Please help, folks

Car - 2005 1Z5 combi 1.9tdi PD 8 valve. I have had this car since 2008 and now it has covered just shy of 300,000 miles. The car is in really good condition, well serviced but now it doesn't have much value.

Recently, I noticed that instead of taking its time to get up to temperature, t has been quickly getting up to normal but not overheating, so everything fine....

Then I noticed that the air con wasn't working......... So, I thought about this and then had a look at both of the fans behind the radiator.

Lo and behold neither fan was working, dead as dead can be. I did my research and the most likely suspect seems to be the Fan controller unit situated behind the main engine cooling fan.

Of course it could be that there in no electricity getting to the main plug(bottom left corner of the radiator).

My ability with car electrics is very limited and for some reason I find the wiring on the skoda to be needlessly complicated.

I have removed the cooling fan unit complete (quite easy), removed the controller unit and applied 12volts to both fans and they both work so, logically this leaves me with a faulty controller unit and/or a failed power supply. I have looked at the fuses in the engine bay (f/n/s against the battery) and they all seem to be fine.

My thinking is that the controller unit has failed as I have already had to replace it once before but of course I am not sure as I find it difficult to test the electrical supply as I don't know which wires are supposed to be live and which are not.

I have attached the photo i have taken of the connector and wiring.

So advice would be greatly appreciated. I am tempted to go ahead and get another controller unit but I am not sure that the controller is the problem. The las replacement was a long time agao now but not that long. It is an NRF controller

Thanks to all if you got this far. I will watch out for replies

Thx again

Tom

Thick brown is earth.

Thick red is permanent 12V.

Blue/red will be a switched 12V, only there when engine on.

Other wire will be control signal from engine ECU.

Pete,

You again......loool!! You always respond to my posts, I am v grateful (You may not remember but you gave great help with another wiring problem some time back (now successfully repaired thanks to your advice.)

I hardly ever post as my car is so reliable. I really do appreciate your response.

So, the thick red is permanent live as in ignition off, key out?

In that case is it ok for me to test the supply with a simple screwdriver type circuit tester?

Red across to brown and blue/red to brown with ignition on or engine running?

Regards

Tom

Edited 25 July25 Jul by ThomasP

29 minutes ago, ThomasP said:

So, the thick red is permanent live as in ignition off, key out?

Yep

Test with whatever you have available

🙂

Pete

thx again

My kit is so basic that I've just ordered a screwdriver type tester....lol.

I'll deffo get back to you

Thx

Tom

Pete (and any other person interested)

I found an old chinesium multitester and have now tested the electrical connector as advised above and I do have battery voltage across red and brown (everything off) and I have battery voltage across blue/red with ignition on.

Therefore, I have proved the electrical power is present.

The connector itself appears to be in v good condition with no corrosion visible so unless it is the ecu control wire which i doubt (if it is the ecu/wiring from the ecu the car won't be worth repairing, (i think).

Therefore, it seems to me that the controller is the only thing that can be faulty (both fans run when they receive 12 volts).

As I said above the controller is an NRF make and it hasn't really lasted that long before failure Perhaps 2 years.

There are loads of these controllers available from £60 odd all the way down to £22. I suspect they will all be chinese copies. Or should i buy a whole cooling unit?

Can anyone advise on a good make (not a Skoda dealer)?

Pete, I hope you read this post. I will watch for any replies.

Tom

On 26/07/2026 at 19:59, ThomasP said:

Or should i buy a whole cooling unit?

I wouldn't if the fans work and aren't noisy (bearing noise).

On 26/07/2026 at 19:59, ThomasP said:

£60 odd all the way down to £22.

Mid range maybe ok, or look at a more reputable brand on Skoda part net

BlueWagon

Thanks for the response...... I thought so too. There's always that old adage...'If it's not broken, don't fix it'.

I've ordered one controller for £32 odd on ebay.......

I will fit it when it arrives and report back.

Thx again, BlueWagon for your response.

Regards

Tom

UPDATE

Disappointment, I'm afraid.

My brand new controller unit duly arrived and I've now fitted it but the problem remains the same.

I have previously tested the wires (apart from the command wire from the ecu) and proved that the relevant power was correct at the different wires.

The only wire I have not tested (and don't know how to) is the command wire which seems to me to be the only connection that can now be faulty (unless there is some sneaky fuse hidden away somewhere).

Both fans do not rotate at all. The car quickly gets up to temperature and remains steadfastly on 90 degrees but of course I haven't been stuck in any traffic jams. Air con does not work and the fan (the smaller one) doesn't operate with the engine on and air con switched on.

There is no engine management light on either.

If any one can offer a solution I would be grateful........ perhaps identifying the command wire as it comes out of the ecu then I can test for continuity at the fan connector..

Car:- 1Z5 combi 2005 BKC 1.9tdi withe just short of 300,000 miles on it

All help appreciated, thx.

Regards

Tom

Stupid question but have you checked for fault codes? If one is present the ECU often shuts down that particular function t avoid further damage. It may be that the controller was faulty and has been shutdown but that code is still present and hence the new one won't function either?

Skomaz

thanks v much for a very interesting response and no it's not a stupid question. I don't really have the kit to check what you mention. I just have a v v basic chinesium obd2 reader (basically i bought it to get rid of pesky eml lights).

Tom

UPDATE

I'm afraid I'm still having no success. I have researched quite a lot but still am unsure what the problem is.....

The cooling fan module has now been replaced with absolutely no change.

So, the position is that the fans do not rotate under normal running conditions.

The car is not overheating and reasonably quickly gets to 90 degrees on the gauge where it remains (so there is a chance that the car is not switching on the fan because it doesn't need extra cooling). Still no air con.

If I disconnect either of the temperature sensors the fans both rotate at full speed.

My understanding is that this is correct. Logically, then it seems to me that because this happens the command wire from the ecu must have integrity as it does cause the fans to operate when the cooling sensor information to the ecu is removed.

Unless there is a fuse that I have missed (bearing in mind that the voltages at the connector for the cooling fan unit are correct), there is command from the command wire (when sensors disconnected) then all i am left with is an ecu fault which at the cars age and mileage will condemn the car to the scrapheap (a real shame because the rest of the car is great) and after owning it since 2008 I will be sad to have to do this.

For what it's worth I don't think it's an ecu fault (just a feeling.....loool) but I suppose it will have to be if I cannot find anything else. From what i can gather broken command wire is common where the wiring loom passes near and around the stater mot and underneath the battery tray but as i said above the fans turn on when the sensors are disconnected so i do believe this indicates that the command wire is good.

I think the car needs to be looked at by vcds but, of course I don't have that access.

So, if anyone out there can offer advice/possible solutions I would be very grateful.

Thanks all Regards

Tom

Edited 3 hours ago3 hr by ThomasP

The way I'm reading this is that the only reason to think the fan system isn't working correctly is that switching on the A/C doesn't trigger movement.

Might there not be other faults in the A/C system that are meaning it doesn't work?

I have VCDS and would be happy to plug it in, but we're not neighbours, I live near Swindon. I do pass near you, I guess, from time to time when visiting family members in East Anglia though.

Pete

As usual thx for responding and taking an interest I really do appreciate it.

Yes, I agree. I almost put your thought into the update post.

I agree it could be that there is a separate a/c problem and that is a fact, it's just that I think the change in the way the car warms up and the failure of the a/c seemed to coincide but I may be wrong. It's just that the cooling fan NEVER comes on and I don't become aware of any fan operating at any time during my local, non traffic jam and up and down the A1M to the next junction type driving driving. Evrn n this incredible heat we've been having the temp gauge has just remain bang on normal.

Thanks also for the offer to plug in to vcds and when all options are exhausted through this forum if it's ok I may take you up on that.

Are my conclusions correct in the previous post regarding the command wire or could it still be a wiring fault?

Perhaps there is a relay that's gone faulty when I switch the air con on.....? I just don't know

Regards

Tom

When was the coolant pump last changed?

It's a while but I always have it changed with the timing belt