Hello, have a 2012 Volvo S80 with 182K miles that I just bought. I made a post about this earlier and was told to replace the blower motor resistor, so I did, but it didn’t fix it.

The issue is that my fan speed is not functioning correctly. I believe the main issue stems from my dashboard light control, it literally directly effects my blower motor fan speed. If I turn the dash lights incrementally down, my fan speed goes incrementally up, if I turn the dash lights up, my fan speed goes down. It’s literally like my dash light control is the control for my fan speed but in reverse. My ACTUAL fan speed control *only* works like normal if I have the dash lights on the lowest setting, if not than I have no control over the fan speed, it just stays at the minimum speed.

Also, currently my dash light control is not effecting my actual dash lights (it’s stuck on max brightness), but in the past it has, it seems inconsistent or like there’s a short or something. When it‘s working correctly to change my dash lights and I have them on the highest setting my fan speed symptoms are very similar, however in that scenario with the dash lights on high my fan will instead just go crazy flipping from max fan speed to minimum to maximum continuously & sporadically, so I always just keep the dash lights on minimum all the time.

Lastly, if I park the car and leave the headlight switch in the middle position (is that the auto position?) the tail lights stay on. I have to move it’s position to the left.

One last thing, when I bought this car there was a spare climate control dash / unit in the trunk, but it had the heated seats buttons and mine doesn’t. I checked the label on the wires to my seats and they say “Volvo seats W memory & W heat” so I’m assuming I have heated seats and that other climate control unit is the original one to the car. I tried plugging that one in and it doesn’t work at all. I’m assuming the climate unit is not the problem though because it functions perfectly fine (assuming you have the dash lights on minimum)

My theory is that the headlight control module is shorting out and causing my fan speed issue, but I don’t even know how the two are related.

I did scan the car and I do have a ton of codes. I’ll list the ones that to me seem related.

B105A11 - cabin temperature sensor fan electrical short to ground

B105A96 - cabin temperature sensor fan, component failure, component internalfailure

B105A11 - Cabin temperature sensor fan, general electrical failures, circuit short to ground

B108387 - intermittent fault, recirculation damper motor, bus signal / message failures, missing message

B108687 - air distribution damper motor, bus signal / message failure. Missing message

B108387 - recirculation damper motor, bus signal failure, message failure, missing message

B108187 - Left temperature damper intermittent fault

B108287 - right recirculation damper motor, bud signal message failure / missing message

B108587 - intermittent fault, defroster damper motor, bus signal / message failure, missing message

B108687 - Air distribution damper motor, signal message failure / no signal

B10874A - Lin bus A, system internal failures, incorrect component installed

B108788 - Lin bus A, bus signal / message failures, bus off.

B10884A - Lin bus B, system interns failures, incorrect component

B10888 - intermittent fault, Lin bus B / signal message failure, bus off

B10B913 - Blower control, General Electric failures, circuit open

U200223 - Switch, general signal failures, signal stuck low


for code B10874A, it says incorrect component installed, I’m assuming this means the prior guy installed the wrong type of climate unit? I mean it all works, I just don’t have heated seats.


*** this last code might relate to my dash light switch?

B113087 - intermittent fault, light switch module, bus signal message failures. Missing messages.