Coolant Temperature

[touaregv10tdi]

Beetle TDi 2001 Manual Trans ALH
What is the best way to check coolant temp in VCDS ?
I see the temp when I am checking the timing , it says 80C.
I just want to make sure when I am close to hit 94C so I can monitor if my cooling fans are working.
Any tips ?
Thanks

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[DanG144]

Read the temperature in the Engine module, measuring block 7 is good, and read the temperature in Instruments, I do not have the measuring block.
This lets you read both temperature elements in the coolant.

The ECU will start the fans when it sees the temperature is too high, but I do not know the exact setpoint.

The radiator thermo-switch will start the fans when the temperature of the coolant about half way up the radiator is:

Bentley fan operating points:
low speed
on - 197-206 F (92-97 C)
off - 183-195 F (84-91 C)

Fast speed
on - 210-221 F (99-105 C)
off - 195 - 208 (91-98 C)

Which function of your fans are you trying to prove? That they will start from the radiator thermoswitch? or the ECU?
If you are just trying to see if the fans work, I think you already know the easiest way is to turn on your air conditioner.

 

[touaregv10tdi]

If you are just trying to see if the fans work, I think you already know the easiest way is to turn on your air conditioner.

This would be incorrect. When you crank the A/C both fans will indeed come on regardless of the temperature.
Since I have replaced the thermo switch on the bottom of the radiator and the Coolant temp switch , I just want to make sure they will come on when the engine is hot enough.

 

[TDIJetta99]

you just have to let it sit there and run.. it will take quite a while..

The ECU doesn't have any control over the fans on an ALH car... It's done solely by the fan control module and the thermoswitch in the radiator.. The fan control module ONLY turns the fans on with the A/C and has nothing to do with engine temperature, and the thermoswitch turns them on via engine temp.. Low or High depending on temp.. The fans will work via engine temperature even with the fan control module unplugged..

edit.. just seen you have a 2005.. not too sure if the ECU has fan control or not.. I'll look up some wiring diagrams tomorrow

 

[Bob_Fout]

This would be incorrect. When you crank the A/C both fans will indeed come on regardless of the temperature.
Since I have replaced the thermo switch on the bottom of the radiator and the Coolant temp switch , I just want to make sure they will come on when the engine is hot enough.

Dan is correct. If you just want to verify the operational ability of the 2 fans, turn the A/C on. If you want to verify they turn on/off when they are supposed to (sounds like what you're wanting), then you gotta start doing creative things to force the engine to get hot at idle.

 

[Joe_Meehan]

Maybe it would be a good idea to tell us why you want to check the operation? What makes you think there may be a problem?

 

[DanG144]

you just have to let it sit there and run.. it will take quite a while..

The ECU doesn't have any control over the fans on an ALH car... It's done solely by the fan control module and the thermoswitch in the radiator.. The fan control module ONLY turns the fans on with the A/C and has nothing to do with engine temperature, and the thermoswitch turns them on via engine temp.. Low or High depending on temp.. The fans will work via engine temperature even with the fan control module unplugged..

edit.. just seen you have a 2005.. not too sure if the ECU has fan control or not.. I'll look up some wiring diagrams tomorrow

The ECU on ALH cars after May 99 does have some fan control, and the circuitry is the same on the PDs through 2005.5. The BRM is where the shift occurs.

Slow speed fans can be turned on by the radiator thermoswitch - radiator temperature half way down the radiator - no matter if the key is on or off, FCM plugged in or not.
Slow speed fans can also be turned on through the FCM slow speed fan relay when requested by the AC system, or when requested by the ECU.

Fast speed fans are always turned on through the FCM. The request for fast speed fans can come from AC pressure or from the radiator thermoswitch through the FCM, (80% confidence -or from the ECU), but the only relay that turns them on is in the FCM.

I have seen some ALH Engine Control module output tests that do test the slow speed fans, and some that do not. I am not sure why they are different. I never noticed the ALH ECU output fan test until the last year or so - perhaps it is an updated VCDS?

The PD ECU Output tests always checks the ECU's ability to start the slow speed fans. On the BRM it tests the variable speed control.

At least this is my interpretation of the Bentley drawing.

 

[TDIJetta99]

I'll have to look at the diagrams a little more, but there was no wires going to the ECU in any of the ALH diagrams I was looking at.. the only thing I seen where the ECU is involved is the A/C on signal to the ECU, but there were no outputs for the fans at all, unless I just missed them..

 

[JASONP]

You can also do an output test on the cooling fans in the Engine Group 001

 

[TDIJetta99]

You can also do an output test on the cooling fans in the Engine Group 001

on an ALH? all 4 of mine don't do it in the output tests..

I'll try it on the next BRM I get in here..

 

[DanG144]

I'll have to look at the diagrams a little more, but there was no wires going to the ECU in any of the ALH diagrams I was looking at.. the only thing I seen where the ECU is involved is the A/C on signal to the ECU, but there were no outputs for the fans at all, unless I just missed them..

On the schematics the ECU is listed as J...

There are a couple of places where it is shown going to the FCM. The ECU sends signals to the FCM, never to the fans directly.

 

[TDIJetta99]

look a little closer at which wires go to J... they are all inputs, not outputs..

 

[EVO&TDI]

Anyone check their coolant temps on the new 2.0 CR engine? My fan is on half the time after I get off the highway regardless of ambient temperature. On my previous 2 TDIs I never heard the fan kick on even on really hot days and slow driving. I only have a scanguage to go by but on that, my BEW and ALH would both fluctuate from 183-198. In my 2009 JSW it goes from 195-207 and the fan is running quite often. I feel like saying something about it before my warranty is up but maybe it's normal...

 

[DanG144]

look a little closer at which wires go to J... they are all inputs, not outputs..

How can you tell? I have looked pretty close.

I am always willing to learn.

ALL of the A4's can have the ECU override the AC clutch, so that wire has to be dual purpose, right?

And how can some ALH ECU output tests start the fans?

PD's (BEW) have the same schematic, and they ALL have the ECU Output tests start the fans.

It may be time for some functional testing. Unplug the Thermoswitch, turn off the AC and see when/if the ECU starts the fans on high temperature. Not sure how high this will be on my to do list.

 

[DanG144]

Anyone check their coolant temps on the new 2.0 CR engine? My fan is on half the time after I get off the highway regardless of ambient temperature. On my previous 2 TDIs I never heard the fan kick on even on really hot days and slow driving. I only have a scanguage to go by but on that, my BEW and ALH would both fluctuate from 183-198. In my 2009 JSW it goes from 195-207 and the fan is running quite often. I feel like saying something about it before my warranty is up but maybe it's normal...

I have never noticed my fans operating on the 2010. Though they must be running with the AC on.

You do know about the regen of the DPF? If that is in progress when the car is turned off the fan will run for about 10 minutes after shutdown.

It surely will not hurt to mention the symptoms.

That temperature range is very close to normal. Though I do not know what mine runs at. My 2005 runs from 193 to 204. The fans never run on it due to temperature.

 

[TDIJetta99]

How can you tell? I have looked pretty close.

I am always willing to learn.

ALL of the A4's can have the ECU override the AC clutch, so that wire has to be dual purpose, right?

And how can some ALH ECU output tests start the fans?

PD's (BEW) have the same schematic, and they ALL have the ECU Output tests start the fans.

It may be time for some functional testing. Unplug the Thermoswitch, turn off the AC and see when/if the ECU starts the fans on high temperature. Not sure how high this will be on my to do list.

If the wire is coming from a sensor, then it's an input, like the one coming from the A/C pressure sensor/switch.. The other 2 are from the fan controller, one is the signal wire that the ECU uses to tell when the a/c is ON, the other is the one for the compressor interrupt..

Actually looking at the diagram a little closer it appears that the fan control module interrupts the compressor using the input from G65 (high pressure sensor), and the ECU just monitors that circuit.. I'll have to mess with one of them tomorrow.. Now I'm really curious..