2011 Buick Lucerne No A/C or Radiator Fans


New member
Thread starter #1
Hello and thank you for reading first of all. Me and my Father in law have an issue we just can't seem to figure out. After quite some testing we're still in the dark here.

There are codes showing the cooling fan relay is bad. Currently the code readout from the OBD is as following.


Now, so far we've tested and even swapped every relay that has to do with the A/C and the Cooling fans to no avail. Forcing the relay for the A/C will engage the unit and we do get cold air but without control it could overheat and damage the system. Both cooling fans work perfectly when powered externally. However, we have absolutely no signal for the relays to engage either the A/C or Cooling fans to their respective relay; even when the engine hits nearly 230F.

We've tried swapping the temperature sending unit, tried resistance shorting it, and when it's off or shorted the display will tell you "Engine HOT, A/C OFF" in the dash. When everything is plugged in; nothing is displayed about an issue. I've read just about everything google has to offer on the issue to no avail. I have heard rumors of fuse box issues with the Lucerne but most of those posts were 2006-2008 model uses showing issues. There's even a few posts on this forum about similar issues. I'm not totally convinced the issue is related at all. I know the O2 sensor is bad, but we're eliminating the worst problem first. We have to wire the cooling fans on a switch to even use the car for the moment. Ambient lately has allowed normal driving to keep the engine in safe operating range as the car doesn't see a lot of stop/idle times. Come in a few months however, that may become an issue as ambient will be rising.

We've checked every fuse, every relay, and even tested the wiring for contact. There's just no signal to the relays at all! So they can't engage, which we've tested them and every one works properly. What would cause this issue? Is it possible the fuse box is problematic and we'll have to fix that?

Thank you ahead of time for any assistance! Other things to note. Car has 135k miles, daily driven, no other known issues lately. The O2 sensor has been throwing a code since the beginning of winter and 99% is most likely non related. We planned to replace in spring until this issue popped up about a month ago.


Full Member
Buick Ownership
Ex-Lucerne Owner, Now loving my Chrysler 300.
We had no AC (clutch would not engage) and no fans on our 06. Turned out to be rust on the connections under the fuse box in the engine compartment. We did not have any OBD codes.


New member
Thread starter #3
Thank you polarzak. We're planning to pull the fuse box this weekend to check the wiring under it. It's throwing a code for the cooling fan, so I know many ECU's will refuse to engage the A/C when that is triggered since usually they are used to cool the A/C's panel as well as it is in the 2011 Lucerne we're working on. I'm guessing that's the underlying issue with the A/C. So, when we pull the fuse box out this weekend we'll check the connections under there for possible shorts and the like. The car hasn't even been in service for 6 years. It was a year end buy from the original owner in August of 2012 if I remember correctly according to the Carfax. Funny thing is there is hardly any rust anywhere aside from the rotors we just swapped out on it. It's been well taken care of as well.

This project has turned into that ghost hunt that is for sure. I'm really not looking forward to cutting open the wiring harness' if there's a bad wire somewhere. However, it wouldn't be the first domestic car I've had to splice into like that; just not one this "young".
Buick Ownership
Ex-Lucerne Owner, Now loving my Chrysler 300.
Ours had (sold it last year) no rust. In fact it was almost in showroom condition as it was rust proofed every year since I bought it new. Even underneath was still shiny/painted if one were to wipe of the rust proofing spray. However, underneath that engine fuse box was a rusted mess. Good luck. Hope it is an easy fix for you.
Buick Ownership
Regal GS 2017
did you go through all the cause for the P0480?
Faulty fan control relay
Fan control relay harness is open or shorted
Circuit electrical connections poor
Faulty cooling fan
Faulty coolant temperature sensor
Fan cooling fan harness is open or shorted
Cooling fan circuit poor electrical connection
Intake air temperature (IAT) failure
A/C selector switch
A/C refrigerant pressure sensor
Vehicle speed sensor (VSS)
P0480 Cooling Fan Relay 1 Control Circuit
Thread starter #6
All of the relays are working as designed. Tested both manually and with another vehicle that uses the same (Chevrolet Truck)
The fan both work when powered externally and within the fuse box manually.
Checked and rechecked all connections; everything works properly and no unusual wear/corrosion
Coolant sensor replaced, twice
The harness is showing resistance between the fuse panel and the connector, no signs of a short with power. (There's never power into them unless forced though)
Intake temperature is reading nominal and correct, though I could try replacing but seems a moot point.
The A/C was tested and deemed operable at the end of last summer. We were going to have it recharged however the mechanic we use for A/C said everything looked great. (May have him look at the system at a later date)
Speed sensor; not sure what that would have to do with the issue, but everything seems nominal in the readings from the OBD, nothing unusual reporting there.

I'm honestly wondering if the panel isn't triggering because the underside of the fuse box itself as was suggested earlier. Usually troubleshooting and fixing vehicles isn't a problem for us. If it's a repair we don't feel we could manage (or have the time to do) we take it to our mechanic. However; even he was at a loss after a half hour (off the clock) exam for us. He's pointed at the wiring as well and gave us some ideas to go on. Hence, the reasoning of looking further into the wiring. We'll be pulling the fuse box and testing the wiring across this weekend. Hoping I find good news under there and it's easily remedied. If not, wild goose chase is on.
Thread starter #7
So an update for you.

This weekend we tore into the car pretty hard. We've narrowed it down to the PCM or the wiring going from the fuse box to the PCM. The fuse box looks rather healthy with very little rust/corrosion on the bottom. We're able to force power the relays and control the A/C. However, forcing one of the three fan relays causes both fans to engage which off this relay should only be FAN1. It's weird as well. we're getting power into the relay from the output of the relay. It's coming in where it should be going out to the fan. We've called our local mechanic (only one we use locally) and he's got the same idea as us. He can usually get us deals on parts so we're going to run it to his shop and using his tools we'll be able to trace the wiring and find exactly if and how many wires may be faulting out. If it's too bad he'll see what we can do in getting replacement wiring for it. I have a feeling that maybe something did some damage to the wiring as it travels under the side of the transmission. About a year ago the car did run over a childs toy at about 60mph when the toy flew out of the back of a pickup. (Strap your crap in people). It's possible something hurt the wiring and it's only really starting to corrode and short out now. However, getting a good visual under there is hard. It does feel like the plastic tube is damaged under the transmission though. We're hoping it's not bad; but if we have to drop a few hundred into a new harness to get everything working we will. The other possibility is that the PCM is malfunctioning itself. We've pulled it out, cleaned all the terminals (which didn't need it), and slapped it back together. After all the work we did yesterday we took it for a drive and the temperature broke 210F and still isn't actuating the A/C at all with absolutely no fans.

We'll be at the mechanics shop a couple afternoons this week using a bit more advanced tools to see what we can find. It's nice having a mechanic that let's us use their tools/garage in their off times. I'll update when we find the specific problem however we're pretty sure it's wiring or PCM itself that is faulting right now.
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