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Quick question. On the 2000-2005 Bonnevilles with the n/a 3800 do the cooling fans run on low all the time?
I started my car up this morning to check a squeaky pulley and noticed the cooling fans were on... It was 58*F this morning so I know the engine was cold. And I double checked to make sure the a/c was off. I never really paid attention to see if the fans were on when the engine was cold before.
My PCM was programmed by intense to set the fans at 180* so I figured that is what they should turn on at but I'm not sure...

They should only run when the AC is on or the engine temp is high enough. Stuck relay?

Cool I'm not crazy. I was pretty sure those fans were suppose to be on when the engine was cold. Now how would I tell if the relay is sticking?

When they're running again when they shouldn't, find the relay, and whack it with a ratchet handle. Do the fans turn off? Or swap the high and low speed relays and see what happens. That is, if the 00+ has relays for it like a 92-99 does...

Yea I just played swap the relays... They're were 3 of them. A primary, secondary, and parallel. The primary and secondary I could swap the hvac relay for but the parallel was a different number. Anyways that gave me no luck unfortunately. Thanks for the advise, next time I go out I'll give the parallel relay a few good wacks. When I pulled the parallel both fans did shut off so maybe for what the relay is worth I'll just pick one of those up at the parts store.

The cooling fan circuit is a bit complicated in that there are 3 relays, one cool fan1 relay 37 for the low speed relay (right), cool fan s/p relay 39 which determines of the fans are in series or parallel, and cool fan 2 relay 40 for the left high speed. You can see the black s/p relay 39 has 5 pins instead of 4. When the fans are both on low speed they are connected in series through relay 39 which is not energized. When they are both on high speed relay 39 is energized and the fans run in parallel and relay 39 isolates each fan to its respective relay then to ground.

If one of the wires from the fuse block to the PCM is shorted - the dark green wire from relay 37 to the PCM, both fans will always run on low with the engine cold. A bad PCM can cause the same problem. There is no situation where both fans will run on high with the engine cold unless the PCM is bad,

Assuming one of the 3 relays is stuck closed and the car is cold - If relay 39 is stuck closed then the fans will not operate. If relay 37 is stuck closed then the both fans will run on low. If relay 40 is stuck closed then the left fan will run on high.

So if the fans run on low then relay 37 would be the culprit. But if you swap in another known good relay and the problem persists you are looking at a short somewhere.

As a test, have the codes pulled to see if there may be a pending code for coolant temperature below thermostat regulating temperature. (Or wording similar to that. I think the code is p0128.) If you are running a drilled thermostat, or one lower than the 195, when the weather gets colder, if the PCM doesn't see the expected temperature rise within a specific period, it will set that code. I've found that when that code is set, even as a pending code, the cooling fans will be on when the car is cold, which seems just the opposite of how it should be.

Bobgto65, thank you for that bit of information.
I did swap relays 37 and 40 individually with the relay 33 from the hvac slot. I did notice when I pulled 37 or 40 that one or the other fan would shut off but as soon as I popped another relay in they would continue to run so I assume those are operating properly. And now I understand from your post that the black, 5 pronged, 39 relay would only shut off the fans and it did so when I pulled it.

Archon, thank you also. I am running a 180* t-stat. I have never had and engine light come on yet with the intense PCM yet, but I will still check for a pending code tomorrow at the auto parts store. The t stat is still doing it's job and allowing the coolant to hit 180* The good news is right now in traffic it never rises above 180 lol. So I'll figure this out eventually

If the defrost is on I think they will run regardless as that somehow makes use of the A/C compressor even though its blowing warm air. Try turning all interior climate control functions off and check if they are still running.

Do you have a gauge for the coolant temp? Is that reading properly?

Sometimes as a fail safe if the coolant temp isnt' getting a reading it will throw the fans on.

(but also the defrost setting as said above)

BonnieBoy08 wrote:If the defrost is on I think they will run regardless as that somehow makes use of the A/C compressor even though its blowing warm air. Try turning all interior climate control functions off and check if they are still running.

Yes, defrost runs the AC to dehumidify

toastedoats wrote:

BonnieBoy08 wrote:If the defrost is on I think they will run regardless as that somehow makes use of the A/C compressor even though its blowing warm air. Try turning all interior climate control functions off and check if they are still running.

Yes, defrost runs the AC to dehumidify

Unless it is below a certain temp. Can't remember what temp, but it can be changed in HP tuners.