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Premium Member
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594 Posts
Discussion Starter #1
Hi all,

OK woke up to a flat battery this morning. Car not used for only 8 days but very flat this morning. I have an hr commute to work so it's not down to short trips, etc and the battery doesn’t look that old.

Just checked that AC Relay and it's rattling so do you guys think this might be the cause and the start of bigger issues? Air con working fine so not sure myself.

I'm going to change the relay regardless as it shouldn't rattle for peace of mind. After jumping the car and driving to work and back battery is sat at 12.85volts and goes up to 14v under load so all seems ok now.

Is the car OK to drive without said relay until I can source a new one? Just a loss of air con or could I do further damage?

Any guidance from those in the know greatly appreciated.

Cheers
 

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Super Moderator
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7,124 Posts
you have a non standard radio, do you have an amp hooked up to it?

Also have you cleaned your battery lately?
You can have a voltage leak just due to the dirt on the battery(no joke)
 

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Premium Member
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594 Posts
Discussion Starter #8
Hi no amp just a replacement head unit and no i haven't cleaned the battery. By this I assume you mean the terminals lol.
 

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Bye bye Honda...
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5,864 Posts
you have a non standard radio, do you have an amp hooked up to it?

Also have you cleaned your battery lately?
You can have a voltage leak just due to the dirt on the battery(no joke)
I'm really interested in your explanation for this!
 

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Premium Member
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594 Posts
Discussion Starter #11
Demonstrated in the following video.

Thanks for this. Battery looks fairly new as previously stated, tried the test and it's drawing no volts as a result of being dirty. I've given it a clean anyway prevention better than cure and all that,.

Picking new AC relay up from Honda MK tomorrow, they hold them in stock so that tells you something
 

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Bye bye Honda...
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5,864 Posts
In practical terms, that YT clip is an exaggeration. What's being seen there (using a very sensitive meter) is a fantastically small leakage current (battery drain/leakage being measured in amps and NOT volts as he suggests) which is insignificant compared to the normal 'parasitic' drain caused by various vehicle circuits (plus reverse leakage back into the alternator).

And the first test he performed early on (checking the volt-drop between each post and its connection, to show up any resistance) should be performed under relatively high load conditions (e.g. with headlights on) to highlight any resistance present.

I think the OP needs to undertake a proper parasitic drain test by pulling fuses one at a time and then measuring the leakage current using an ammeter/multimeter across the empty fuse receptacle to find out which circuit has developed the excessive drain.

If the car has a HFT, then my money's on that!

EDIT - just seen you've decided it's the relay. This would have been easy to prove by simply removing the relay and seeing if the problem then went away...
 

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Premium Member
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Discussion Starter #13
Haven't decided it's the relay I'm changing it regardless as this failed on my friends wife civic resulting in hundreds of pounds of damage as the ac compressor failed, new battery, etc and the initial symptoms were an unexplained flat battery. So once the relay has been changed if the problem persists I'll do the necessary parasitic draw tests etc.

I was always going to change this relay based on my friends experience and the many similar stories online. Also the fact my local dealer holds them in stock suggests they are a common failure. Also the upgraded part suggests the same.
 

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Premium Member
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594 Posts
Discussion Starter #14
New relay collected today and fitted. Dealer confirmed the relay should NOT rattle. There is definitely something loose in there and needed to be replaced. Whether it's the cause of the battery drain time will tell.
 

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Clutch pedal guru
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5,127 Posts
It will be the resistor that's loose causing the rattle.
 

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Premium Member
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594 Posts
Discussion Starter #16
It sounds as if there is something which has come adrift in there. I might open it up and see.
 

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Premium Member
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594 Posts
Discussion Starter #17
Just to update the thread I've had no more flat battery issues since swapping out the relay so fingers crossed it was the cause of the initial drain.
 

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Premium Member
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96 Posts
Good to hear you got it sorted, what is the part number needed to replace the relay? I'm having flat battery issues as well and I'm trying to narrow it down. Already disconnected the HFT and although the car hasn't gone flat since, I still don't trust it.

I've just pulled the relay (it's an OMRON one) and it rattles inside. Cheers :)
 

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Premium Member
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594 Posts
Discussion Starter #19
Hi the part number on my invoice is H39794SDAA05 and was £23.57 Inc VAT. If your old OMRON one is rattling it probably should be changed. Fingers crossed it fixes your issue.
 
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