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Coolant fans constantly running

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Jimt5 View Drop Down
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    Posted: 05 Nov 18 at 11:22
Ok so I have an 05 130 6 speed no ac. Fans were running when I got it, too date I have replaced head temp sensor, rad sensor air sensor and control unit, all genuine parts except the sensor in the rad. Fan is still on, when I put it on vag com it says g62 signal to high. If I reset I can hear the fan speed temporarily slow and then back on full.
Any plugs I have looked at look ok with no obvious sign of corrosion. I've had the front off to do manifold gaskets and power steering pump and the wiring from what I can see looks ok, I haven't peeled back any insulation on it but I have popped what I can out of the trunking it's carried in. Also when I pull the brown fan plug from the control unit the fans go off and the temp gauge works perfectly, goes slowly up to 90 and stays there. I have checked fuses in centre console and under the battery. Starting to get annoyed with it now as I'm sure it's something simple. HELP
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Post Options Post Options   Thanks (0) Thanks(0)   Quote T5 TDI Quote  Post ReplyReply Direct Link To This Post Posted: 05 Nov 18 at 17:01
When you say the 'head temp sensor' the only one I know of on your 5 cyl is in the block and that is the the G62 mentioned in your code.  It is at the front of the engine below the oil cooler.  If you didn't have to take the pull the front back and then still spend a long time cursing you haven't changed it!  It can certainly cause the fan to stay on.  If you still have access to VCDS you can see what the G62 is reporting live by opening the engine controller then going to 'Measuring Blocks'.



Edited by T5 TDI - 05 Nov 18 at 17:48
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jimt5 Quote  Post ReplyReply Direct Link To This Post Posted: 05 Nov 18 at 17:57
Yep the g62 I replaced as well as the others and the control unit. It shows as "signal to high" on vag com.
I don't understand how it shows faulty with a new one yet it appears to communicate ok with the temperature gauge. Also I'm not sure how long is too long but the glow plugs seem to operate quite a long time, possibly 5 seconds. That said for 240 kms it does start well hot and cold.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote T5 TDI Quote  Post ReplyReply Direct Link To This Post Posted: 05 Nov 18 at 23:37
Originally posted by Jimt5 Jimt5 wrote:

Yep the g62 I replaced as well as the others and the control unit. It shows as "signal to high" on vag com.
I don't understand how it shows faulty with a new one yet it appears to communicate ok with the temperature gauge. Also I'm not sure how long is too long but the glow plugs seem to operate quite a long time, possibly 5 seconds. That said for 240 kms it does start well hot and cold.

You should post up your own take on replacing that sensor.  Thumbs Up  Any new tips are welcome here.  The 2.5 is such a different beast from your run of the mill 1.9 Wink   It's surprising how little detail about the more difficult bits of the 2.5 exists on the web.  

Is the G62 reporting sensibly live on your VCDS?  I don't know how it is with hookey versions of VCDS but with mine I could start up from cold, connect VCDS and log the coolant sensor live on a hilly drive.  On the screen I would expect to see the G62 sensor reporting the coolant temp in real time.  The resulting list of figures (log) should start with roughly ambient temperature and show a steady increase according to your type of drive.  I'm surprised that you have that fault code if the G62 is showing normal live data via diagnostics.  

Re the glow plugs- 5 seconds is a bit long for any TDI engine but no big deal.  Mine does that but only at about -5c or less.  It will probably fix itself when you get to the bottom of your fault.  I was just going to ask if you had fitted a genuine sensor but I don't think there is anything else (hence the £50!)

Re the fact that your temp gauge is working ok- My gauge was dropping out occasionally but the fans were misbehaving differently so maybe it depends on exactly how the G62 fails internally.  Unlike older VW's, there are no separate sensors for ECU and gauge.  An ECU fault could cause your problems but I would definitely start with the live data and then look at the loom from the G62 sensor to the ECU. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Stryne Quote  Post ReplyReply Direct Link To This Post Posted: 06 Nov 18 at 02:28
What about the ambient sensor behind the bumper cover, won't the fans keep going if it is disconnected ?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jimt5 Quote  Post ReplyReply Direct Link To This Post Posted: 06 Nov 18 at 07:41
Yes they will keep running. I fitted a new one.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jimt5 Quote  Post ReplyReply Direct Link To This Post Posted: 06 Nov 18 at 07:42
Ever hear about a faulty new G62 ?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote T5 TDI Quote  Post ReplyReply Direct Link To This Post Posted: 06 Nov 18 at 09:14
Not a genuine G62 but it is possible. That's why it's worth checking the live data from it.  You could re-check the connector to it to make sure none of the pins got bent as it got plugged back in.  Because of the pigtail on the loom you should just about be able to get at it.  

Another possibility (if the sensor didn't come in a sealed polythene pack which they should have) is the the loom got tweaked by someone using it to pull the sensor out with, this is if someone else has fitted it before you and then returned it as not wanted.  (VW won't usually except electrical stuff back though). 

Did you check the fuses with a test lamp or meter?  I say this because the small rated engine management fuses can easily be blown yet still look perfect.  Any sensor that reports a signal to the ECU that makes the ECU think it may not have full control of the cooling system will put the fans on as a precaution, and any faulty wiring that causes the ECU to get an incorrect signal could do the same.  So could a faulty ECU but not so common on T5's.

If you can find out what resistances you should be seeing on the sensor pins at various temps you could check the sensor but VCDS will do that more easily.  

You should check all earths, I think there is one on the fan controller itself and another on the top starter bolt.  Actually take them off and clean them up really well. 


Edited by T5 TDI - 06 Nov 18 at 09:18
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Post Options Post Options   Thanks (0) Thanks(0)   Quote T5 TDI Quote  Post ReplyReply Direct Link To This Post Posted: 06 Nov 18 at 09:21
Originally posted by Stryne Stryne wrote:

What about the ambient sensor behind the bumper cover, won't the fans keep going if it is disconnected ?

It will as mentioned but it will also leave a fault code identifying it.  Jim only has the G62 code.


Edited by T5 TDI - 06 Nov 18 at 09:22
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jimt5 Quote  Post ReplyReply Direct Link To This Post Posted: 06 Nov 18 at 09:42
Fuse locations seem to be a closely guarded secret, even my Haynes manual doesn't go into great detail. Are there any important ones under the battery?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Stryne Quote  Post ReplyReply Direct Link To This Post Posted: 06 Nov 18 at 12:33
Fuse SA 7, Power to Fan controller (60 A or 70 A equip dep) under battery, or Fuse SA 8 some models.

Fuse SD1 (Fuse no. 1 - 5A) to Rad fan control unit, fuse holder near headlight ahead of battery

There are 2 earth connections at the control unit shown in the wiring 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jimt5 Quote  Post ReplyReply Direct Link To This Post Posted: 06 Nov 18 at 12:43
I have been rooting around at fuses under there. However from what I read sometimes the small fuses can be blown and still look intact, I'll check them all individually.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote T5 TDI Quote  Post ReplyReply Direct Link To This Post Posted: 06 Nov 18 at 13:23
Check them with ignition on but don't pull them out otherwise you might create codes you will need to clear.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jimt5 Quote  Post ReplyReply Direct Link To This Post Posted: 06 Nov 18 at 13:57
I'll give that a go later. Strangely I know a guy with a 06 auto and he has had the same issues. He ended up installing an on off switch on the dash, I however have spent a few quid and a lot of time on this and am getting stubborn about fixing it the right way. That said has anyone rigged up a simple switch thermostat switch ? Could one be rigged up with the existing radiator switch I wonder?
What would concern me is with the existing fault and the fact that the glow plug light illuminates for a reasonably long time are other systems being thrown out especially fueling.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Stryne Quote  Post ReplyReply Direct Link To This Post Posted: 07 Nov 18 at 12:42
Seeing that others have had engine wiring faults like breaks, chafing, faulty connectors, I'd suggest carefully inspecting that engine wiring from 
the sensor area across to the E Box area under the battery. That's probably obvious to you, but can't think of much else atm.
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