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Discussion Starter #1
OK `let me start from the beginnign. My da bought his car about 4months ago and after two weeks the lower radiator hose blew off. It still had the factory clamp on it. But my dad not knowing drove the car home and it got so hot it cut off. I fixed bled the system and he was fine. A few weeks later his guage quit workin in the dash no big deal. Flash foward i got his car from the body shop went to my local auto part store and put a new sensor in for the guage. The car is going pegging the gauge and a code p1641 is coming up the fans will not come on unless i turn on the a/c or disconnect the the switch at the pump. I also had my car next to his and swapped my relays to his car no change. I did a search and i saw a thread about changing the harness which. would the harness be bad even if the fans were still coming on. I also changed the sensor on his water pump.
 

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For the P1641, check the condition of the plug the relay goes into. These have been known to fry.

Do both fans come on when you disconnect the ECT sensor with the engine running? If not, which does not?
 

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Yea both fans come on when you unplug it that's what strange to me I checked the relays and when the switch is disconnected I pulled the relays and they quit spinning. What exactly makes the fan come on at low temps to prevent overheating
 

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PCM controls the fans based on A/C head pressure and temp from the ECT sensor.

Primary (passenger) fan: 225F or pretty much whenever the AC compressor is running.

Secondary (driver) fan: 232F or high A/C pressure.
 

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Discussion Starter #5
ok now thats intersting my car the drivers side always comes on first. So if it not coming on how could i tell if the ecm has a issue. i cant really find info on this code
 

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Discussion Starter #7
sorry cletus im probably confusing you i switched cars. My Car the driver side fan comes on first dont know why. The original car i was referring to was my dads car when i unplug the switch on water pump they both come on now exactly which one comes on first like that im not sure but they both come on i even replaced. Correct me if im wrong the sensor inn the head is for the guage only and the sensor in the water pump is for the computer. Im going to try to get his car to my job and hook up the scanner so i can see what the computer temp is reading.
 

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[SNIP]

Correct me if im wrong the sensor inn the head is for the guage only and the sensor in the water pump is for the computer.
That's correct.
 

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OK, we need to deal with these cars seperately. Your switching back and forth between cars and its confusing. On YOUR car, do both fans come on if you unplug the ECT sensor with the engine running?
 

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Discussion Starter #10
yeah i was speaking out loud sorry. Im not worried about my car its not over heating. Its my dads with the prolblem When i unplug his switch both fans come on but the p1641 code is on i switched out both sensors and relays in the car i also put new fuses just to know when he turns on a/c the pass fan comes on and it wont over heat i havent ran it long enuf to ever see if the sec fan come on with the ac. the check engine light is on no matter what i do if i just let it sit there and idle normally with the sensors plugged in it wil go to the red and the overheat light will come on . Its a strange im thinking the ecm may hav a issue and thanks for the help didnt mean to confuse you
 

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That is odd. I've never seen where this DTC would be set and the fan would work with the A/C on but not when the engine coolant temp threshold is passed. Is this the only code the PCM is storing?
 

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Discussion Starter #12
Yes if i clear it with my cheaper scan tool it will stay out until what seems like it is trying to send a signal to make fans come on but not workin then it sets again. I was wondering if the harness at the fans had seperate wires for the ecm and a/c signals Im going to take it to work this week and hook up to my solus to make sure it is getting a proper temp reading to the fan
 

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well i have good news i took the car to work today and put it on our solus scanner and found out that the new sensor for the guage was bad (thanks oreilly) the car was not overheating i went and got another sensor put it in and all seems well the code also has not come back which i find strange. Just wanted to say thanks to cletus and junior for there help
 
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