P059700 error thermostat heater controle circuit: open

[Dasquade]

So in the last 2 weeks i have had this error 3 time now, making my scared and time to investigate closely now.
On mobile atm but if needed i can post the obd11 error later.
Passive error
Engine speed 4200rpms
Coolant temps 73°C
Voltage terminal 13.9v

It throws a mil, but passive error and i can clear it. All 3 times it happend under a mild boost/excaleration...guessing that opens the thermostat.

Coolant levels look okey and no leaks so far i can see, but havent looked specificly at the thermostat itself.
So far i read it is best to check the connector (if i can find and access it?) and look for corrosion. More intense testing involves actual messuring and monitoring voltages i read. Last step if all looks okey os to swap thermostat. Not sure how easy it is too access (i thought easy accessable and located left side near the top front of cilinderhead?).

Any suggestions or experienses would be appreciated. Car has 102.200km and 6y old.

[Dasquade]

Nobody yet had this error before? Taking the car to the garage tomorrow...

[wwhan]

Check here:

01 MIL on (DTC P2181, P0597, or P0599 Cooling system performance)
19 16 71 2038045/3 June 23, 2016.

"S6, S7, RS 7, S8, A8.......2013 - 2015"

"MIL on.
• One or more of the following DTCs is stored in the engine control module (ECM), J623 (address word 01):
• DTC P218100 (Cooling System Performance)
• DTC P059700 (Thermostat heater control circuit open)
• DTC P059900 (Thermostat heater control circuit high)

Technical Background
DTC P218100 will be stored if, after a specified air flow (warm-up phase), the measured engine temperature does not reach the value in the timing map. Particles in the cooling system from the production process affect the closing of the coolant thermostat.

Note: Replacing the coolant temperature sender does not fix the problem."

"Production Solution
Optimized coolant thermostat.

Service
1. Replace the coolant thermostat F265 with part number 079121115BD."

[Dasquade]

Thanks for the info wwhan :)!
Sadely wasn't able to make it to the garage yet, but will go tomorrow.
Can anyone tell me where our thermostat is located? I tried to find it looking down the engine bay but i suppose it is all the way down and just under the crashbar hidden from top view. It is accessable from the underside with panel removed? Hope it doesn't involves removing the front/radiators :s.
(might ask shop to install the CWA pump while they at it and remove air....that is if thermostat is starting to fail and not a wire issue or ECU).

I kept my eye on my FIS gauges and coolant is climbing normal and stays constant once 95-100°C so first look the thermostat is still working (so makes me wonder if it aint an ECU flicker issue as it only gives errors when i push past 4.000rpms). For now i keep it under the 4.000rpm to be safe...

[wwhan]

.....
Can anyone tell me where our thermostat is located? .....

Look in the lower right.

[wwhan]

Also, the thermostat unit has a new Part number: 079121115BL

Supersedes: 079121115BD

You can see the thermostat in this picture. Accessible from underneath?:

[Dasquade]

Okey, so today i went to independant (VAG service) garage. Owner is family and took some time to help pinpoint the issue.
As workservice mentioned, i placed the car on the bridge and firstly checked out the connectors: power connector to the thermostat itself (strangely the grey lockpin was out, but connector was fully inside). Looks brand new and no corrosion but cleaned and sprayed some contact spray in it. Also checked the temperture sensor located slightly above it and that one was perfect aswell. Couldn't reach the waterpomp or connection...

Tested, but still the error popping up everytime i reved it over 4.000rpms. Everything under the 4.000rpm all fine.
Coolant temps all acting normal, same for when i drive. Normal raise of coolant temps and once it reached 80-90 °C the thermostat looks to do its job and keeping the coolant temps under controle (not going past 105°C and dropping when slowing down etc...). No additional errors on the thermostat as you would expect if the thermostat was sticking open or closed or randomly throubleshoot. It is purely under boost past 4.000rpms.
Tested the waterpump, we hear it and it is circulating coolant in the reservoir. Same for the charge cooler pump (not sure if it bypasses or passes the thermostat).

Decided to go to audi garage as second opinion, luckly they were super friendly giving me advice and how things work or what can be done.
They can't check status of the thermostat since it is working with temperture influenced spring that opens and closes by it self. Not much they can test about it, unless replacing the thermostat and see if it is fixed. The sad part is....the entire front needs to come off as like always no room to pull it out from the side/underneat. This offcourse is a labor intense job with no garante it will fixed the behavior.
The latest revision thermostat (BL) works slightly different they told and might need an ECU update....since i have a tune and shop is very far away, not ideally. They said, it isn't a must but they didn't knew what exactly the new update/parameters involved.
Apperently the thermostat is linked to the fuel/air mixture and there a serie of parameters (coolant temps, engine load, air/fuel etc...) that is beeing monitored in combination with the thermostat status. They thinking, especially with the tune, at some moments (under load) my parameters climb outside the target field and triggers the error. But strange since i've been running this tune and setup for a good 2 years now.
The coolant tubes still feel soft when you press on them so system not under overpressure aswell. Offcourse things get hot, not nothing outside what it always been.

So atm i'm a bit stuck tbh and looking for advice. Both garages told me maybe i should wait it out a bit and keep monitoring temps or odd behavior. Normally there are safety feature enough to warm me if engine really is getting too hot etc. Offcourse it consurns me...
*should i wait it out a week or 2 and monitor
*bit the wallet and just go ahead and replace the thermostat (already spoken with the garage i could dismantle the car and partly hire mechanic if needed...stuff like putting car in service mode if you take of the crashbar and stuff, refilling and getting air out system).
*what thermostat, stick with the BD or risk the latest revision without ECU update?

Any advice would be welcome on this specific issue. Sadely not much info to be found especially on the C7 V8.
Personally i do think it is the thermostat and the sort peak boost temps at 4.000rpms offthrows the ecu paramters and causing the error (but still letting the thermostat work?).

On a side note: yeah for some reason my driverside turbo is getting pretty hot and already had to replace the coolant o rings several times (i tried OEM expensive o rings, cheap ones, green (airco) o rings etc....they all fail soon. Not sure if this is a side effect of the heatshielding i did on my hot side of the turbos and manifolds. Exhaust temps are identical for bank 1 and 2 and afaik both turbo's still performing as they should (still got all my boost and torque levels i monitor) and car definatly still feels stage 2 strong, but with there heat issues super scared to go stage 3 or 3+!

[wwhan]

By the way, has the engine coolant ever been changed (G12?)?

From the TSB 2038045/3 June 23, 2016:

"Technical Background
DTC P218100 will be stored if, after a specified air flow (warm-up phase), the measured engine temperature does not reach the value in the timing map. Particles in the cooling system from the production process affect the closing of the coolant thermostat."

[Dasquade]

By the way, has the engine coolant ever been changed (G12?)?

From the TSB 2038045/3 June 23, 2016:

"Technical Background
DTC P218100 will be stored if, after a specified air flow (warm-up phase), the measured engine temperature does not reach the value in the timing map. Particles in the cooling system from the production process affect the closing of the coolant thermostat."

I has been changed, must been 2-3 years ago when we installed my custom cooler (the bigger cooler from the charge cooler system up front). Not sure if they did a full coolant swap or just the cooler and additonally.

But interesting tought and i was moments ago looking into the coolant itself aswell. With the o ring leaks i did had to add coolant a few times (maybe a liter of the 2 years i think...yeah i know, sometimes i delay the o ring swap untill i start to smell it :( ).
I only use premade off the shelf coolant g12 but maybe it would be a good time to swap the entire contence with new fresh coolant (and install my 1 year old CWA100 pump at the same time :s).
Not sure if it is an indication, but when we push the gass and coolant pump overflowed into container, i kinda noticed airbubbles...unless it was created when it gets dumped out the gooze into the container. Been a good half year maybe since i purged the cooler itself (buildin purge bolt on top of cooler) but was fine, no air but directly coolant comming out.

But maybe it helps and maybe it takes out the spikes in the coolant heat when i floor it and stops triggering the hermostat error?
*big thanks for helping thinking wwhan!!
Small change since it isn't throwing the specific P218100 error but a good maintance item non the less. Will check and try :).

[Dasquade]

I might already ask it here :p do we have a proper DIY on the full coolant draining/filling and making it airfree?
Uhu already bought an vacuum/airextruder or how you call it to put on your reservoir to pull it vacuum.
Noticed today on vag service bosh tool (not vcds) that it had a service mode to flush the coolant system (opening and running the coolant pump...pumps?).
I already found on obd11 how i can manually run the main coolant pump, charge cooler pump and the secundairy heat pump (not sure on the term of last one), not sure if any other valves need to be opened. Ideally you need to do this a few times and especially after running it a few times with warm(er) coolant right?