ML400 relay clikcing - what does this relay do?
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Member
Joined: Apr 2012
Posts: 80
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2012 ML350
ML400 relay clikcing - what does this relay do?
I noticed a near constant clicking sound coming from the main fuse relay box in the engine when the engine is off.
The relay that is clicking (every few seconds) is the light grey HELLA 4RA 007 793-10
I don't know what this relay does, but I noticed that when it clicks once, my voltmeter shows a drop in battery voltage (engine is off).
As soon as the relay clicks again, the voltage starts to rise back up.
Can anyone explain what is going on? Is this normal? The car seems to run fine, but I never heard this before.
Thanks
The relay that is clicking (every few seconds) is the light grey HELLA 4RA 007 793-10
I don't know what this relay does, but I noticed that when it clicks once, my voltmeter shows a drop in battery voltage (engine is off).
As soon as the relay clicks again, the voltage starts to rise back up.
Can anyone explain what is going on? Is this normal? The car seems to run fine, but I never heard this before.
Thanks
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Joined: Mar 2004
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From: Boston, MA
'14 ML350, '13 C220 CDI, '07 C280, '98 ML320
I think it's an accessory relay. Disconnect all accessories, if any, including radar detector, cigarette lighter, etc. See if you see any difference after that.
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From: Montreal/Cape Coral FL
2012 X6 35i Sport, 2013 ML 350 BT, 2019 4Runner TRD Pro, 2020 CRV-AWD
Seeing as you didn't show where you're from in your sig, is it possible you're in a snow-belt state/province? If so, check all your grounds. You cannot believe what a bad ground will do to a DC circuit.
Thread Starter
Member
Joined: Apr 2012
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2012 ML350
Thread Starter
Member
Joined: Apr 2012
Posts: 80
Likes: 7
2012 ML350
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From: The Great White North
W204 C63 Coupe, W166 ML350 BlueTEC, 928GT, Taycan GTS Sport Turismo, C5 Z06 & IS300 race cars
It could be something as simple and normal as the AC dryer fan cycling. Have you actually listened for it before? How rapidly does it click? Does it still click on and off after the car has been sitting for a few hours / overnight?
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Newbie
Joined: Dec 2021
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From: Lake Wallenpaupack Pa
2014 G550
im having the same exact problem but my 20 it. When I pulled the clicked relay out and put it back in it stopped clicking and the car started up again. IM still researching it and ordering new relays.14 G550 died while driving
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Thread Starter
Member
Joined: Apr 2012
Posts: 80
Likes: 7
2012 ML350
What is happening is the main battery is used to keep the accessory battery charged. This is what enables you to lock/unlock the doors and operate other electronics while the car is off. It is vital that this battery be kept charged.
The clicking is when the accessory battery falls below a certain voltage and it switches on the main battery to top it off. The constant clicking was a warning to me (unknown at the time) that my accessory battery is no longer holding a charge.
And by association, it was putting undo stress on the main battery.
Not long after, I needed to replace my main battery as well. With both fairly new, the clicking only occurs when I open the car door and then only for a short time. Then it's gone. In addition, I got into the habit of putting my ML on a battery tender (Ctek-7002 AGM setting) when I am not planning on using the car for more than a day. This has worked wonders as it keeps both batteries at full charge when not in use.
Newbie
Joined: Dec 2021
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From: Lake Wallenpaupack Pa
2014 G550
I meant to say my 2014 G550. I also replaced both batteries a couple months ago but still have the clicking and car wont run. I will be replacing some relays and it appears the alternator is working
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From: Colorado
G550
My '19 G550 gurgles, burps and farts all the time while parked in my garage. Found a guy on linkedin who claims to be an automobile exorcist. Still checking his references. Will follow up.
