Engine bay cooling Fan comes on with ignition

Been down a right old rabbit hole on with this one. , but a problem of my own making

My engine fan is constantly running with the ignition on,  checked the normal stuff.  Ambient temperature probe , Connector and any cable breaks and relay
All good so far , Trawled through the electrical diagrams , after much puzzlement, i eventually spotted the cable colours are wrong , and the connector fits but not quite right , which i assumed that at time was because the metal clip was missing.

A little background to help follow where I've got to , My car is a MK2 F,  I've replaced the loom with a TF Loom and its now has a Pectron BCU instead of Lucas , so infact my car is now of the type where the Ambient Temperature probe has been deleted.

Now i've worked that out, the Question (finally) , if the connector below isn't for the Ambient sensor where does it actually go?  Cable is Green with black trace

 


 

I’ve come in, locked the workshop, finish for the day & have left my diagrams in there. But considering where it is, the history of the car & the type of connector, have a look at the factory fit low coolant sensor circuitry.
Just a thought.
M

That's a good shout, can't currently see reference to that in any of my diagrams,  connector on the level sensor looks like a match.
However if it is that ,  I'm no closer sorting out the engine bay fan.

We need Roverlike to stop by.

I agree!
Direct and purposeful analysis of the problem and almost always a solution.
This place is amazing.

I’ve just had a closer look at your photograph & I would say that’s light green/black, I’ve been looking for green green. (!)
The only green/black & black paired is associated with the fuel pump, nore have I found any reference to the low coolant system or wiring.
I’ll scan through again & see if I can find any correlation with your problem.
I’m in the midst of torturing some metal into submission, a little more pressure should persuade it to take on a form similar to the drawing. The fight isn’t over just yet, I’ll look later.
M

My Current thoughts are, 

That connector (as suggested) is for the coolant level alarm which i think was introduced into the loom late 2004,  But the sensor not fitted by default until the SAIC models. At the same time the Engine bay Temperature Sensor sensor was deleted.

The connector exits the body loom at the at the same place as the Temperature sensor connector would have done,  the only place it can reach is either the Temperature sensor or the Coolant level sensor,  Cables are the wrong colour for the Temperature sensor,  If it went to the engine it would be in the Engine Harness (so it wasn't effect by movement), That only leaves the Coolant Level sensor as the viable option.

I thought i had traced the cable back to the top connector on the ECU, but couldn't get any continuity on the cable , In fact it appeared to be grounded at the ECU, as the colours are much same, i'm assuming i was actually buzzing out the Fuel circuit and not the connector i thought i was testing.

I'll short the pins on the connector when i next get chance,  I have the SAIC instrument cluster so in theory the Coolant light should come on.  If so that's is of course a bonus, will just need a different coolant bottle (all though they are stupidly expensive)  

Surprisingly there is no mention of the level sensor within the 2009 server Manual (actually i'm that surprised really)

Circling back to the problem that highlighted all of this.
With the Engine Bay Fan constantly running it means the ECU is going into fail safe because its not seeing the sensor it wants to see. I believe this function was moved to one of the coolant temperature sensors on the engine , I can ignore the body mounted Air temperature as that's now historic (and a total red herring a this point), 

I'm thinking there must have been a engine harness change between the MY2000 MGF and the late 2004 MG TF's , Its occurred to me my harness has the connector for the Pre Cat CO2 sensor , which would be missing on a Later TF , so thats one change i can think of,  So reasonable to assume its also missing the splice that feed the coolant Temperature back the Engine Bay Fan control.

Of course could be sensor failure, but i figure more likely harness changes at this point.

Also my alternator doesn't appear to be working, (i need to put a meter across it) , I assumed that was because it had a 14 year sleep and the regulator had probably died, but could also be engine harness.

Then two last jobs before MOT time (finally) ,  Quick bit of cable joining to turn the SRS light of on the SAIC instrument cluster and work out how to turn the ABS light off, Car thinks it has ABS , it doesn't, it does have the wiring but not the pump or Hubs.

I’m refurbishing the cockpit at the moment (amongst other evidence of stupidity). Ages ago I fitted override switches on the cooling fans & I was testing the repositioned windows controls, which worked (hurrah) I did a rundown of other things changed recently. My engine bay cooling fan won’t override; Bugger.
I’ll be resolving that irritation tomorrow, it might help with your problem. I’ll keep you posted.
M

Doesn't the ecu control the fans from the coolant temp sensor, both radfans and engine bay on later TFs.
Why wouldn't a 2004 Tf have a pre cat O2 sensor? I don't follow that... it should have pre and post sensors like the mk2F, mems3.
Don't forget the alternator fuse, worth a check :yesnod:

That is my understanding,  After a bit of research I'm wondering if my ECU is to early and looking for the AAT sensor,   I'm currently unsure if all Pektron cars used the coolant sensor or if some still used the AAT sensor.

Think i read somewhere about the pre cat sensor, but yep doesn't make sense, so probably wrong.

That'll teach me for having right mixed bag of stuff.

psymon wrote:

That is my understanding,  After a bit of research I'm wondering if my ECU is to early and looking for the AAT sensor,   I'm currently unsure if all Pektron cars used the coolant sensor or if some still used the AAT sensor.

Think i read somewhere about the pre cat sensor, but yep doesn't make sense, so probably wrong.

That'll teach me for having right mixed bag of stuff.

Engine bay air temperature sensor was deleted in mid/second half of 2004 starting from VIN RD 634869 in the same time when low coolant sensor was fitted to expansion tank on MG TF cars.

MG TF from VIN RD 632424 to RD 634868 had low coolant alarm wiring fitted but no sensor fitted to expansion tank and therefor you would have checking of low coolant alarm triggered but no sensor - action was needed by T4 to electronicaly shut down that check.

It doesn’t matter who asks the question & about whichever problem, if Roverlike gives an reply I always feel as if my knowledge expands two fold.
Sir, I take my hat off to you & your encyclopaedic knowledge.
So does that resolve the problem; the wire is there & its hoping for sensor, which it doesn’t have. The MEMs CPU thinks, therefore, that the coolant is low, thus turning the fan on to compensate for a possible rise in temperature.
Or is that an oversimplification?
M