Both cooling fans not working

[cmracing]

Both fans on my 2009 Lucerne won't come on. Being winter, as long as the car is moving it won't overheat, but can't keep going like this.
Both fans and relays are good. Scanner shows water temp got to 223, that's when I shut it off.
I can ground each relay under the hood, they will click, one relay will run one fan, the other relay will run both fans.
So, what controls the ground side of the relay coils?
Did a Google search, found no answers, so here I am, hoping someone on this forum can help me.
We bought this car brand new and plan on keeping it forever, though that 4.6l makes me cringe when it gets hot!

 

[2007LucerneCXL]

There's are posts on the fans question but each vehicle is different on the problem and solution. Assuming that there is a problem, dash temp gauge is above normal or the fans don't turn on with the AC turned on, all 3 underhood relays and fuse check out by testing them (V6 assume V8), fans are jumped directly and run, temperature sensor on engine is operating, no shorts in harness. A scan tool that can command the fans on is useful if available.

Chilton manual online, see link below on the forum go to post #40 for information on how and what is involved to login. It has wiring schematics which can help on chasing the fans sources.

Free Chilton Online Repair Manual

Thanks again!

buickforums.com

 

[cmracing]

Yes, dash gauge higher than normal, ECT on scan tool shows correct temperature, A/C is on, only checked two underhood relays, didn't check a third. If I manually ground two of the fan relays the fans turn on, so unless there is a wiring issue which happened to both of those relays at the same time, I was wondering if the BCM has anything to do with this.
I will see if I can borrow a scan tool which can be used to control each of those fan relays, then I will know if the PCM or BCM has an issue, or somehow two wires both got cut/chewed at the same time.
Thanks for the Chilton link, I will take a look at that also.
This is a Lucerne Super, Northstar engine.

 

[2007LucerneCXL]

Unfortunately if you read those other posts on this issue there doesn't seem to be a common problem it's ranges from a underhood corrosion fuse box to a bad fan connection and everything in between so it's difficult to say what a common item is that is the failure point.
Here's another post, not common but is a good example of troubleshooting on something that wouldn't be even considered as a cause.

2011 Buick Lucerne No A/C or Radiator Fans

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. P0036...

buickforums.com

 

[cmracing]

Yes, that is the post I had found via Google, and this forum. Crazy that an oxygen sensor fuse provides power for those three fan relays under the hood, almost opposite ends of the car!
I have two friends that worked at Buick and Caddy dealerships, I sent them a text to see what they think. They said the PCM controls the ground circuit for those relays, so it's either a couple of bad wires, or a bad PCM....

The fuel pump relay gave me problems years ago, wasn't actually the relay, but the wonderful GM fuse block under the rear seat. My buddies told me they have replaced LOTS of those! I found the correct wires and put my own relay back there, was not about to replace that entire box.

Thanks for the info, going to spend some time reading around here. Have replaced the front struts, got really lucky getting NOS for the magnetic ride suspension, but now I need rears. I have found some conversion kits and may do them instead. The magnetic ride is great, but the cost of replacement parts is crazy.

 

[2007LucerneCXL]

Like that old post shows and others out there, it's not always a straight line and a lot of post from people are looking for the silver bullet part. As soon as I find those magic fix all parts I will list them on the forum LOL. Good luck on getting it resolved.

 

[paul8539]

I had that same problem a while ago also. It was an O2 sensor fuse.

 

[cmracing]

Well, I should have started with the basics. We had the water pump changed a year ago, I did it the first time, I paid someone else to do it the second time. Anyone that has done one of these knows what a chore it is. My Northstar isn't the easy one, I have to remove the manifold that goes between the heads and block to remove the water pump, what a PITA!
Anyway, I used a special vacuum setup that pulls a vacuum on the cooling system and then you fill it.
I am sure the Buick dealer did the same thing.
After messing around with the fan relays for weeks, I checked the coolant level, it was a full gallon LOW!
Either the dealer did not fill it correctly, which I think they did, since this problem recently arose, or I have a leak, which has not shown in the garage. But, could be the wonderful head gaskets..............
I don't smell antifreeze going through the exhaust, and I hope it isn't, but now with the coolant level correct the engine is perfect again. 🙂

 

[2007LucerneCXL]

Thanks for the update and it's another one on the list that may help others.

 

[G-817944]

I had that same problem a while ago also. It was an O2 sensor fuse.

Is there a o2 sensor in rear fuse box