Cooling Fan Running Continuously

[SwaitsySG]

Hi all. 

Apologies if this has been covered before. Still chasing a cooling fan problem on my 2.0TDI Avant. Recently went for an MOT.  The fan unit was completely dead so not kicking in during the emissions test.

I've replaced the fan unit and control module. The new fan comes on full tilt when the car starts up and now runs continuously until you switch the engine off.

 

Any advice is appreciated. A relay issue maybe? Sensor? I should add this is the single fan unit.

 

Cheers all.

[Steve Q]

I'd recommend a diagnostic check before you start changing sensors. It could be a sensor. Does the engine heat up etc as it should. 

[SwaitsySG]

Hi Steve. I've an nt680 scanner. No faults found. Engine heats up to operating temperature and otherwise behaves as normal.

I've tried testing continuity, got 0.6 ohms between the connector in the plenum box and the fan plug, matching the default on the meter.  

[Steve Q]

Could it be an issue with the dpf I wonder? The car thinking it needs to keep the fan on during a regeneration 

[SwaitsySG]

Could be a reason. That would mean forcing a regen though. Not something I can do.

[Steve Q]

5 hours ago, SwaitsySG said:

Could be a reason. That would mean forcing a regen though. Not something I can do.

The only thing that goes against my dpf theory is that you'd think there'd be a fault code. 

[SwaitsySG]

It's one thing going against a lot of the sensor theories; there's no fault codes. The last one was with the old fan. 😩 I'm told the relay is actually in the fan motor itself, ss opposed to a seperate one that can be pulled and replaced. 

I'm honestly stumped. Unless the fan I've put in is faulty, despite it spinning when the car is started.

[Magnet]

Hello Chris,

Its probably me, but I think a recap might help here, and this is my stab at it:- ( some is assumption, and all open to correction)

Coolant always had,and still does, heat up sensibly to normal temperature. 
Your fan always remained off (as it generally should do) and you had no reason to suspect an issue, until the fan didn’t come on during an MOT test - as you believe it should have -? 
It now stay on continuously following you renewing components. 

You have now renewed the fan unit, and it’s control module, and it now stays on continuously -? Did you change both items at the same time -?  If so, this is not my convention of ‘change one thing at a time and test’. 
Worth replacing one of the two items at a time with the old units -? 
Is there a coolant temperature sensor on the radiator which senses an over-heat and then activates the fan? If so, is this at fault and remains closed-curcuit even when it shouldn’t be? 
Anyway, I digress when I’m not really sure about the history of the issue.

Can you do us a kindness Chris, and re-post this on a timeline basis, also clarifying what I’ve written/question. 
Kind regards,

Gareth. 

 

[SwaitsySG]

Aye, so it went like this;

The old fan didn't work. The chap at the garage was reluctant to complete the emissions test on this basis, as it wasn't kicking in when holding the engine at higher end revs. When the car is out on the road the temp gauge sits where it's supposed to and the car runs quite happily. Its never overheated. But static in a garage, held at high revs for the emissions test, he was concerned that the engine might get too hot as the fan wouldn't kick in, so the test wasn't completed.

My OBD scanner brought up a low control circuit fault and a blocked/difficulty of movement fault. There was no physical obstruction to the fan but the module terminals were quite corroded. Admittedly I only tested continuity of the power cable from the plenum chamber to the fan plug. That was fine and corrosion free.

I sourced a replacement unit from an Audi motor factor as it was inexpensive, included both the fan and module, and tested and deemed to be 'in working order'. It could well be that this is at fault but I took a punt, two birds with one stone and aw that. I'd thought maybe a relay was the problem but was told it's in the fan motor itself on this particular setup. (CAGB 2009 2.0TDI with single fan).

Installing the replacement fan and module, the 'new' fan comes on about 10 seconds after the engine is started And stays on until a couple seconds after the engine is switched off.

There's no fault codes showing for the replacement fan. In fact, there's no fault codes coming up at all. Not for the fan, or any sensors. No lights on the dash either, such as for a dpf regen.

There's two temp sensors on this engine, both on the back I believe. The main one is easy enough to reach though a mirror is required as there's no direct line of sight when changing it. That may be worth testing, or even changing as it's a quick job and costs buttons. But again, no fault codes relating to that.

The sensor on the rad, which has also been known to contribute to misbehaving fans is the AC pressure sensor. Again no fault codes.  

That brings me to where i am at the moment, if that builds a better picture.

[Magnet]

Thanks Chris. So now we have a more complete story, but apologies some ‘history’ questions remain:- 

It seems you knew (how?) that the fan wasn’t cutting (as it shouldn’t do unless overheated?), but had it ever overheated or caused you problems before you presented it for an MOT? So in effect, were you happy with the car at this point? 
The MOT tester refused to carryout the test because the fan didn’t cut in - odd. Hopefully we may get some MOT experienced testers on here to clarify, but I’ve never experienced this, and invariably the ‘oil temperature by-passed’ is normally recorded. 
‘Held at high revs’ for emissions ..’ surely it’s 2,500rpm-? Not high, and on a timed 2? minutes, so where is the concern-? Just wonder if there was any history with this tester and subsequent engine problems -? 
Has the car subsequently been MOT’d by another garage? 
Anyway, moving forward:- 

You say you bought both parts from ‘an Audi motorfactors’ and they were cheap. Do you mean a Audi specialists such as TPS, or just an ordinary motorfactors who sell parts for Audi and all other marques? Were the parts a recognised make? 
As I’ve said Chris, for a start, I would replace each original part in turn and see where you get. 
Re. AC association of continuously running fan. Not certain on your model if fan ( or one of them) might continuously run if AC is on, so possibility -? Re. AC issues - there was a lot of posts about pressure sensors and their effect on AC problems, so might be worth a look up. 
Keep on the good work. 
Kind regards,

Gareth. 

[SwaitsySG]

Thanks for the reply Gareth. So basically while doing the emissions test the temp gauge started to creep up during the test. Technically 'overheating' in so far as it crept above normal operating temp, high enough that the fan should have kicked in but didn't, but not high enough to be catastrophic. Not into the red. So the test was abandoned, the tester airing on the side of caution. Under normal driving conditions the temp has never gone above normal operating temp. Gauge has always been rock solid. Sorry, I should have made that clearer. With the replacement fan technically working, albeit on the full time the engine is running, the car is going back to the same chap to complete the emissions test. 

And yes, 2500 revs. Or at least I assume he was running it stationary at 2500. I was unintentionally vague there. When I said higher revs I didn't mean top end. I forget that the revs generally only ever reach 2500 for a second or two at a time while changing up through the lower gears. Usually i change gear slightly before that anyway. Normal daily driving it never sits that high consistently. 70mph in 6th on the motorway you're looking at 1900rpm. 

Cheap is a misinterpreted word in this context. Inexpensive would have been better. Prestige Motor Services. (Dunno how good or bad their rep is within the Audi community. If any). They describe themselves as specialist Audi breakers, to use their words, that deal mainly in new and used Audi parts. I'll admit used electrical part - a gamble. Fair enough. 

With your advice in mind, I won't be getting any more parts until I've done more testing on what's already there so I'll look into AC pressure sensors following that. I'll add at this point that the fan will run continuously regardless of whether the AC is switched on or off. The AC needs recharged but if its switched off I'd have thought that wouldn't affect the fan. Its the single fan unit. So a main rad fan on one side and louvres on the other.

[Stevey Y]

1 hour ago, Magnet said:

Thanks Chris. So now we have a more complete story, but apologies some ‘history’ questions remain:- 

It seems you knew (how?) that the fan wasn’t cutting (as it shouldn’t do unless overheated?), but had it ever overheated or caused you problems before you presented it for an MOT? So in effect, were you happy with the car at this point? 
The MOT tester refused to carryout the test because the fan didn’t cut in - odd. Hopefully we may get some MOT experienced testers on here to clarify, but I’ve never experienced this, and invariably the ‘oil temperature by-passed’ is normally recorded. 
‘Held at high revs’ for emissions ..’ surely it’s 2,500rpm-? Not high, and on a timed 2? minutes, so where is the concern-? Just wonder if there was any history with this tester and subsequent engine problems -? 
Has the car subsequently been MOT’d by another garage? 
Anyway, moving forward:- 

You say you bought both parts from ‘an Audi motorfactors’ and they were cheap. Do you mean a Audi specialists such as TPS, or just an ordinary motorfactors who sell parts for Audi and all other marques? Were the parts a recognised make? 
As I’ve said Chris, for a start, I would replace each original part in turn and see where you get. 
Re. AC association of continuously running fan. Not certain on your model if fan ( or one of them) might continuously run if AC is on, so possibility -? Re. AC issues - there was a lot of posts about pressure sensors and their effect on AC problems, so might be worth a look up. 
Keep on the good work. 
Kind regards,

Gareth. 

Hi Gareth if you read the first post it mentions its a single fan system, the easiest way to test the old system would have been to switch the aircon on and if its the fan gone it won't work, as for the fan coming on for the emissions test the tester must have worn his pants on his head and taught the wrong end to talk, has anyone checked the flow rate on these radiators its phenomenal, the total thesis behind emission reduction is cooler running this equates to bigger radiators, I have only had my fan come on naturally once since I have had my car  and that was on the forty degree Tuesday we had this year and I was stuck in stop start traffic for ten miles on the M25 even then it was only on for about three min, when I had my cam belt changed they left it running for best part of an hour with no expansion tank cap on to get rid of any air and the fan never once kicked I can attest to that as I was standing right by it adding antifreeze as required.

Steve. 

[Stevey Y]

16 minutes ago, SwaitsySG said:

Thanks for the reply Gareth. So basically while doing the emissions test the temp gauge started to creep up during the test. Technically 'overheating' in so far as it crept above normal operating temp, high enough that the fan should have kicked in but didn't, but not high enough to be catastrophic. Not into the red. So the test was abandoned, the tester airing on the side of caution. Under normal driving conditions the temp has never gone above normal operating temp. Gauge has always been rock solid. Sorry, I should have made that clearer. With the replacement fan technically working, albeit on the full time the engine is running, the car is going back to the same chap to complete the its own separate sensore emissions test. 

And yes, 2500 revs. Or at least I assume he was running it stationary at 2500. I was unintentionally vague there. When I said higher revs I didn't mean top end. I forget that the revs generally only ever reach 2500 for a second or two at a time while changing up through the lower gears. Usually i change gear slightly before that anyway. Normal daily driving it never sits that high consistently. 70mph in 6th on the motorway you're looking at 1900rpm. 

Cheap is a misinterpreted word in this context. Inexpensive would have been better. Prestige Motor Services. (Dunno how good or bad their rep is within the Audi community. If any). They describe themselves as specialist Audi breakers, to use their words, that deal mainly in new and used Audi parts. I'll admit used electrical part - a gamble. Fair enough. 

With your advice in mind, I won't be getting any more parts until I've done more testing on what's already there so I'll look into AC pressure sensors following that. I'll add at this point that the fan will run continuously regardless of whether the AC is switched on or off. The AC needs recharged but if its switched off I'd have thought that would affect the fan. Its the single fan unit. So a main rad fan on one side and louvres on the other.

Hi its quite possibly a water temperature sensor as they don't affect the gauge which has its own separate sensor.

 

Steve.

[Magnet]

Oops, sorry then Steve- single fan. 

Yes, got a bit of a job to induce the fan to come on these days, that’s why I find it confusing that Chris said he ‘knew it wasn’t working’ before MOT, and my question how he knew. 

[SwaitsySG]

I'll need to look into the water temp sensor theory Stevey, cheers for the suggestion. I agree with what you're saying about the coolant flow rate. Mine has sat quite happily idling in traffic on hot days without problem. I've never had an overheating issue with that car. Though I can't say I've ever held the revs at 2500+ for extended periods of time. 

As far as the emissions test goes I dunno. That's just what the man said. Needless to say the mot has now been done and the car has passed. 

Regarding the AC as i say, the old fan did nothing when I switched it on but as mentioned the system needs recharged. I don't know whether that affects matters, but certainly from an electrical standpoint switching it on did hee haw. As far as 'knowing' the fan was goosed, I didn't. I just figured it was, between the faults and the lack of any sort of life.

Never had an A6 before now but the fan used to kick in on my 2017 Leon ST quite frequently. Wasn't unusual to hear it whirring away as I parked up after decent run. Newer car and a later gen 2.0TDI though so maybe not a fair comparison. 

[Stevey Y]

21 hours ago, SwaitsySG said:

I'll need to look into the water temp sensor theory Stevey, cheers for the suggestion. I agree with what you're saying about the coolant flow rate. Mine has sat quite happily idling in traffic on hot days without problem. I've never had an overheating issue with that car. Though I can't say I've ever held the revs at 2500+ for extended periods of time. 

As far as the emissions test goes I dunno. That's just what the man said. Needless to say the mot has now been done and the car has passed. 

Regarding the AC as i say, the old fan did nothing when I switched it on but as mentioned the system needs recharged. I don't know whether that affects matters, but certainly from an electrical standpoint switching it on did hee haw. As far as 'knowing' the fan was goosed, I didn't. I just figured it was, between the faults and the lack of any sort of life.

Never had an A6 before now but the fan used to kick in on my 2017 Leon ST quite frequently. Wasn't unusual to hear it whirring away as I parked up after decent run. Newer car and a later gen 2.0TDI though so maybe not a fair comparison. 

Hi the lack of refrigerant may well affect the operation of the fan as the A/C unit senses no gas pressure, and being a single fan system the fan won't operate, with regard to the LEON they use the same radiator as the Skodas and this summer all the Octavias on our cab circuit had the fans going 24/7, small rads and a transverse engine no real natural airflow over the hot bits like you get with the north south configurations on our engines, if you held the revs at 2500 for the two mins required and the car overheated you wold have a real problem , head gasket/thermostat.

Steve.