00705 - Relay for Coolant Fan; Stage 1 (J279) 31-00 - Open or Short to Ground

[devonutopia]

This is a new fault popping up on the mongrel in module 08

 

Has anyone seen this before and would know where to look first?  Secretly hoping just relay 279 is up the spout, but would this cause this fault as I know traditionally an open/short to ground is usually broken wiring.

 

This time of year I don't think the fan is cutting in, so I am not seeing anything get hot.  I am concerned for my trackday on 1st Feb though if the fan isn't cutting in at all....

[Breezy_Pete]

J279 is the low-speed relay within the fan control unit on the nearside chassis leg near the rad thermoswitch.

Check the relevant fuse (one of the blade fuses near the strip fuses on battery ISTR, 30 amp).
Check that the wiring looks undamaged and connector sealing OK.

If all that checks out, try another module.

[philmae]

Hello,

 

Did you find a solution to your problem?

I got the same and already changed the J293 fan control unit, but I've got the same error.

[Breezy_Pete]

Have you checked the fuses under the little cover next to the row of strip fuses above the battery?

 

The fuse for low speed operation of the fans is no. 8 (30 amps), the second of the blade fuses under the removable cover to the right of the strip fuses:

 

[Breezy_Pete]

It's quite possible that both fans have burnt out their low-speed resistors, see here: http://www.briskoda.net/forums/topic/404143-radiator-fan-repair-courtesy-of-vortex-here-and-uk-mkiv-forum/?view=getnewpost

[philmae]

Hello,

 

Just for the record in this right topic, so it can help anyone else :

 

I've got a Skoda Fabia 1.9 TDI Mk1 (year 2000).

 

The only fault I find on VDCS is the following :
00705 Relay for Coolant Fan; Stage 1 (J279)
009 Open or Shortb to Groud

 

So there is a problem with the low speed of the radiator fans.

Indeed, when I turn the A/C on, the fan should start at constant low speed but it does not. It just goes ON at full high speed when the Climatronic detects a high pressure. So it does not turn for 15 seconds, then turns full speed for 5 seconds, then turns off again 15 seconds, and so on.

 

As a result, my A/C still works but intermittently : fresh air, then less fresh air, fresh air again... Very annoying because it's not enough in summer days.

Following the workshop manual I should check the wiring going to the J279, and if everything is fine, I should change the J293 fan control module :

http://workshop-manu...ii/fault_table/

 

The module is about 45€ and the car is 16 years old, so I didn't want to lose expensive garage time to find something that could not be there, and just asked them to change the module. It didn't change anything, so I did a mistake and should have checked the wiring first...

 

So, I am wondering :

- Is it possible that this error occurs if there is a wiring problem between the fan controle module and the fans, or if the low speed of the 2 fans is broken? Would it perhaps help if I disconnect the fans from the module and see if I get the same error for the high speed relay. If not, it's certainly a problem only between the module and the Climatronic, as I would expect.

- Would it help if I dismantle the Climatronic module inside the car? I doubt so.

- Where does exactly the cable harness going to the fan control module pass through the car, so I can check the maximum myself before going to the garage?

What I've already checked :

- The secondary fuses on the battery with a multimeter : they are fine.

- No corrosion detected on the connectors connected to the J293 module.

 

The number of posts on the Internet concerning this J279 fault is really low, so I would be happy if you could help me.

What do you think?

Edited 25 October, 2016 by philmae

[Breezy_Pete]

I suspect the fans themselves; do you have a multimeter?

 

I found that measuring between the pins of the (disconnected) fan plugs showed that I had high resistance between the low-speed wire (middle one) and ground (brown wire), indicating that the internal resistor in the fan had blown. The plugs I'm referring to are the ones on a little bracket near the bottom corner of the radiator, better access from below.

 

Do both of your fans have three wires going into the 'heart' of the fan?

Edited 25 October, 2016 by Wino

[philmae]

I just checked and yes, they both have 3 wires connected to them. And they both act the same way : full speed on high A/C pressure.

Does it change your diagnostic?

I will try to disconnect both fans from the module to see if another fault comes on and check the resistance as you said to eliminate a fan problem. What should the right resistance be?

[Breezy_Pete]

I think later cars went to a single speed AC fan, which will not be vulnerable to the low speed resistor failing, 'cos there isn't one!  The correct resistance would be a few Ohms, single figures I think.

 

As both are in parallel, you can measure the resistance of both at the same time via the large connector of the fan module, without having to disconnect individually.  If both have lost their low speed resistor, a high resistance reading will be seen.

 

I'll try to find an image which shows which pin of that connector to measure with respect to chassis ground.

 

I think it's the one nearest the latch in this photo:

 

[philmae]

Yes, it it this connector. Good idea, I will try as I can try to access it through near the fog light.

Do you also know which color is the wire that controls the J279 low speed, on the second little other connector? I was not able to find it, never sure it was the good diagram for my car. I really suspect it to be the problem and I could check if I get 12V on it while A/C is on and if I get 12V on the high speed control wire when it turns on.

Edited 25 October, 2016 by philmae

[Breezy_Pete]

Pins 5 and 6 of the small connector go through to the HVAC module in the cabin, for 'intelligent' control of the fans. I'm popping home shortly to where I have a module in bits, but I'm reasonably sure that to switch the relays/fans on, these wires are pulled down to ground by the HVAC module, rather than taken up to 12V.

 

If you click on my image above to enlarge it, the wires in question are labelled K1, K2 on the side of the module. The ones nearest the front of the car.

The radiator thermoswitch does the same 'pulling down to ground' of the middle wires of that connector, for 'unintelligent' fan activation. 

 

I've sketched a little circuit somewhere, will try to find it later.

Edited 25 October, 2016 by Wino

[philmae]

I just found a weird thing : my engine code is ATD and the car has been bought in december 2000.

When I look at the flux current diagram, for the ATD version of February 2000, I find this :

 

 

The J279 is not wired!

But this diagram is not applicable to models with air conditioning.

Okey, but I cannot find any other diagram for my ATD model with air conditioning, even from other years.

 

 

Edited 25 October, 2016 by philmae

[Breezy_Pete]

Can't see your image?

[philmae]

Just edited my post 

Edited 25 October, 2016 by philmae

[philmae]

Oups, OK, I found it in the "Air conditionning" part of the current flux diagram, for the 2000 models :

 

[Breezy_Pete]

Try diagram 19/1 onwards, or maybe 53/1 onwards, but I think they're much the same.

Edit: I see you've got there, well done.

 

Will post up the internal wiring of J293 pic in a minute or ten.

Edited 25 October, 2016 by Wino

[Breezy_Pete]

Let me know if you can't read my pathetic handwriting...

 

[philmae]

Very clear after analysis, thank you!

 

OK, so as the error is an "open or short to the ground" to the relay J279, it seems that the wire K1 (5) is clearly broken : the brown/blue.

And if it was to the ground, the fan would turn on permanently at low speed.

 

To test the low speed of the fans, I could also try to make the radiator hot enough to get to stage 1. If I only get the same level 2 high speed, it is that the fans have a problem.

Does it sound right and how can I do this? Should I run the motor @ 2000 rpm for a while to get the radiator very hot, with A/C off?

 

What do you think?

Do I finally have no other choice, after tesing the fans are ok (or not) to go to the garage and check all the wires from the J293 to the Climatronic control module?

Edited 25 October, 2016 by philmae

[Breezy_Pete]

You can (try to) trigger the low speed fan operation by shorting pins 1 to 2 of the thermoswitch (F18) connector that are on the ends of the brown wire and brown/blue wire in your diagram above. (Grounding MOT1 in my scribble)

 

I suspect it won't cause any fan operation, because the internal fan resistors are probably history (but easily repaired with external resistors, as you've seen?).

 

I think the fault code reported is an inference, rather than a fact, if you see what I mean.  The coolant temperature/refrigerant pressure doesn't stop increasing after the low speed relay is triggered, so the ECU 'assumes' that there's a problem with the electrics on its side of the relays, cos that's all it knows about?

Edited 25 October, 2016 by Wino

[philmae]

Yes, you are probably right.

I will check everything we mentionned and come back to give experience.

 

Waiting that, thank you very much for your help!

[philmae]

Just another question : if the low speed of the two fans is dead, does that mean that I will have to change them or can I do something easy to fix the resistors?

Like bypassing the low speed wire with a resistor to the high speed one?

[Breezy_Pete]

You've got the idea. Here's one example of the workaround. There are a couple of other relevant threads in the link I gave you in post #5 above.  It may be easier to change the fans, as they are 16 years old now, but obviously that will cost a lot more than DIY wiring in of some big resistors.

[philmae]

Hello,

 

I finally went to the garage.

We tried to shortcut the 2 speeds of the coolant fans by using a little cable on the fans' connector to the relay module, it did some sparkles  but the two speeds are working!

 

So the error must be relevant, and the problem seems to really be between the relay module and the climatronic.

The wires near the "command' connector of the module seems OK and no rust.

 

What do you think? Should I try to see behing the climatronic module, inside the vehicle?

[Breezy_Pete]

Yes. I think if you can unplug the 16-pin connector that takes these two wires into the HVAC module, and short each in turn to chassis/ground you should see the fans come on at each speed. Ignition will need to be switched on for the high speed.

A strange thing about the wiring of these is that the wire colours swap over halfway from HVAC module to fan control module, at the connector blocks which take the wiring through from cabin to engine bay. Brown/blue becomes brown/green and vice versa. Seems strange. That's what the current flow diagram says, not sure whether it is true in reality.
Pin 3 of HVAC goes to pin 5 of fan control module for low speed fans and pin 6 of HVAC module goes to pin 6 of fan control module for high speed fans (when ignition is on).

 

Seems unlikely to me that both wires would be broken, so I think this test should result in correct fan operation, meaning the fault is within the HVAC module, I think.    Edit: just reminded myself that it's only the low speed operation that you are having trouble with so ignore that crossed out bit.  Concentrate on the wire from pin 3 of the HVAC 16-way connector it should be brown/green at that point according to the CFD.

I'll try to have another look at an HVAC module I have in bits to see what these two wires actually connect to on the circuit board within.

 

Not too hard to work out, once I realised it was a four-layer board due to the absence of tracks on either outer layer from pin 3. Each pin goes to a FET transistor that is in turn driven by the main 'brain' microcontroller on the board.

 

Edited 29 November, 2016 by Wino

[philmae]

Thank you very much for all this information!

I will try to dissamble the HVAC unit from the inside, seems to be pretty easy if I'm not wrong, make the test and take a look at this FETs.

I will post my results here, hope it can help anyone else.

See you soon!