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Discussion Starter · #1 ·
I unfortunately bought a 2010 megane dynamique a few months back which has been back to the car sales for about 5 months out of the six since bought. The garage have now dropped it back to me having given up trying to rectify the fault. The fault is the battery has a current drain with everything off of over 3 amps. The last thing the garage fitted was a new alternator which made no difference at all. Has anyone any clue as to what could be causing this high drainage current, which equates to just under 40 watts, about the same as a headlight bulb. Many thanks and please nobody say it's a faulty battery
 

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I've edited your title, better then just your name.
What fuel and engine Geoff.... will make a difference.

Basic is that you need to disconnect each circuit and identify where the drain occurs...then zero in.
But give us the above and we can suggest common areas to look at.

PS...not a faulty battery is it?
191866
 

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Discussion Starter · #3 ·
Many thanks for your replies and interest, much appreciated. The car is diesel, engine size 1499cc
 

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I have same car same year same dynamique spec! Amazed they would change the alternator that's a costly job!! They are good for 100-150,000 miles.

Are you sure every single thing is turned off when you switch the engine off? As even leaving the aircon or lighting switches on & the engine is switched off produces a small drain which quickly adds up to flatten batteries over time!

Always ensure every single electrical system is turned off fully when you lock the doors after the engine has been switched off. These cars tend to drain the batteries rapidly. Could be a faulty door sensor the lightbulbs in the door card within 3-4 hours drain the battery totally if its left partially open (say a mechanic is working on your car did not shut the door(s) properly). Way to test this is remove the interior door bulbs then see if it still drains (easy to remove just gently pry the covers out then gently push the bulbs out-they get very hot so watch out).

If you plan to keep the car upgrading the interior lights to canbus friendly LEDs is a great cheap mod which saves draining the battery:
Renault Sport Megane 250/265 - PremiumKit (renaultsportclub-shop.co.uk)
 

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40W is a helluva lot..(as you say over 3A) - something somewhere must be getting warm if not hot, I'd suggest a infra red imager but they are very expensive (unless you know someone from whom you could borrow one...) anyway as that isn't likely..moving on
I assume you've found a way of measuring it? Do you have a clamp meter? (saves having to disconnect the battery suggest you look at uni-t 210 meter)
If you only have a cheap meter it will need a 10A range, and even that will present significant resistance, and if you operate the central locking while it's in circuit it may overload, so a clamp meter is your best bet.
First port of call. Have you tried disconnecting the radio? Is it warm or hot to the touch? (make sure you have the code)
Or however you measure it get the meter indicating the drain, then you need to start pulling fuses out one at a time to see if it stops the drain at any point.
You could also try disconnecting the plugs from the fusebox under the bonnet that will at least tell you if it's going through that path. If that stops it reconnect and pull individual fuses there.

A lamp isn't 40W generally no more than 5, so it's unlikely to be a rogue lamp.
There must be more clues, has it been scanned for fault codes?
 

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Discussion Starter · #6 ·
I have same car same year same dynamique spec! Amazed they would change the alternator that's a costly job!! They are good for 100-150,000 miles.

Are you sure every single thing is turned off when you switch the engine off? As even leaving the aircon or lighting switches on & the engine is switched off produces a small drain which quickly adds up to flatten batteries over time!

Always ensure every single electrical system is turned off fully when you lock the doors after the engine has been switched off. These cars tend to drain the batteries rapidly. Could be a faulty door sensor the lightbulbs in the door card within 3-4 hours drain the battery totally if its left partially open (say a mechanic is working on your car did not shut the door(s) properly). Way to test this is remove the interior door bulbs then see if it still drains (easy to remove just gently pry the covers out then gently push the bulbs out-they get very hot so watch out).

If you plan to keep the car upgrading the interior lights to canbus friendly LEDs is a great cheap mod which saves draining the battery:
Renault Sport Megane 250/265 - PremiumKit (renaultsportclub-shop.co.uk)
many thanks for your info, I have checked that the interior lights switch off ok.I am at a total loss to think what could be consuming 40 watts, but not visible or audible.
 

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Discussion Starter · #7 ·
many thanks for your info, I have checked that the interior lights switch off ok.I am at a total loss to think what could be consuming 40 watts, but not visible or audible.
Will try disconnecting the plugs on the under bonnet fuse box first and see if that stops it-many thanks again
 

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Might not help at all but when you lock the car do you dead lock it using the key fob?
Ie, press the lock button twice?

If so, try that and report back. I read another member on his RS had a drain stop when he did this.
Not sure why.

My Megane sounds like it long cranks, hesitates for a second before firing most days. I have wondered the same, if I have a drain somewhere.
 

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many thanks for your info, I have checked that the interior lights switch off ok.I am at a total loss to think what could be consuming 40 watts, but not visible or audible.
You have a minimum of 7 x interior visible light bulbs alone (excluding the instrument panel). All use a lot of battery power as older bulb technology not modern low power LED bulbs. Mine drained totally after just a few hours when some mechanic left the door partially open!

1 bulb in the boot
1 bulb in the glovebox
2 x door card footwell bulbs on the coupe (4 x door bulbs if you have a 5dr megane)
6 x ceiling lights (3 bulbs near the mirror 1 bulb on the passenger ceiling)

Check the radio. Disconnect if possible. They can go faulty could be constantly playing tracks or keeping the amp powered up.

Check the aircon controls are really fully off (also lights behind the aircon dials but hard to access so leave for now its an awkward job!). At night is the only way to see if the aircon controls backlights are functioning its impossible to tell in the daylight!

Megane mk3 are great little cars for the money but electrics are always not as good as they could be due to that is where a lot of the cost savings were clearly made.

As someone else already said start pulling fuses see which one controls the drain item. Be careful though with what you pull you do not want to lock the alarm system!! Your handbook should have info on the fuses but there are also some other fuses not mentioned. 1 is I believe hidden in the engine bay, main fuse box is in the glovebox & there is even a fuse on the actual battery connectors as per the video below:
(3) Renault Megane battery fuse 32v - YouTube

If possible check door sensors if they are faulty then it might allow the door card lights circuit to operate even when the door is shut but that will be impossible to actually see so disconnect the door card lights they just gently pull out when you put something under the securing tab. I was shocked on mine one had rusty electrical connections (inside the door!) & they drain the battery fast if the door is not shut properly.

Check the boot light sensor as well by pulling that light out to isolate it. Then close the boot with no light see what reading you get.

40 watts drain can be a red herring. These meganes go haywire when the battery is low or knackered how new is yours anyone tested how much life it has left?
 

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@Renault-Megane-Mk3-2010
good point, I don't have a meg thus no below door lights so I don't know how well shielded they are from visibility when the door is shut, wouldn't you see a glimmer from them reflected on the sill in the dark if they were on? I also mentioned the radio but even if the amp was on 40W is a lot of quiescent wattage, I'd think it would be well below 1 amp. (unless it's a class A amp which it wont be).
I'd like to know how this is being measured.
 

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@Renault-Megane-Mk3-2010
good point, I don't have a meg thus no below door lights so I don't know how well shielded they are from visibility when the door is shut, wouldn't you see a glimmer from them reflected on the sill in the dark if they were on?
If the sensor is faulty then the light would be off but the battery drain is still present. Its a long shot if this is the problem or not just something to try!
 

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Discussion Starter · #13 ·
Thanks for all the info, there are def. no interior light on,have looked in total darkness and the radio is totally off. With this high current drain I was wondering of the possibility of the injector preheaters being on, any thoughts?
 

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Discussion Starter · #14 ·
Further to my last post, I wondered about the possibility of a stuck closed relay,of which there are dozens, that is not dependant on the ignition being on, or am I talking rubbish
 

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It could be anything, a stuck relay is as likely as anything else at this stage. Just because the radio is off or looks as though it is, doesn't mean it isn't drawing any current. Make sure you have the code if you disconnect it.
Are the windscreen wipers working and parking OK?
How are you measuring the drain? (asked again), 3A is very high. Bear in mind it could be a concatenation of more than one drain.
 

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How are you measuring the drain? (asked again)
.............and still.

The subtlety of this is:

If you remove one of the battery cables and insert a current meter (or multimeter on current setting) you are in effect inserting a high resistance path into that particular cable's connection to the battery - the meter has a limited range of measuring as well as a fuse. Its quite conceivable and it does happen that when you now reconnect the battery with the current meter inserted, that the required voltage by all computers ALL AT ONCE upon connection is below spec and that may put the computers into a comatose mode where they forget what their purpose in life is ................. and I have seen them forget to go to sleep.

The correct way is to use a DC current clamp on either battery terminal lead - this ensures you don't have an unknown/uncertain starting point with the computers.

The same current clamp can be used on each and every wire in the car individually to see which one is carrying the current..........................
 

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Discussion Starter · #17 ·
Hi, I'm measuring the drain using an expensive multimeter on 10 amp range. Also as absolute proof the battery drain is such that the engine will not turn over after a few hours. Wipers and parking? ok
 

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Hi, I'm measuring the drain using an expensive multimeter on 10 amp range. Also as absolute proof the battery drain is such that the engine will not turn over after a few hours. Wipers and parking? ok
ok then ............... irrespective of the cost and the brand of the meter, if its an item you insert into one of the battery leads my comment stands.

Read what I said again - no use getting upset with me - I am NOT disputing the fact the battery gets drained
 

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@LvR @fedupgeoff
I covered that earlier (clamp meter), and I agree that's why I kept on asking how it was being measured...I even suggested one which is sensitive but relatively inexpensive. You can probably get it cheaper if you search around.
You can eliminate the pre heaters by disconnecting?
Re the meter, firmly connect across the terminal and cable BEFORE you disconnect the terminal then as you disconnect watch the behaviour of the meter, does it instantly go to 3A, or does it start low and eventually settle at 3A?
(I'm curious...Why would a garage replace an expensive alternator on a whim? What have they replaced it with, is it a refurb? and are you sure the replacement is OK, have you measured the charging voltage?)
@fedupgeoff you said not to suggest it was a faulty battery so I won't but I will ask has the battery been checked with a proper tester (not a multimeter)? What do the battery volts measure when you've charged it and after a few hours?

later edit
Have any extras been fitted to the car that you know of (cameras, satnav, sensors etc)?
 
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