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2G Radiator fans only coming on when I disconnect the temp sensor

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952g63t

10+ Year Contributor
401
34
Mar 19, 2012
Summit Point, West_Virginia
Replaced the temp sensor, same.

Checked the continuity of the clip that connects to the sensor. Both leads are fine.

It's possible that they come on when it gets VERY hot, but I cannot confirm this.

When the car is running, I disconnect the temp sensor clip and they kick on like they would normally.

Could it be my ECU? Or, could it be a relay?

Thanks,
 
I believe I have solved this issue. I am trying to locate the part locally, but it looks like I'll have to wait to get it shipped.

You would never guess what it was, well at least I didn't realize it until I was researching other parts.

Long story short I was using a 2-wire version of the temperature sender rather than the radiator fan switch. Honest mistake, the damn things look EXACTLY alike.

What I don't get is how it was working when it did. The only thing I can come up with was because my alternator was shot it wasn't producing normal voltage which allowed the sensor to limp along until I swapped my alt the first time. Which is around the same time when the fans stopped working. Or, the leads inside the plastic clip housing were not contacting correctly/intermittently.

If I have to order the part I should know the results sometime this week. :pray:
 
Last edited:
Nope. Completely wrong part. Part is not a switch.

Going to try and replace the water pump this weekend and take apart the t-housing to inspect and clean along with my heater core.


:banghead::banghead::banghead::banghead::banghead::banghead::banghead:
 
At this point I'd rig up a potentiometer to work in the CTS harness. With the key on, make the fans turn on/off with the potentiometer. It's the exact same concept as the CTS itself. Measure the resistance across the potentiometer, if it's way off spec then you have an issue back towards the ECU. If it's dead on, then you know you have a flakey CTS and I'd check it the way the FSM says to do it and put it in hot water with a thermometer and check the resistance at the proper temps. Just because you saw it change in your hand at 98* doesn't mean it's the right resistance at 190*.
 
At this point I'd rig up a potentiometer to work in the CTS harness. With the key on, make the fans turn on/off with the potentiometer. It's the exact same concept as the CTS itself. Measure the resistance across the potentiometer, if it's way off spec then you have an issue back towards the ECU. If it's dead on, then you know you have a flakey CTS and I'd check it the way the FSM says to do it and put it in hot water with a thermometer and check the resistance at the proper temps. Just because you saw it change in your hand at 98* doesn't mean it's the right resistance at 190*.

I don't have a potentiometer atm.
Resistance tests:

1.92 on or about room temp
.950 after heating it up in close to boiling water

connector tests w/ignition on:
4.66 - 4.71 volts (used 2 meters)

Is it normal for the metal connectors inside the clip housing to move at all? I just noticed a wire that goes into the clip would move slightly in and out of the housing.
 
Well, it was rather specific in the book. At 176*F you should see about .26-.36. I'd bet bad luck on the sensor. I'd drop a thermometer in there just to be safe on that call.
 
Well, it was rather specific in the book. At 176*F you should see about .26-.36. I'd bet bad luck on the sensor. I'd drop a thermometer in there just to be safe on that call.

I use my a/c button (a/c is deleted in my car) whenever i'm road racing to keep both fans on, but it seems like one of the new parts you got was a lemon. Hopefully you can exchange the sensor for another and that can fix this problem if not I suggest rigging up your own button to turn the fans on. :thumb:
 
im kinda having the same issue.. start the car cold.. fans aren't on I can turn them on and off with link.. i can unplug the ECT fans come on... my issue is that my external aftermarket temp sensor isnt showing what the temp shows in link anymore... It just started one day out of the blue.. I was setting my ISCposition fans come on cools down fans turned off... a few days later I went to tweak the ISCposition fans came on and never turned off... I have my link set at 216 with a 10 offset.. so usually about 200 203 fans come on and they turn off and it would show 193-196.. WELL, out of the blue fans came on and didnt turn off... I have replaced the rad because i had a small leak and also replaced 2 thermostats fans will not shut off... I did at one time see it drop to 196 when the fans should have turned off but they stayed on.. with them staying on the temp just kept going up..

Any suggestions? think it could be the switch that once the fans turn on at temp it just doesnt know when it cools off to keep them on so with that its not cooling as normal so temp rises?
 
Just my 2 cents.

I wouldn't count on the stock temp gauge to be accurate. You need to hook up a reader and get real time numbers on your coolant temp.

Also, MAKE SURE your have NO AIR in the system. Sounds simple, but i've dealt with a problem like this in the past. Stupid headache.
 
I had the same problem with my chevy before. It looks most definitely like a ECU problem. The wirings were grounded so I had it reprogrammed at the casa.
 
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