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Discussion Starter #1
I'm after a pointer on where to find the temp sender that drives the ECU cooling fan control input - let me explain... in case someone has a better idea!

My 156 2.5 V6 normally runs at between 80 and 90deg whatever the traffic/use, however it has recently started to get to over 100deg in traffic, fans cut in and bring it down again. With the a/con on and stationary it sits nicely at 90deg (fans pulse on and off) and at any speed above about 40 it also sits below 90deg.

Did a bit of diagnosis at the weekend and found a few things out:

1. Both fans should run together, whether slow or fast, and whether driven by the a/con or coolant temp.
2. There are 2 x 50A black relays (in the group in front of the battery) that drive the fans - 1 for fast (the rear left hand relay) and 1 for slow (the one to the right of it). Each relay drives both fans.
3. There are two resistors on the panel behind the radiator, one in each of the fans' slow speed circuit (to regulate the speed) - the upper one of mine has failed, so until I shorted across it, I had no n/s slow speed fan.
4. Whilst my slow speed fans used to cut in at just over 90deg (a/con off), they now cut in at around 105-110deg.

My diagnosis: I only had one fan working at slow speed so need to replace a resistor, but without the a/con on (which I understand uses an a/con gas pressure sensor switch to drive the ECU to turn the fans on) there is no drive signal to the fans until coolant temp reaches 105-110deg (on the dial).
From other threads it seems the V6 has 2 temp sensors, one feeding the temp display dial and the other the ECU uses to drive the fans. So my conclusion is that the one feeding the dial is ok, the one feeding the ECU is on the way out and is under-reading.

Problem is, I can't find them - anyone help??:confused: Thanks
 

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Discussion Starter #3
Thanks Pud237 - nice carpet!

Read the thread the other day before I started digging around on my own car and it helped work out where to start, but I still come back to needing to find the temp sender.

I'd already jumpered between the resistor terminals so at "slow" speed drive the fan with the failed resistor runs fast - the problem is the ECU isn't turning them on a slow speed until about 105deg!
 

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Not sure where the temp sensor is - I never got to that stage as I found my problems was due to a wire melting on the exhaust and shorting out.

Really not sure what you should try, the temp sensor isn't a usual fail item though.
 

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Consulting eLearn I've gleaned the following information ...


The V6 has 2 temperature senders...
1. the first is on the thermostat, this only drives the temp gauge.
2. the second is in/on the injection unit which drives the ECU

If you disconnect the sender on the injection unit this should put the ECU into "panic mode" and switch on the fans all the time ...
 

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I know on the JTD that the pipe that passes the coolant from the stat to the injection unit is very small (in comparison to the other coolant pipes) ... I presume it's only purpose is so that the sender in the injection unit can do it's job ... so maybe it's become a bit blocked (just clutching at straws though ...)
 

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Discussion Starter #7
Thanks for that Chris.

Will have a look round for the Injection Unit, though not sure exactly what I'm looking for :confused: - presumably the electronics until that controls the injectors, so tracing the wiring back from the injectors should find it?

From what I could see, there was NO electrical connector coming from the thermostat housing, though I really ought to take off the intake plenum chamber to get a proper look. I do remember seeing a small hose around the area of the thermostat housing though, so hopefully that is the feed for the injection unit temp sensor and I can trrace it along to find it - again will need to take off the intake to get a proper look.

That's the problem on the V6 - it's so tight under the bonnet that finding or inspecting anything is a job in itself!
 

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Discussion Starter #9
Hi Maxitore.
Yes I did get it sorted, eventually - with the onset of autumn and cooler weather I never seemed to get stuck in traffic long enough for the temp to rise a lot - so I left it. Then a few months ago my cambelt was due replacement, so when it was in at Benalfa I asked Alan to change the sensor and slow speed resistor. Back to 90 on the button now in the hot weather.

I should also mention that after that last post I had another good dig around the fans etc and found that the 2 bolts securing the O/s of the fan mounting frame to the radiator has fallen out!
This allowed the fan frame to flap about, no doubt reducing the effectiveness of the fans, and a bolt had chafed one of the fan supply wires so I think I also had an intermittent open-circuit. Impossible to be sure exactly what was going on with the combination of factors, but am fairly sure the fans had not been loose all the time and that they didnt even switch on before 95deg, so the new temp sender sorted that and the wire repair, new bolts and resistor mean it all works all the time now too!
So with that done, new cambelt and having had bonnet, roof and sills repainted - dulled finish, rust and rust respectively - I'm now hoping to keep her going for another 136k!!

or til the next 'belt change at least :)
 
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