VN 1990 thermo fan not switching on.

[Gesty]

Hi everyone. I was wondering if anyone has some info regarding the location of the temperature sensor? which sends power to the relay to switch on the thermo fan? I can hot wire it with a switch going in to the cab but I would prefer to fix the sensor or at lease put a switch on a wire controlled by key.

Thanks heaps.

Gesty

[peter65]

hmmm i think that the switch (its an on/off, not like the temp gauge sensor whose resistance changes in proportion to the coolant temperature) is behind the alternator... if you want to wait i will have alook in "the book" tonight.... cheers peter...

[immortality]

the thermo fans is controlled from the ecu. there are 2 temp sensorson the ngine manifold. one forthe ecu and one for the gauge. better to just fix it. try swapping the relay with another and see if it works then, have you checked the fuse?

[peter65]

hey gesty. had a look at the book (when all else fails....). this is for avp, V6. the fan switch is locvated behind the alternator (remove drive belt, hinge alternator up). there are two devices there: the fan switch is on the passengers side. the other one is the temp sauge sensor.

as immortality said, swap the relays first (probably with the horn one - i think they are the same).

To test the fan cct, short terminals A and B on the diagnosis connenctor with a wire link - the fan should run. The diag connector is in the front passender footwell behind a kick panel.

If the fan doesnt run - check the 2 fuses: #9 (in the engine bay fuse block, the fan relay coil fuse) and #23 (the fan motor fuse which i think is in the main fuse box in the cabin).

the fan motor cct is:
batt to fuse 23;
fuse 23 to relay terminal #30 (orange/pink wire);
relay terminal #87 to fan (orange/blue wire which becomes a blue wire mid path);
From the fan to earth (doesnt say what wire colour but probably black).

the fan relay coil cct is:
batt to fuse 9;
fuse 9 to relay terminal 86 (pink/white wire);
relay term 85 to ecu term c1 (blue/white wire).
Both wires from the coolant temp switch go to the ecu (yellow to ecu c10 & black/yellow to ecu d2). note that the cct says that this wire also goes to a throttle position switch. not sure where this is.

hope this helps... pete.

[VNCalais98K]

Hey this is gold..

My thermo only works when i switch AC on. I have new thermostat and temp guage works fine, so I have been trying to find out where the fan gets its on/off temp signal from...

So to change this i need to remove the alternator?

Also, is the part number the same as the temp sensor at the back where the guage reads from?

Once i fix this up and change the heater switch in the engine bay My car will be set! woo.

[peter65]

hey there. you dont need to remove the alternator, just remove the serpentine belt (loosen the belt tensioner and the belts pops off - rememeber which way it goes back on - draw a pic if you have to!) and then undo the drivers side alternator bolt, loosen the passengers side one, and hinge the alternator up towards the passngers side. you can now see the two sensors and they are different. the one you want is on the passengers side. pete

[VNCalais98K]

Any idea of a part number? or should the local sprints know what i need? (haha.. yeah right)

[VNCalais98K]

Ahhh bloody sprints say that the VN doesnt even have a switch in that location.. and i dont want to pull it out to prove it or else how can i drive to get a replacement... ruddy hell.

[Cheap6]

The ECM temperature input, from a sensor not a switch, is via a resistor that varies resistance with temperature. The ECM also uses it for a few things other than determining when the engine cooling fan shoud be on.

The ECM itself may be at fault too. The ECM switches (internally) another resistor at a particular temperature reading. A common fault with early VN ECMs was a cracked printed circuit board preventing that resistor from being part of the circuit and hence an incorrect temp reading.

There are two locations for the sensors (the gauge sender and ECM sensor are adjacent in each case); early VN have them at the rear of the engine, later models under the alternator.

I feel we're reinventing he wheel here too: try Wiring up a switch to the thermo fan?

[VNCalais98K]

ok, so im back to square one.
The temp sensor works fine, i get a proper reading to the guage and everything, but the thermo fan doesnt switch on automatically, but it DOES when i have the A/C on.

So its not a dead fuse, its not a dead fan, and its not a dead sensor...

So you're suggesting i replace the computer?

[immortality]

ok, so im back to square one.
The temp sensor works fine, i get a proper reading to the guage and everything, but the thermo fan doesnt switch on automatically, but it DOES when i have the A/C on.

So its not a dead fuse, its not a dead fan, and its not a dead sensor...

So you're suggesting i replace the computer?

one thing that will tell you for certain if the ecu is the problem is to use a diagnostic cable for the ecu and hook up to a laptop. get yourself a copy of
WINALDL and then you will be able to see exactly what the ecu is doing. have you checked for fault codes. if it works when the a/c is on then all the thermo fan wiring is fine. all it can be is the temp sensor in the manifold,wiring for said sensor or a ecu problem. the sensor for the ecu is seperate for the gauge so just because your gauge is reading fine doesn't mean the one for the ecu is. is it using a lot of fuel at the mo?

[Cheap6]

So you're suggesting i replace the computer?

No! I was suggesting that may be a possible fault. The scan tool/cable Immortality is talking about will tell you what the ECM thinks the temp. is and if it is outside the expected range and setting a fault code.

For a one off ie. you are not going to use the cable for anything else it may be cheaper to buy an ECM from a wrecker as a diagnostic aid - they are pretty cheap. Borrowing one to try from a mate is even cheaper.

The sensor for the ECM can be ID'd by the blue plastic two pin plug. The same coolant temp sensor is used in a variety of GM models; Camira, Astra, Pulsar, Commodore V6, V8, as is the ECM, but the 'chip' - memcal, the blue plastic block inside the ECM case - needs to be swapped to match. That info may get you a cheaper ECM if you go that route.

From my 'shop manual the coolant temp sensor should have the following resistance vs temp.:

20C = 2500 ohms
30C = 1800 ohms
40C = 1200 ohms
70 = 450 ohms
90 = 250 ohms
100 = 190 ohms

Normal operating temp. for VN is 98-103C

[VNCalais98K]

one thing that will tell you for certain if the ecu is the problem is to use a diagnostic cable for the ecu and hook up to a laptop. get yourself a copy of
WINALDL and then you will be able to see exactly what the ecu is doing. have you checked for fault codes. if it works when the a/c is on then all the thermo fan wiring is fine. all it can be is the temp sensor in the manifold,wiring for said sensor or a ecu problem. the sensor for the ecu is seperate for the gauge so just because your gauge is reading fine doesn't mean the one for the ecu is. is it using a lot of fuel at the mo?

bout 13.5/100Km city.
I guess it is a little higher...

Well the temp sensore for the guage is the one that is most obvious when you look at the rear of the manifold right? 1 green wire going to it?

So which is the one for the ECU reading? anyone have picture? diagram?

Sorry to be a pain but i dont have a manual.

[Shifty1]

I'd like to know this also.. my dads thermo doesnt come on (90 VN V6) but it does come on when the A/C is on..

[VNCalais98K]

Dodgy VN's/ haha.

Mines 88... series 1 POS.

[Shifty1]

Mins a S2 S Pac..

runs real warm most days when idling.. that gave away the no thermo operation..

[VNCalais98K]

It should come on at just over half.

[immortality]

the series one engine (thermostat under the the elbow for the TB. there are 3 sensors there, black plug - temp gauge, grey plug - MAT, blue plug temp sensor for ecu

[Cheap6]

The resistances I quoted earlier are across the two pins of the (blue plug) sensor. I would say that 13.5l/100km, city is about right.

[VNCalais98K]

Immortality... If I you were a chick i'd kiss you!

That photo is FANTASTIC

Answers my question PERFECTLY!

All those plugs got drenched when the manifold corroded through, so i wouldnt be surprised if theres a failure or 2.

The temp guage sensor on mine has a bad connection, so when i wiggle it the guage will go funny, but the ECU temp sensor is in a bitch of a place init.

oh well, ill tackle that on the weekend.

So if the sesor is faulty and the ECU is probably getting a cold signal all the time which would make it run rich, doing a few things,
1) Increase consumption (its sitting at 14.4 for city now.. it used to show instant 7.5 for cruising at 60, now it shows more 9 or 10)
2) Run slightly poorer
3) Run Hotter (also if its rich, it would run hotter at idle than with revs so would also explain i little why it cools more when you rev it than when its just idling)

Well that explains a lot.

[VNCalais98K]

Well y weekdn is all planned out then...
Drain and flush coolant.
replace sensor and heater tap.
Refill coolant.
Change oil and filter
Enjoy a nice beer.

Hope saturday is going to be cool.

[immortality]

if you haven't done the thermostat lately then i recomend doing that at the same time, pull the TB and elbow off to give yourself lots of room, clean the TB with some carb cleaner also.

[VNCalais98K]

thermo was changed in october.
TB was cleaned out september.

[VNCalais98K]

Well looks like I got in too late.

On friday the car didnt want to start, spluttered a bit ran on a couple of cylinders, bit of black smoke, but after 20 secs or so came good.
Saturday night had a bit of a splutter came good but would splutter a bit when you gave it some revs then kick in.

Sunday the car started fine but then as soon as i actually went to take off it flooded out and started spluttering on 2 or 3 cyls again, with some black smoke etc.. then after about 2 minutes came good again...

My theory is that the temp sensor is fragged giving it a dead cold signal all the time and the ECU is compensating by loading it up with fuel, which is causing the flooding, black smoke and has probably fouled up the plugs some too.
Other than that the only other thing would be the coils, but we'll try the sensor and plugs first because theyre cheaper... haha.

So anyway.. i bused it into work today and wont get my car seen to until wednesday (i dont have time to do it myself)

[stockyvrcalais]

hey all, sorry to dig up such an old thread but when i bridge out the black & white wires on diagnostic plug my a/c fan does NOT come on, i know it works by putting direct power to it but why wouldnt it work otherwise? Any ideas would be great thanks.....