Hey guys, I just picked up this 2012 S80 with 183K miles for $800. I had recently made a post here about a serious grinding noise and you guys were amazing (it was the motor mounts)

Now I just have one last issue to address, and it’s a weird one: The blower motor (fan) continuously turns on and off intermittently and randomly. If you have the dashboard light control turned all the way up the fan won’t work at all, but if you turn the dashboard lights all the way down it will work but intermittently. If I do other things power related (turning headlights on / off for example) it will cause the fan to shut off and then come back on again.

Sometimes it seems it may also be rpm / throttle related, other times you’ll just be sitting there idling and it will continuously turn off and on again over and over and over again, many times in the span of a few seconds. Sometimes it will work just fine and run flawlessly for a while.

one thing is for sure though: With the dashboard lights on high it doesn’t work, or hardly works.

I haven’t had enough time with the car to try other things, but obviously there’s an electrical short somewhere in the system.

I do have a lighting / bulb code on my dash, but I’m pretty sure all my lights work. I just ordered a high end OBD2 scanner because the one I have can’t fully scan the car, but I’m doubting it will be much help.

Any idea what this could be?

 

A good first step would be a scan that will talk to ALL the control units. You might have a bad resister - pain to replace but easier than the blower motor.

What lighting/bulb message do you have?

 

All I have for a scanner at the moment is a BlueDriver, but yesterday I ordered a Autel MaxiDiag MD806 pro which says it scans all systems. Did a lot of research and this one seemed the best for the price. I could have bought a Volvo specific one that I’m sure would be better, but I wanted one that could do a variety.

regarding the light, how do I check? All it allows me to do is flip through the messages, and it just says “bulb failure position lamp”

I have learned a slight bit more. So with the dashboard lights on max the fan blows at what feels like the lowest setting consistently and doesn’t cut out, but it’s stuck on the lowest fan speed. However the SECOND I turn the dashboard lights to low the fan blows on max, but then it’ll go intermittent on / off like crazy randomly, etc. For example with the dashboard lights on minimum it will immediately blow at max, and I also regain fan speed control. Also flashing the headlights will make it cut out for a split second in that scenario.

the only consistent thing I can get out of it is to put the dashboard lights on max and just let it blow air at what feels like the lowest setting (even though I have it on max)

Does that sound like a bad blower motor relay / resistor? I’m quite mechanically inclined but with electrical stuff I’m lost.

 

I bit the bullet and went ahead and bought a used OEM resistor off eBay for $40. It has a 6 month warranty. I’m pretty sure that must be what’s bad.

 

Your position lamps are your parking lamps. For position lights the bulb out system usually only cares about the 4 red lights on the rear of the car, 2 incandescent bulbs on each side. But your 2012 has led rear parking lights instead of regular bulbs. On some cars the front parking light bulb - the white bar in the middle of the headlamp - when out will trip the position failure message.

Turn the headlight switch to the middle position to turn the parking lights on by themselves -