Radiator Fan stays on

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Tgranted
Posts: 3
Joined: Tue Nov 15, 2011 10:26 am
Car: 2008 Infiniti G35 Sport
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I am having a hard time figuring this issue out.

Car overheats when idling on a warm/hot day.
Fans come on when car starts when cold and stays on.
I replaced the fan control module and fans still comes on when car is cold.
I am tested the radiator fan relay for continuity and it checks out.

I also notice there is no coolant in the reservoir when cold.

What am I missing?
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VStar650CL
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Joined: Thu Nov 12, 2020 1:25 pm
Car: 2013 Nissan Altima 2.5 SL
2004 Nissan Altima 2.5 S

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The fan relay on your ride just provides power to the Fan Controller (FCM). When the fans come on with the key with the A/C off, it either means the FCM has a failure, the PWM driver circuit in the IPDM has a problem, or the ECT sensor has a problem causing the ECM to instruct the IPDM to run the fans. The violet wire into the FCM is the PWM line, it's referenced to 5V with a pullup resistor inside the FCM. The IPDM pulls it to ground with a transistor, 0V is "fan off" and 5V is "max speed". Back-probe the wire and take a voltage measurement when cold, if it's 5V then the fan is doing what it's supposed to do and the problem is elsewhere, probably a bad wire to the IPDM or a blown drive transistor. If it's 0V or 12V then your new Fan Controller is defective. If it's a "middle voltage" then the IPDM or ECT sensor may have a problem causing the fans to run at partial speed all the time, which may be causing your overheats. In that case, let the car get warm and see if the voltage at the Controller rises. If it doesn't then you'll need a scanner with work support to test the fan via software and read the ECT sensor.

Tgranted
Posts: 3
Joined: Tue Nov 15, 2011 10:26 am
Car: 2008 Infiniti G35 Sport
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Thanks VStar.

Now I need to Google those acronyms to know what the heck you're talking about.

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VStar650CL
Technical Expert
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Joined: Thu Nov 12, 2020 1:25 pm
Car: 2013 Nissan Altima 2.5 SL
2004 Nissan Altima 2.5 S

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PWM = Pulse Width Modulation, it's one way an on-off digital circuit can produce a variable voltage.
IPDM = Integrated Power Delivery Module, it's the fuse-covered thing under your hood that isn't a fusebox, it actually has brains in it.
ECT = Engine Coolant Temperature sensor.
ECM = Engine Control Module (your engine computer).

Tgranted
Posts: 3
Joined: Tue Nov 15, 2011 10:26 am
Car: 2008 Infiniti G35 Sport
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Thx VStar.

That's extremely helpful.


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