2000 Century: Cooling fans problem

wrongturninwv

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2000 Buick Century
Found 25 amp cooling fan fuse blown in box under hood. Put new 25 amp fuse in and no fans. Changed 3 pin Temp sensor, no fans. Changed 3 fan relays in fuse box under hood, still no fans. When I take plug off to temp sensor while running car both fans run fine. Put plug back on sensor fans turn back off. My AC stopped working a year ago but I don't think that would have any thing to do with the fans. Service engine soon light on far left side of dash is on but I used scanner and pulled no codes. My dash has been crazy for years. Every thing at start up is fine then gas gauge drops to empty and ABS and Trac off lights come on. Need some help here, not ready to junk her yet. thanks
 

Zeroboostbuick

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2018 Regal Sportback - 2010 Yamaha R6 (track bike) Past cars: 92 LeSabre, 98 Regal, 02 GrandPrixGT
Did the fans stop working at about the same time as the AC ??? just wondering because when the AC is ON, the radiator fans should also work (at least 1 of them should). So maybe related, maybe not.

If the wheel hub bearings and the speed sensors within them are good, then the ABS and Trac problem will be with the wiring at the control arm going to the hubs. Here is a video showing the ABS Trac problem, how to diagnose it and fix it.


The gas gauge problem will be with worn out contacts on the fuel level sending unit inside the tank. Recently I read on another thread on this forum about a product called "Techtron Plus ". I think it's a liquid in a bottle you put inside the tank at fill up. But I have no idea on how successful the stuff is. Much easier to try it than buying a new sending unit ( $60 to $100) and swapping with the old one. Fuel pump / sending unit access is from the back seat through the trunk opening, under trunk carpet right by the back seat is a access panel to the fuel pump.

Those Fans not working, but working when temp sensor is unplugged has to be diagnosed by a car magician ( ie... guru with a scope on a rope and other electrical probes ).. Unless you know how to chase down electrical gremlins. Maybe someone who had the same problem will chime in and tell you the fix. But I wouldn't hold my breath.
 

wrongturninwv

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Thanks for the info. I guess it would not hurt car to just run the fans direct as long as I rig it to where they turn off when I turn key off. thanks
 

MelsRegal

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You have a service engine light on but no codes, did you check for a blown fuse for the OBDII port, sometimes it is the cigarette lighter fuse.
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wrongturninwv

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You have a service engine light on but no codes, did you check for a blown fuse for the OBDII port, sometimes it is the cigarette lighter fuse.
You have a service engine light on but no codes, did you check for a blown fuse for the OBDII port, sometimes it is the cigarette lighter fuse.
No I did not. But I will check it out. Just can not see how when I unplug the 3 wire plug to the temp sensor that the temp gauge on the dash still works. Is there another sensor for the gauge ???
 

ceTNury

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No I did not. But I will check it out. Just can not see how when I unplug the 3 wire plug to the temp sensor that the temp gauge on the dash still works. Is there another sensor for the gauge ???
Did you ever get this puzzle worked out? My dash isn't freaked out like yours but my AC and fans seem to have the exact same issue.
 

AshTray900

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not sure about the 2000, but my 96 century and my 99 olds alero both had a poorly placed wire that ran to the side crank sensor and the speed sensor, speed sensor wires were melted, MPH gauge would bounce and transmission wouldn't shift properly sometimes, I pulled mine and just covered the bare wires with a good bit of electric tape and tried to place them away from exhaust manifold, if I'm even back down that way I will professionally repair the harness with replacing the wires, solder, heat shrink, and looms, will make them long enough to get far away from manifold
 

ceTNury

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not sure about the 2000, but my 96 century and my 99 olds alero both had a poorly placed wire that ran to the side crank sensor and the speed sensor, speed sensor wires were melted, MPH gauge would bounce and transmission wouldn't shift properly sometimes, I pulled mine and just covered the bare wires with a good bit of electric tape and tried to place them away from exhaust manifold, if I'm even back down that way I will professionally repair the harness with replacing the wires, solder, heat shrink, and looms, will make them long enough to get far away from manifold
The wife has had some shifting problems(doesn't do it when im driving, making it hard to troubleshoot) so this might explain both issues(fans & shifting). Looks like it's time to pull out the creeper and stands this weekend. Thanks for the info!
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AshTray900

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Did you ever get this puzzle worked out? My dash isn't freaked out like yours but my AC and fans seem to have the exact same issue.
my ac doesn't even turn one of the fans on, the other works fine, the relay to the inactive fan is good, the fan is good, and the harness seems to be good as PCM detects a fault if relay plug is removed in the trigger wires. mine does odd things, the big fan kicks on and keeps the car cool it ranges from 202 (good operating temp) to 220 (seems to be safe for this engine) these readings are by bosch 1300 scantool, the needle changes between 1/4 to 1/2 and back when sitting still in ANY kind of weather, I specifically asked for the 195 and not the 180 thermostat when doing LIM, according to scantool this is right, when moving the needle remains at 1/4 and the scantool reports 200-202. my assumption would be the correct procedure for these fans (on mine a large internal radiator one and a small external condenser one) would be to turn on the small front one whenever the AC is on and whenever the temp bumps say over 205. and activate the large one in higher temps as a supplement and a failsafe. that's just common sense to me.

I have seen differences in temp sending units and where the dial sits. there are three wires so at the least this sensor is sending two signals at most 3, I may go back to the dealer for temp sensor if I'm back in to where I can get to it without worrying about the socket breaking it, I also may just wire the little fan with a dual relay, the stock one (for whatever it does) so the PCM doesn't complain, and then a second one to just run this one all the time when the car key is on.

Some of the newer models may run with dual side by side fans (I think my alero did) this fans had two speeds, slow and fast they may have even had a three prong wire.

on my 96 century I have been all over the motor, that one temp sensor by the thermostat is the only one, I think the 99 with the 3400 was the same way.

These cars seem to be plagued with electrical issues, many can be solved with a tiny eyeglass screwdriver to bend more tension back into the plug and the application of a little dielectric grease.

I'm still at a loss why my little fan wont come on, I think it use to with the compressor, and my AC still blows ice cold. ive gotten a lot of people pointing towards the PCM. but mine was so well kept out of the heat I doubt it would be the issue.

ive been rebuilding electronics from the 30s-90s and even some now when a computerized board that is more expensive than the equipment just burns out due to heat.

ive never torn one up, but from what I gather a PCM is a very rudimentary computer, computer parts go out for one main reason, electrolytic capacitor failure, capacitors fail from heat and improper climate or just manufacturing flaws or cheap construction, the electrolyte dries out in them, capacitor failure can result in voltage regulation failure, and in situations where AC current is present, failure to filter out AC which will fry a chip in a split second. other applications would be poor current quality in smaller situations. this leads me to believe, total PCM failure would (in modern vehicles - OBDII) complete failure to operate. at best it could cause the situation the person above described (everything erratic) but I'm very skeptical of PCM failure being responsible for loss of one function unless the PCM itself was poorly designed and couldn't handle the load on it and burned a trace in the board.

maybe a cold start and triggering the pins of the sending unit plug would rule it out, and you could go from there, I'm thinking of running 1 continuously (the low power one) this will steady my needle in all situations and keep the car right at a good 200 and supplement the AC performance without running the risk of total fan failure (my main fan runs fine).

your case, fans - probably fine, sending unit - maybe, electrical gremlins - likely. trip the fan relay manually to check fan, test relay, check for 12v on signal leads and monitor, if they don't activate when they should think about replacing the temp sender (after 2 parts house ones, I recommend dealer part, also overheat can make these go bad even if they look fine) if that doesn't fix it your stuck figuring out your electrical gremlins or trying to get around them. GM - melted wires and plugs that go bad are rampant
 

ceTNury

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your case, fans - probably fine, sending unit - maybe, electrical gremlins - likely. trip the fan relay manually to check fan, test relay, check for 12v on signal leads and monitor, if they don't activate when they should think about replacing the temp sender (after 2 parts house ones, I recommend dealer part, also overheat can make these go bad even if they look fine) if that doesn't fix it your stuck figuring out your electrical gremlins or trying to get around them. GM - melted wires and plugs that go bad are rampant
When I unplug the sensor by the thermostat both fans kick on. AC stopped last summer, turning it on doesn't do anything for the fan. I need to spend weekend on it, trace the whole circuit, check every connection, sensor and relay in the loop.

15 years in the Az sun are great for the rust, but he'll on the plastics. Brittle connectors all over, any one of them could be broken and causing problems. Fun stuff...
 

AshTray900

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1996 Century Wagon
When I unplug the sensor by the thermostat both fans kick on. AC stopped last summer, turning it on doesn't do anything for the fan. I need to spend weekend on it, trace the whole circuit, check every connection, sensor and relay in the loop.

15 years in the Az sun are great for the rust, but he'll on the plastics. Brittle connectors all over, any one of them could be broken and causing problems. Fun stuff...
Hmm fans kick on when sending unit disconnect, so that circuit presumably good? Car properly cooling without ac? Does ac compressor kick on?

If so on both your system probably is unable to run fans on low power, the newer ones with twin fans had dual speeds. My alero did. Being separate from the compressor as to not cycle with it.

3 prong fans or two?

2 prong, you probably have a failure in the resistance or pulse to the fans
 

ceTNury

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Hmm fans kick on when sending unit disconnect, so that circuit presumably good? Car properly cooling without ac? Does ac compressor kick on?

If so on both your system probably is unable to run fans on low power, the newer ones with twin fans had dual speeds. My alero did. Being separate from the compressor as to not cycle with it.

3 prong fans or two?

2 prong, you probably have a failure in the resistance or pulse to the fans
No compressor activity when I turn the AC on. Cheapie refill gauge shows it's full. But those aren't exactly reliable if there's an actual problem.

3 prong sensor. I need to plug it back in and see if the fan will kick on at 225 (I believe that's the temp they're supposed to). Thermostat is new, just had fresh heads put on after a head gasket went. This problem was going before that(and likely contributed).

Might just do what several have mentioned and put a toggle switch off that sensor for driving in town\traffic.
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AshTray900

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IMO toggle is bad, relay good, relay to cut it on automatically, toggle bad bc youll forget trust me it happens to the best of us

so if the compressor isn't kicking on this is why the fans aren't running at low speed - not an issue with no ac functions

high speed is the issue, now when you say fans kick on when you disconnect the temp sender I assume this is kicking in high gear, high enough you can hear them good like they need to cool the engine down not just rolling around quietly.

this would suggest to me that the temperature sensor either has an open situation as it gets hot, basically it stays low resistance and increases resistance as it gets hot so when you pull the plug you are at max resistance (open circuit) and this turns the fans on as they should (this doesn't naturally make sense to me, I would think its the other way around, but I don't know) if this is correct everything is fine and the portion of the temp sensor controlling the fan is bad. this is likely possible even if the gauge still works, there could be two circuits in that sensor, a switch circuit (like for a classic car with a temperature light and no gauge), and also a variable circuit, this variable circuit would control your gauge and your light in this situation since you don't want the hot light coming on with the fans, the computer would read the variable circuit and decide when its hot enough to trigger the light. the temperature switch would be shorted closed (still doesn't make sense to me as in classic vehicles with the light and only a switch and no variable circuit this would close when hot, however this may just be due to the older cars having no relays or computer on it just needing it as a switch to power the light)

at any rate leave the connector on, probe the wires, my guess is you have a common wire, a variable wire and a switch wire (schematic in Haynes will verify its not using the manifold as a ground etc. set your meter to resistance, put negative terminal on the common one, start the car, set the meter to resistance, watch each of the other wires, one should gradually change resistance, the other would stay in the same state until the car is at a temp the fans should be on (don't let it over heat) if the other never changes replace the sender.

or if you want to avoid all that crap, just replace the sender its not expensive to get a good one and see if it solves the issue, I assume you haven't been changing 5 pin relays around all over the place or rewiring them to change the state, 5 pin relay has three active pins- common, active with no power, and active with power, it just flips a lever like a light switch but off is actually on for one of the pins, the other two control the switch via an electromagnet
 
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