
is sould be fully open mechanicaly at 110c (230F) ... then why the cooland boiling inside the hoses with cap close ?!!

That kind of engines is trully working that high temp.

Heater core hoses are reading the same temperature, that means cooland flew is free and ok there.

Searching about all that i read how all that stuff works,
There are 2 diff maps inside PCM software
one for cooling the engine at idle and engine running,
and the other when car is moving.

The parameter of wich map PCM will select depents on MAF, Intake air temp, rpm, and both temp sensors, engine load, and fuel

Is there anyway that our PCM would need reprogramming ??
There is no normal explain for that duty cycle to staying at zero when the 2 temp sensors are reading so much big diff temp.

As Tyler suggested is if you provide a ground for the thermostat and the coolant temperature quickly drops you have control problem,
But if the temperature stays high you have a mechanical problem which must either be the thermostat or the radiator. Radiators blocked by congealed coolant are not unknown on German cars

I've seen coolant temp as high as 118 C on an electronic thermostat system on a decel. It's crazy how quick the coolant temp can change in the electronic system. It won't boil because of the radiator cap pressurising the system.

Is there no fault code? If the thermostat is ground side switched, you should be able to go to the control wire at the ecu and see 12v to confirm the circuit. The other way is unplug the thermostat and see if you get a code. Is there no functional test for the thermostat?


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Ok, got some news that make that AUDI even more crazy, haha

I ask customer to bring all the old stuff he replaced as long was searching what's wrong with engine temp.

1st - the old thermostat is 100% burned cuz no resistance at the 2 pins at all and when i plug it in and engine goes at 85c (185F)
DTC coming up - P1292 - so they did correct by replacing it cuz it was stuck ... at least electricaly.

2nd - and even more intresting, is that at a test drive i done, at full engine load, thermostat's duty cycle hit 100% as long car was at WOT.
and temp also when down all times i done that test ...

So that means at least one map inside the PCM is working, and as long temp went down also at the rad,
means that the new T-stat is working also, at least when he gets the comand from the PCM.

Here in Greece very hot these days, so customer told me if i can to remove the mechanical part of the new T-stat, so it will stay cool,
and Climatronic will not stop working, and he will bring it back for further check to find out what's wrong

I will post what i will find when car be back.

P.S there are no DTC stored at PCM - customer's problem from the start was
"some times my A/C is stops after 5 or 10 minutes of driving,
and very rare temp gauge hits 100+ for 10 seconds and then is coming back to normal at middle"

Reading a description of the system the PCM control is OK that is the correct mode of operation

Link to PDF