Want to fault find a possible cooling fan issue?
Quite a common fault on TT's
in this section we discuss how to test and fault find your cooling fans, ac and more.
Thermal switch
( may vary model to model) Mounted in the radiator, 3 pin switches than operates based on heat. Controls low and fast speeds, believe to operate at 95 deg & 102 deg. You can unplug the switch and check it by finding the live and then shorting that with the 2 remaining pins separately. Low speed fans should run with Ign OFF, High speed require Ign ON. This will confirm if it is the switch at fault or not.
Coolant Fan control module
( may vary model to model) Mounted underneath the battery, has 2 plugs For the AC they are controlled by the fan control module. With the AC off (Econ On) the fans won’t run until triggered by the thermal switch on the rad. Low speed are switched purely by stage 1 if that switch. High speed are switched by a relay in the fan control module when triggered by stage 2 of the thermal switch.
Coolant temp sensor
( may vary model to model) Located to right hand side of engine, measures the coolant temp twice, once for heater controls and once for dash pods, so these should be within 1-2 degrees of each other. Remember the dash pod is weighted so 80-99 will always sit solidly at 90. If needs replacing always replace seal and always buy genuine. Have seen many aftermarket brands fail. If you have vcds or like you can check measure blocks for coolant temp. ( IF YOU HAVE ACCESS TO A THERMAL CAMERA THAT HELPS TOO )
Fuse box on battery
(middle big one, first green one) Notorious for looking ok but not passing current, visually check, pull the green fuse out and inspect then push back in and make sure seated well. If your car is also only running the fast speed this can also get extremely hot as they are having to work harder than normal.
Large bolt down
– Cooling fans and control module Push in green – cooling fans Cooling fans, 2 speeds, slow speed is resistors ( may vary model to model) Both fans should always run together, there are 2 running speeds, Slow speed is almost silent and unless your standing next to them you probably won’t hear them. High speed is loud, sounds like a turbine starting up haha
The slow speed should always run when a/c is on regardless of temp, if this does not but your a/c is working well its likely your slow speed resistors have failed. In turn if your car is getting to 100 deg on 49c or dash then again same issue.
Fan running when A/C is on
ECON BUTTON- When switched, A/C Compressor is switched off, but operation is otherwise automatic. So, if light on econ is on, you’re a/c is not. You may not have an issue with your fans it could well be an issue with you’re a/c. If you’re a/c is low or excessively filled with refrigerant then it will not work, if you have a leek, if the compressor has failed, a leak in the system or your pressure sensor has failed all these will stop operation of the ac. When turning your climate control on and onto auto you should rear the revs dropped for a second as the ac compressor takes a good current draw.
After run pump
( not 100% relevant but similar subject) ( may vary model to model) It should run for 10 mins each and every time the ignition has been on and turned off. Cools the turbo down to help reduce the risk of heat damage / cracks like these cars are well known for!! That’s what made me swap mine out last year, on a few occasions I could hear the pump not operating. They’re not noisy, but loud enough to hear quite distinctly when standing next to the bonnet. ( only on 225)
