Radiator Fan Runs On If ignition Off

MisterWooley · Post by **MisterWooley** » 05 Jul 2018, 14:53

Hi, XC90 2004 D5 Diesel (UK)
Recently I replaced my thermostat unit, thermostat plus holder, to fix a coolant leak problem. Leak fixed, temperature always stable at correct value.
Now, during our little UK heatwave I have noticed that after switching off (hot) engine the radiator fan continues to run between 2-6 minutes. I have read that this is possible by design but I noticed tonight that if I leave the ignition on the fan slows to "just turning". Turn ignition off and fan revs to max. Turn ignition on and fans slows again.
There are no DTC's except CCM-0021Air quality sensor internal fault but that has been present since I bought the car many years ago. The fan problem is new (since thermostat changed).
I am puzzled as to why turning the ignition on slows the fan. I am wondering if I have a sensor fault and if so which.

Thanks

Post by **SuperHerman** » 05 Jul 2018, 18:13

I would keep an eye on the issue. Try your trick before driving the vehicle for the day. Once it cools down see if it still behaves in the same manner. On my 2004 XC90 T6 I have a fan run for a few minutes after the vehicle is shut down when ever it has been brought up to temperature - even in the winter. Has always behaved in this manner. Don't know which fan.

I suspect all is normal and the vehicle is cooling down due to high heat. Playing with the key as you mentioned changes things as another set of instructions (programming code) come into play.

Post by **oragex** » 05 Jul 2018, 18:50

Have you also tried one on http://volvoforums.org.uk/ ? Just in case but your D5 shouldn't be much different than petrols

But from what I've read on forums it isn't a normal thing (not the same as the cabin blower running for some time).

Is the thermostat genuine ? Also inspect the wires to the temp sensor near the connector

Post by **ggleavitt** » 05 Jul 2018, 21:30

Description (copy/paste)-
The engine cooling fan (FC) has two functions. One is to cool the engine compartment, the other is to cool the condenser when the air conditioning (A/C) compressor is working.
The engine control module (ECM) transmits a pulse width modulated (PWM) signal to the engine cooling fan (FC) control module. The control module then activates the fan at different speeds. The speed of the engine cooling fan (FC) is determined by the engine control module (ECM), depending on the coolant temperature (based on the signal from the engine coolant temperature (ECT) sensor) and the vehicle speed.
Note! The engine cooling fan may have a post-run of up to approx. 6 minutes after the engine has been turned off. The time for the fan's post-run depends on engine temperature, temperature in the engine compartment and pressure level in the AC-system.
Warning! Be careful since the engine cooling fan may have a post-run after the engine has been turned off.
The engine cooling fan (FC) and its control module are behind the radiator.
The engine control module (ECM) can diagnose the engine cooling fan. The fan can be activated using VIDA

Turning the car to POS I and hearing the fan speed drop to zero, suspect it's by some thought process rather than by a fault but it would be very good to review all the connections as the others have mentioned. Might be coincidence that you're hearing it around the same time you did a heat related repair and running the AC more than usual. Maybe...

edit- typo(s)

MisterWooley · Post by **MisterWooley** » 06 Jul 2018, 11:43

Thanks for comments and suggestions.
I did remove the sensor plug (on thermostat) check wires for obvious faults but none found. Refit plug. Thermostat is aftermarket.
After driving car today guess what. No more fan running on. Nothing else has changed.
Arguably not quite so hot today but still much hotter than usual (for UK)
Could I just have had a bad connection?
But surely if just a bad connection then the temp gauge would not indicate correctly.
Will keep an eye for on fan for a while and post any updates.
Thank you all

Post by **oragex** » 06 Jul 2018, 11:46

Do you remember which thermostat brand was installed?

Thermostat coolant sensors may not be the best.. may try put a used genuine one from the breakers see if the issue goes away? (the sensor may be removed using a deep socket I believe)

MisterWooley · Post by **MisterWooley** » 06 Jul 2018, 11:51

Thermostat was Calorstat by Vernet. I still have the one I removed. Genuine I think. Thermostat changed because of leak not sensor.
I could put the old sensor back and see how that works

Post by **ggleavitt** » 06 Jul 2018, 14:28

Oddly enough, a family member with a 2003 S80 2.9l non-turbo is experiencing fan run after shutoff until the battery discharges completely, at least that's how it's being described.

I'll head over tomorrow with VIDA and DICE, have a new ECT sensor lined up but entirely likely it'll be the fan assembly itself. Will update this post with resolution.

**7/7/18- Fan controller at fault, failed in the "on" position, key in or not. No other errors noted in VIDA, had purple wire to ECM off when tested. Pulled the fan power so car can be driven in an emergency, new fan assembly on order.

edit- add update vs new post, date

Post by **oragex** » 07 Jul 2018, 09:05

There a few discussions about Vernet on other forums (Bmw, Mercedes), not all agree about the quality but who knows in the end..

Does the temp needle raise steadily from cold to 12h in a smooth movement when warming up the engine?

The fan controller can also get faulty but I think it rather stops spinning than keeps spinning