Hi All,

need some advice. The Radiator fan is permanently on when the engine is on/electrics on. The garage initially thought it was the thermostat so changed that. then they changed the sensor going into the engine. finally they removed the fusebox and gave all the contacts a clean - still no joy.:bang::bang:

when hooked up to the test box, the tests can control the fan speed etc, but then reports:

Fan Control #2 - Open Circuit

needless to say, they cant tell where/what Unit #2 is. Fan #1 control reports no error.

do any of you have any ideas what it reporting as failed? the thermostat was 2nd-hand from the looks of it.

getting desperate and need any pointers so the garage can get its head around the problem.

Help!!!

many thanks, bb

Bigbuddha36 said:

The Radiator fan is permanently on when the engine is on/electrics on. The garage initially thought it was the thermostat so changed that. then they changed the sensor going into the engine. finally they removed the fusebox and gave all the contacts a clean - still no joy.

Click to expand...

If the fan is running permanently, even when the engine is cold, then it can't be a problem with the thermostat, so a waste of time and money replacing it. Engine temperature sensor is very easy to test, so a waste of time and money replacing that too. Diagnosis by substitution will be expensive, so I think you need a different garage.

The fan control circuit is different for different engine versions. What engine do you have?
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Hi,

its a 2003 jtd. the garage are paying as it was part of the deal, but hanging around whilst they fail is stupid - thought id ask someone who would know. they hooked the diaganostics on it and it came back with that fault but they dont understand what control unit #2 is

The JTD engine cooling fan is controlled by an ECU mounted inside the rear radiator cowling. Remove the screw and the ECU comes out attached to the plastic panel. Be careful not to disturb, hit or damage the early crash sensor mounted above it (green sensor with yellow connector).

Your problem could be caused by water inside the grey engine fuse box. This is more likely if the large black plastic battery cover is missing. Your garage would need to seperate the two halves of the fuse box to dry it out fully. There's a guide how to do it here: https://www.fiatforum.com/stilo-guides/313986-how-clean-dry-out-fuse-box-near-battery.html
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They did that! - i did question the sensor as it was 2nd-hand but both the old & "new" broken in the same way??

they swapped the thermo - sits up by the top of rad & connects under fusebox etc, they changed the temp sensor into the engine & then cleaned the box (took it apart etc)

the diagnostics say fan control #2 open circuit

So they need to check for open circuits in the ECU wiring. Most likely culprit is the black connector shown at the 11 o'clock position in my picture of the ECU. It connects to a loose plug in the battery box, hanging under the grey fuse box.

EDIT: What do you mean by; "thermo - sits up by the top of rad & connects under fusebox"

incidentally, i recognize the 2nd pic as the part they replaced, but not the green block - is that separate to the silver block&cables? - if so, then I don't believe they changed that. - could that be the culprit?

Getting confused now...... You said they'd replaced the thermostat, (which is an aluminium housing mounted on the end of the cylinder head that all the coolant hoses connect to), and the sensor to the engine, (which is the engine temperature sensor that screws into the thermostat housing).

You said the "test box" reports fan control but they cant tell where/what it is. Now you say they replaced the ECU, (which is the fan control).

There is only one cooling fan ECU on the JTD. It controls all fan speeds. Other engine versions have two fan speeds controlled by the engine management ECU and two relays. If your garage's diagnostic equipment (test box) is reporting two fan controls, then they probably have it set to the wrong engine.

The green sensor in my first picture is a crash sensor that sends a signal to the airbag ECU to fire the airbags in the event of a crash. It's nothing to do with the engine cooling system. I only mentioned it in post 4 to warn you, or your garage, not to disturb it while working on the nearby cooling fan ECU.
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If they said they will fix it as part of the deal then demand they take the car to get diagnosed/repaired correctly at a Fiat dealership. This is common practice.

sorry, thermostat is my poor description. the part that they changes was the ecu (pic 1). I've passed on your suggestion about the connections under the fusebox. They have access to a specialist (apparently) from another garage over the road - this was obviously a fault that has gone beyond their capabilities. Since I sat there for 4hrs watching trail&error, i figured i'd ask here so i dont have to repeat this again when i take it back.