Need Help - Radiator Fan Issues while traveling, 2005 XC90 V8

PSVS · Post by **PSVS** » 27 Jun 2026, 08:22

Hello all,

Long time browser of this site, first post, XC90 owner for the past several years, and have been working on cars for 30+ years. I am over 1100 miles from home and need help.

I just drove my 2005 XC90 V8 from Toledo, Ohio, to Dallas, Texas over the past 32 hours or so. Did ~540 miles yesterday from Tennessee to Dallas, with much of the trip in 95+F degree weather. The radiator fan stopped working. Barely made it to the hotel (in Lewisville) as the temperature needle would creep above half when waiting at lights in 99F degree heat.

After the vehicle cooled down a bit last night, the fan started working again. I did some reading on various Volvo forums and groups last night, and without access to VIDA, it seems likely to be the fan control module.

- When the fan wasn't working, it did not work regardless of temperature or AC.
- The fact that it's now working again tells me it's not the motor itself.
- Jiggling the wiring harness doesn't make the fan stop, so I don't think there's a connection issue under the hood.
- I did not have the opportunity to test for +12V on the big red wire going to the fan when it was not working.
- Now that it's working, I can not diagnose anything without VIDA. (Or can I?)

I'm in Dallas for a week and will be renting a car regardless. Replacing the fan assembly is well within my skill set but too big of a job for the hotel parking lot. I'm considering my options:

- To just get me home, can I unplug the fan and just run a jumper wire or universal control module to it? If so, what are the terminals on the plug? Would having the harness unplugged from the fan cause any other issues, codes, errors? I would be driving more or less non-stop back to Ohio, and if I do stop could just pop the hood and disconnect the wire. I'd be replacing the fan assembly when I get home anyway.

- Is it a known thing for them to act funny when getting super hot, and is there a good chance, since it is working now, I can just drive it home and be fine? I plan to go back through Oklahoma, St. Louis, and Indianapolis, so it won't be the traffic hell of the route I took in (Cincinnati - Louisville - Nashville - Memphis - Little Rock).

- Can anyone recommend a trustworthy, competent, and fair Volvo shop on the north side of Dallas? If I can get the car fixed during the week and be ready to go . . .

All advice/help is appreciated.

Lastly, I apologize for my first post being a plea for help; in other car forums I belong to, I do my best to give more than receive.

Thank you,

Tony K.

Post by **ggleavitt** » 27 Jun 2026, 09:42

Did you do any code reads on this vehicle?
Fan is very variable, stops working, works, speeds up, slows down, all a function of what the ECM tells it to do via a signal (PWM).
ECM is looking at engine coolant temperature (ECT) sensor as well as the vehicle speed to tell the fan the speed to run. Dunno about bypassing, suppose you could wire it up on all the time but I'm not sure how you bypass the PWM speed control that connects to the ECM.
I'll guess something is being reported, might be good to get the vehicle read for codes first then you can decide how bad it is.

PSVS · Post by **PSVS** » 27 Jun 2026, 18:35

I forgot to mention -- there were no codes or warning lights/messages on the dash.

Post by **ggleavitt** » 27 Jun 2026, 22:10

K, so maybe the fan is working as it should. Coolant coming out of the reservoir cap to any degree? Temperature gauge on this vehicle is a purposefully neutered value, see thread as one example: https://www.swedespeed.com/threads/cool ... ge.705101/

Possible you can check with a local auto parts shop and see if they have a code reader that can pull the value from the engine coolant temperature sensor (ECT) and see what the ECM thinks is the temp.

ECM P01600_XC90.pdf: (298.71 KiB) Downloaded 39 times

The attached is what I think would have expected for an issued error if the ECM thought the vehicle was not cooling the engine properly. My fans do NOT run all the time, and sometimes they run super fast for no good reason. Purple wire in middle of the black/red is the PWM signal from the ECM, if you wait long enough you should see some variability to the fan speed, not just on/off. If you do a startup after warm, you should see the fan go faster for a minute maybe then settle down and in many cases just turn off. So if you see anything other than pure on/off, that suggests both fan and controller as functioning. At that point it's ECM doing the driving via that purple wire under a set of predefined criteria.

I did a cursory look on the interwebs (Google) using the term "volvo xc90 V8 engine coolant fan speed criteria". Maybe see what you get returned.

PSVS · Post by **PSVS** » 28 Jun 2026, 18:02

Thanks - this helps, and I've been reading some of your other posts on the topic before and after I posted this to get a better understanding of how the system works, and I appreciate your knowledge.

No coolant loss from the reservoir - none observed while running, no puddle, and level not lower than before after cooling down.

I'm surprised to see that thread about the gauge; when the fan wasn't running and I was sitting in traffic, at first the needle didn't move, but after a while it started to creep up when I was stuck at a light, and would go back down once I was moving again - it behaved more or less like one would expect the needle to behave. The hottest the needle got was two full hashmarks above the middle; had it gone anywhere near the red, I would have pulled over asap and sat it out until the engine cooled down and traffic was lighter. Luckily, each time it started to creep up, the light changed and we were able to move. Perhaps there is a wide temperature range at which the needle sits at the middle, and then only starts to climb once it gets over a certain temp?

When it was getting hot, the transmission also started to flare between shifts . . . I'm going to guess the radiator incorporates transmission cooling lines, too? Once I got moving and temps came back down, transmission went back to normal. (Regardless, I will be changing the transmission fluid the moment I get home.)

I'll look into the temp sensor, but any time in the past I have turned on the air conditioning, that would automatically turn on the fan, and the fan wasn't coming on even though the AC was on . . . so it doesn't seem like the first place to look, but I'll still look into it.