rad fan staying on after engine shut off, even in cold weather

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dlb
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rad fan staying on after engine shut off, even in cold weather

Post by dlb » Mon Oct 08, 2018 3:50 pm

The radiator fan in my wife's 2003 Hyundai Accent is sometimes staying on after the engine shuts off. It started doing this in the summer when it was really hot out so I thought it was normal then. But now it's about 10* celsius out and it's still doing it. The car runs fine, temperature is always perfect, no other symptoms. My guess is the coolant temp switch but I'm not sure how to test it, and I wanted to bounce the idea around with some smart gents before I go replacing anything. Thanks gang.

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splatterdog
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Re: rad fan staying on after engine shut off, even in cold weather

Post by splatterdog » Mon Oct 08, 2018 4:17 pm

Scanned it? Are fans commanded on? Maybe try some swaptronics with another relay if not. Temp sensor resistance spec is 2310-2590 ohms at 68f, 146.9-147.3 at 230f

Worst case is the ecm is commanding it on when not needed. Fan system always has power. Maybe see if the ac switch affects it too.

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dlb
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Re: rad fan staying on after engine shut off, even in cold weather

Post by dlb » Tue Oct 09, 2018 12:46 pm

Funny you mention scanning it. The fan problem started months ago but the CEL came on just a few days ago. So yesterday, I finally jumped into the 21st century and bought a code reader. I hooked it up this morning and it says the intake air temp sensor is the cause of the CEL. So I imagine the fan problem and the CEL are related. I'll replace that sensor and see what happens.

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splatterdog
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Re: rad fan staying on after engine shut off, even in cold weather

Post by splatterdog » Tue Oct 09, 2018 2:30 pm

Well maybe, but I haven't ever seen a connection between the ats and the fan, but I certainly haven't seen everything. Does your code reader show fan command? That is kind of outside what most cheap code readers can do. How about ohms thru the coolant temp sensor? If your code reader does data, ats and cts should be very nearly identical when cool.

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dlb
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Re: rad fan staying on after engine shut off, even in cold weather

Post by dlb » Tue Oct 09, 2018 9:08 pm

Erp, I'm dumb. You can tell I haven't been working on cars much in the last several years. I was thinking the temp would tell the fan when to turn on and off but yeah, of course that wouldn't be determined by IAT.

I'm going to mess around with the code reader and run some other tests tomorrow and see what I find. Wish me luck.

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Re: rad fan staying on after engine shut off, even in cold weather

Post by keith » Thu Oct 11, 2018 8:53 am

In most vehicle today, if the fan is running when you shut down the engine, it will continue to run for about 10 minutes. It's based on a timer and not temperature. If the fan is coming on after shutdown, then either the coolant temp sensor is going bad or you actually have an overheating issue and you need to get the cooling system checked out.

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