replaced cooling fans and they wont turn on,


Asked by Sep 11, 2014 at 03:28 PM about the 2006 Buick Lucerne V8 CXL FWD

Question type: Maintenance & Repair

radiator fan went out on way home from work, replaced fans and they wont turn on.

11 Answers


Probably was nothing wrong with the radiator fan(s). Usually it's either a blown fuse or a relay that has gone bad. Oddos of both fans dying at the same time are unlikely. Look on the fuse block and see if there is a relay marked "cooling" and temporarily bypass that to see if they come one. If not, it could also be the temperature sensor is out because the sensor tells the fan that "it's hot in here, can you give me some air?"

1 people found this helpful.

The car has power to both cooling fan1 and cooling fan2 relay's under the hood. I jumped the relay terminal 87 to 30 to manually turn them on and still nothing. I pulled the power plug from the motors and there getting no power at all. I don't think it's the coolant temp sensor because the gauge on the dash board still works and I was told there is only one temp sensor in this car. I've checked all cooling fan related fuses and all appear to be good. I'm lost as to what it could be. Maybe some fried wiring somewhere?

2 people found this helpful.

I discovered a third relay for the cooling fans. I jumped that relay plus the cooling fan 1 relay and the fan kicked on but if I put the relay's back in I get nothing. I tried swapping relay's around with known good one's but still nothing.

2 people found this helpful.

do you know were it is at? coolant temp sensor

6 people found this helpful.

coolant temp sensor under egr valve. replaced tell you Monday how it goes.

2 people found this helpful.

coolant fans still wont turn on, fuses are good relays are good. any other suggestion?

7 people found this helpful.

Plese let me know if you get this problem solved.i also have this issue and I am problem shooting the wiring.

1 people found this helpful.

I have the same problem too. Had a specialist check it out he said it was the fuse box. Got one from junk yard still not working. The specialist said it could be common and to find another fuse box.


We're having the same issue with a 2011 Buick Lucerne. So far, we've eliminted many potential issues. I doubt a fuse box would cause the problems and we have working fans, as they work when powered. There is resistance across the leads so the wires are intact to their respective relays. All the relays have been tested and working as they should. So, this problem also has us concerned as the AC refuses to engage unless forced by shorting the relay pins to engage the AC. It does kick on and work properly when shorted but isn't controlled which would eventually cause an overheat/failure of the compressor or other components. All points lead to the temperature sending unit; which has been replaced twice just incase of faulty replacement. We're currently in the stages of tracing down the wiring harness to see if there's an issue somewhere along those wires. We've have plenty of wiring issues with previous GM models so we're getting down to that probably being the problem. I'm pointing my finger at the wiring from the sending unit somewhere causing an erroneous reading. I am certain the sensor uses some type of resistance reading to report the temperature of the coolant so all leads are pointing there. I'll try to update next week after we tear into the wiring. We're currently running the car with no AC and one of the radiator fans on a switch in the cabin to keep from overheating.


So quick update; This morning we idled the car in the garage for 22 minutes. The ECU is reading correct temperatures (at least near right) as we ran a contact gauge on the radiator. We gave it +-10F for temperature difference in the radiator and it stayed well within that range up to 230F when we forced the fans on to cool it. So if the ECU is reading temperature correctly; and according to what we've found, the temperature sending unit is pretty much eliminated as a problem. So; the wiring there should be fine though we're still going to trace it out. The car needs to be used during the week however it still has no AC and no automatic cooling fans. So we have a single fan on the switch in the cabin which keeps the water temps in the nominal range for now. When it starts hitting 90F+, that may be a different story. Something to note. When disconnected or shorted down, the temperature sending unit flags the ECU which displays in the dash as an "Engine HOT! A/C OFF" message. Though this throws no codes via the OBDII, we're still confused why the AC and Fans aren't operable. Just for giggles we tried forcing the relay's this morning and they all function properly but we're literally getting no signal current to the main relay which seems to be jumping the two relays to control the fans no matter what the circumstance is. So, as I said in my previous post; we're going to do some wire tracing this coming weekend when the car isn't needed in service and I'll update. Figured we'd try to get something done this morning in the garage for Mom (mostly hoping the A/C could work) since it's Mothers Day.


Update. So we've traveled the wiring from the PCM to the fuse box. There's an issue somewhere between the relays and the PCM in the wiring. We're going to take it to our local mechanic as he said he'll help us track down the actual issue. The fuse box is fine, the connections are fine from the relay to the cooling fans and AC unit. Our mechanic has the same idea as we do; there's a short/cross/broken spot in the wiring harness from the PCM to the fuse box or the PCM itself is malfunctioning. Since we're able to reproduce the same codes over and over it seems to be the only option. We're getting power in the wrong places from the FAN2 relay (powering into the coil of the relay instead of powering the actuator circuit). From what the mechanic says; the wiring harness replacement will be pretty costly for stock but he's going to call painless and see if we can get one for cheaper. (not a plug, but love painless replacements as they are the only I've had plug and play replacements from). So, if it's a serious problem in the wiring we'll just be replacing the entire harness. We're worried possibly corrosion inside the harness caused this issue. We're able to actuate everything via the fuse box. A/C works, Fans work, and even forcing two of the four associated relays will cause the fans and A/C to work. It's definitely PCM or Wiring to it. Bottom of fuse box looks pretty good, no visible rust/corrosion to cause the issue. Maybe our problem is just one not many if any at all will run into. But I hope my posts help someone out there!

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