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Noise from back of the car, when car is off


dmk2000
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Last night it happened again.

After coming from work, I parked my car and was walking to the house, when wile passing my wife's Cmax, I heard fainted noise from the back of the car. The same noise as someone here posted video of it. I walked in the house and ask my wife when did she came back. She told me it was over an hour. So I took my volt meter and went outside. Checked 12 V battery voltage and it was 12.5V. Good, battery is not dead. What I did is turned car on and then off. Guess what, noise is gone. This morning car started fine and she went to work. This leads me to believe if I would not take care of this sound, by the morning the 12 V battery would be dead. I incline toward the theory that HVB cooling blower in some cases prevents computer from totally powering car off, and in the same time keeps this blower on until 12 V battery is dead. Based on a HVB pack design, the noise is very likely coming from this cooler blower:

 

cmax-energi-battery-pack.jpg

I know this is a picture of CMAX ENERGY battery pack, but CMAX hybrid also uses this configuration for cooling. 

What do you think? Did anyone with 2014 CMAX seen similar issue?

Edited by dmk2000
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dmk,

 

It has been suggested in the past that the ventilation for the battery coming on and not turning back off might be a problem.  I've wondered if that's an issue, too, as all of the problems I've had occurred when the overnight temperature was within a certain temperature range -  low 50's (which I think is what it was last night in NJ)... but not every time it's in that range.  As far as I know, nobody has determined that for certain, and there are no TSBs from Ford to that effect... yet.  The thing that doesn't make sense to me is: if that were really the problem, it would probably be a software issue, and would apply to all C-Maxes, not just a few.  So who knows.

 

I'd recommend an experiment - if you notice it again, leave it alone and see if it's dead in the morning.  Not a great solution, but it would definitely be an excellent clue.

 

I'm curious - how did you test the 12V voltage?  Did you disconnect the battery, or did you test it live?  If it was live, it's likely that you weren't actually testing the battery voltage, since the car woke up when you opened it so there would've been a current draw... and I believe the DC-to-DC converter would've immediately started charging if it were low (although I'm not certain of this).

 

Anyway, great thought, and I'm curious to hear any additional info from others.

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Interesting theory but nope. I hear always hear the fan on as its hot here in LA and I always use EV+ to finish on the top of the hill where my garage is. Plus I probably EV more than anyone here as well so the batts is more used than ICE. Start it the next day, fine...

 

Jus - you hear the battery ventilation fan on well over an hour after you've powered off the car?  I've heard mine on, but usually only for a few minutes after I leave the car - not hours later...

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Jus - you hear the battery ventilation fan on well over an hour after you've powered off the car?  I've heard mine on, but usually only for a few minutes after I leave the car - not hours later...

I will check, I recall its in minutes and not hours but I can't be specific, I never bothered to time it - but I will today...

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Hello everyone.

Well, it could be a fuel system as well, that said, why would it be on for over an hour? Same applied to cooling fan. I would expect it to be done withing minutes. I am thinking along these lines, if there is a reason to run some modules in a car after turned off procedure, it could be a high temperature of HVP, or fuel line pressure check, then by turning car on and off again should still keep these system running until conditions are right for turning them off. In my case, after "rebooting car" these activities are no longer present. If HVB cells are hot, then fan would still run till temperature is withing a normal range. Same applies to pressure maintenance on the closed system, I would expect it to resume as well until test is done. I was tempted to let it run till morning, but since I do not have a "backup car", and both of us need to be at the place of work in the morning, I had to stop it. As far as battery test, I did it using connection points in engine bay.  

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dmk2000:

 

You could have a bad fan relay staying on. It's not uncommon for relays to fail and cause

the load to remain active until power is cycled on. I don't have that relay location, but if you can find it's

location and next time you hear that fan running after it should have turned off, you could tap on the relay

without cycling the key and see if the fan shuts down. This would verify a stuck relay.

Edited by drdiesel1
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dmk2000:

 

You could have a bad fan relay staying on. It's not uncommon for relays to fail and cause

the load to remain active until power is cycled on. I don't have that relay location, but if you can find it's

location and next time you hear that fan running after it should have turned off, you could tap on the relay

without cycling the key and see if the fan shuts down. This would verify a stuck relay.

Hi drdiesel1.

Sound like a possible cause. Will try to find it.  

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