Hi all!

I bought a used 2.0 TFSI 2016 Q5, that had some minor encounter... Long story short, it needed hood, front bumper and crash reinforcement alongside with whole radiator/fans package being replaced. I bought used radiator package with fans. After installing it on my car, came the time for a first start of an engine and getting rid of all the air in the system... I know, that air bubbles can do strange things to temperature readings. So I made sure there are no more of them (flooding whole cooling stystem took around 11.5 liters, maybe a little bit more). Clue is, that during that process and after it was finished, my radiator fans were dead, not even a single turn on them, despite dash gauge saying 90 degrees on engine and seeing with my own eyes, that water in the coolant tank was boiling... Then I started digging for what can be wrong. Fan fuse, the one next to a kickstart clamping place, was OK, another one in that is in fuse panel B was also OK. Next step was to check what flows where... Connector for temperature sensor next to the radiator has 2.5-2.6Vdc. Next was main connector to the Cooling Fan Control Module. Red wire read some 12Vdc with a change, brown as ground obviously 0. Red/green one (going to smaller pin) also read me 12Vdc with a change and a red/white has 0.26Vdc... All the measurements were taken with only ignition on, car was not started for that. I also unplugged the temp sensor and put a piece of wire into the connector, to simulate it being constantly on, I then started the car, but still radiator fans did not move an inch. I applied 12Vdc directly to the fan motors, and only then they went live. During all the checking AC was not on, as the AC system is not yet filled with gas.

Does anyone with more experience than me see anything that can be at fault? I suspect, that Cooling Fan Control Module I got with radiator/fans package can be at fault, but I am not 100% sure...

 

Do you have a scan tool like VCDS so you can monitor the fan activation duty cycle measuring value, or invoke the fan controller output test? As well as the coolant temp measurement? The radiator fans do not invoke until the coolant temp is 105°C. The coolant temp gauge on the dash is useless for troubleshooting. The coolant system can only be correctly filled via vacuum loading. Did you back the coolant hose off the plenum chamber pipe to expose the bleed hole? Basically, you can make some useful assessment progress if you have VCDS. If not, ....

 

Unfortunately I dont have VCDS... Instead I wanted to force them to work, by cheating with wire put in the coolant temp connector, but even then they still were dead...

 

The EA888 doesn't have a G83 radiator outlet temp sensor. It has only the G62 coolant pump temp sensor.

The J293 fan controller 4 wires are large red 12v supply for motors, large brown ground, small red/green 12v supply for electronics, and small red/white PWM duty cycle control from ECM.

 

Thanks a lot, this post clarified everything for me. But what bugs me is why I have strange value of 0.26V in red/white cable.

 

Because it's PWM. So the ECM is not commanding any significant duty cycle. Though to verify that, you'd have to review the measuring value for fan activation. Don't if you're familiar with PWM on a meter: youtu.be/mMHycv0MPbQ