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Discussion Starter · #1 · (Edited)
So I turned off my car yesterday after I got off work. I was walking away and I noticed the fan was still on. I popped the hood and realized that the coolant overflow was low. So I filled it up and drove around the block one time with the heat on full blast, fans still stayed on. Came home after playing some disc golf with some buddies, fan is still on. Next day the battery is dead. I’m assuming it could be a relay issue, definitely could be a coolant or thermostat issue. Has this happened to anyone?

2018 Black Edition 50k miles
 

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Discussion Starter · #2 ·
Driving around today and still the same problem. I’m going to try and check the relay when I get off.
 

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I would be checking the fans sensor first. The fan switch senses liquid, so if low on coolant it may not close (turn on). Thermostat wouldn't be suspect, either.
I'll guess relay or fan sensor/switch.
 

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I thought the sensor in the bottom/cold radiator tank, and/or the compressor on, signaled the ECU to turn the efans on. If the compressor is off, the cooling system would be virtually empty if the sensor is not sensing liquid in the bottom of the radiator. A properly functioning t-stat does not need to be in liquid to function (open/close).
 

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Modern engine controlls operate with a heat soak safety built in. If one of the engine coolant temp sensors is seeing above a certain temp when the engine is shut off the fans will stay on until the sensor reads below XXX*F.

Look at your temp gauge, is your engine running on the hot side when you shut it off?

The dead battery could just be a side issue, is it the original battery? If so, 3-4 years is about that time that it may need replacing.
 

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Usually, there is a fan “WARNING/CAUTION” sticker under the hood when efans run when the motor is off. Does sound like it may be running a little toasty. A G2 needing added coolant????…..may need to look further to find out why.
 

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So I turned off my car yesterday after I got off work. I was walking away and I noticed the fan was still on. I popped the hood and realized that the coolant overflow was low. So I filled it up and drove around the block one time with the heat on full blast, fans still stayed on. Came home after playing some disc golf with some buddies, fan is still on. Next day the battery is dead. I’m assuming it could be a relay issue, definitely could be a coolant or thermostat issue. Has this happened to anyone?

2018 Black Edition 50k miles
Were the fans running at low speed or high speed?

The fans normally run at low speed when the A/C compressor clutch is energized.

The fans normally run at high speed when the high side A/C pressure or the engine coolant temperature as measured by the ECT2 sensor (the one at the bottom of the radiator) rises above a specific threshold.

The fans normally run only when the ignition is on. Unlike some vehicles in the past, they are not designed to operate after the ignition is turned off. Neither a low coolant level nor thermostat problem should cause the fans to run with the ignition off.

In order for the fans to run at low speed, only the A/C condensor fan relay has to be energized. This relay is energized by the PCM pulling one side of the coil to ground. If the fans continue running on low speed after the ignition is switched off, either the A/C condensor fan relay is sticking, the PCM is faulty, or there is a wiring short to ground.

In order for the fans to run at high speed, three relays would have to be sticking or two outputs on the PCM would have to be faulty or there would have to be multiple wiring issues so this is highly unlikely.

I suspect your fans are running at low speed and that the A/C condensor fan relay is faulty. I'd pull the relay. If the fans stop, I'd check for 12 volts on terminals 3 and 4 of the relay socket. If there is no voltage, the relay is faulty. If there is voltage, either the PCM is faulty or there is a wiring short to ground.
 

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Very nice reply, @zroger73.
Thanks for all the detailed guidance you provide to everyone here.

I wish we could get (more economical) access to technical docs. The subscription model can get pretty spendy over time, but I guess (keeping things in perspective) the daily access fee is much less than an hours labor charge.

I remember when I could order a set of factory service manuals from Helm shortly after each new car purchase. I always thought model-specific Honda service manuals of that quality, at those prices were too good to be true.
 
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