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OK, I'm a bit stumped! We have a 40K mile 1999 Golf Mk4 auto, which is completely untampered with. Been 100% reliable up until now. 1 week ago, drove 10miles in heavy rain at night. Stopped for 5 mins, and then the car wouldn't start - turned over healthily for 10secs, turned off, tried again but sounded as thought the battery was struggling. Turned off, tried again and just clicking. Usually starts immediately. Jumped started it from another car v easily, ran fine to home, put it on charge overnight. Started perfectly next morning. But then not used for the day and the next day, battery struggling and not enough power to start it.
Coincidentally, the rear passenger door lock jammed (son slamming it at lot), so I removed it. Look like a mechanical stickiness so I've replaced it with a new ebay one which locks/unocks and works fine.
Since then I have monitored the battery -
- it holds charge when disconnected for 2 days
- bought a Ctek smart charger and fully charged it
- battery voltage at idle 14.65V
- battery voltage after charge 12.8V
- have tested battery drain and it's pulling 83mA with everything off
- removed each fuse and fuse 14 (central locking/interior lights) reduces drain to 63mA
- no other fuse affects drain (and I understand an acceptable rate should be <50mA)
- have removed alternator fuse 110A and no affect on drain
- have checked battery earth and lovely and clean, as per other earths I can see
- have pulled rubber covers on doors and boots to check wiring- Found 1 brown wire on boot hinged that had snapped, have resoldered - no change on drain
- have removed orginal unit stereo
- have removed interior bulbs
- have removed glove box light unit
- have disconnected CCM unit
So, qns are:
- if it's a dodgy central locking lock, then wouldn't removing the fuse for central locking isolate this from the drain?
- could my new lock be dodgy, but as above re fuse removal
- the car has been 100%, but failed to start after a 10mile journey in the wet ... could it be damp affecting something?
- Fuse 14 obviously has some affect, but 63mA is still more than the suggested rate of <50mA
I'm stuck! Any help would be great
Very thorough and I stopped reading. How old is your battery? Cars driven infrequently on shortish trips are not well suited to modern cars and their electrical requirements when sat in a driveway.
My 58 plate Mazda6 is 2020’s testament to this. I now use my ctek charger every few weeks to keep the battery conditioned.
Have you done the obvious and purchased a new battery?
Hi ... not sure of battery's age. I had assumed (wrongly?) that if it was holding >12.6V for a couple of days (left outside in the cold) then it was OK. And have a Ctek charger with a recondition mode which I have run on it last night.
Maybe I should get it drop tested tomorrow?
And have just disconnected the new lock and that hasn't impacted the drain, so assume the new lock is mechanically and electrically ok.
Dont bother getting it tested just replace it, £90 will get you a new Bosch one from euro car parts and fit it yourself. If you arent sure how old it is it's probably too old and proper cold weather is always when it shows.
You've said yourself that you've pretty much eliminated everything else.
Wow, very thorough. But I’d also bet a packet of Werther’s it’s the battery. You can always keep the old one as a spare if it seems to hold its charge ok.
Also on my Shaguar a number of the modules stay active for a few minutes after switching off, so could this be affecting your drain readings?
Thanks and probably a good course of action to replace the battery.
Still intrigued why removing fuse 14 drops the drain from a very steady 83mA to 60mA?
Still intrigued why removing fuse 14 drops the drain from a very steady 83mA to 60mA?
Most likely as the locking module is still awake (see timbog160’s post). The definition of On and Off on a car has been blurred for many years. Long gone are the days of “off - accessory - engine run - crank” being a direct link to whether something is powered or not. Back in the early 90s, a 30sec power sustain after “key-off” for the powertrain control unit was pretty standard at the OEM I worked for. Similarly any remote functions (from central locking upwards) needs at least one (more these days) module to be at a minimal level of “awake”.
Thanks TedC ....out of interest then to a do an accurate drain reading, should the car be locked, manually close the bonnet latch, leave it alone for 10mins, then do a reading?
Golf MK 4 2001 manual here - I think our drain was > 60mA and we never experienced the issues you describe (after market alarm pulling the power).
Sounds like something else rather than parasitic drain if it started OK > drove OK > failed to start after 5 mins.
As above, most probably the battery is knackered but it could be the charging system - check the aux belt? Is the alternator sounding off at all?
And as above, look into getting a good maintenance charger (you can wire in a plug to avoid battery box faf).
OK, I think, a breakthrough. I had pulled the OE radio cassette out and disconnected. But I've just pulled fuse 42 which is the radio fuse and drain fell to 39mA. So, fingers crossed ... albeit I'm confused as to why with the radio disconnected there was still a draw. But will leave it locked now, battery connected and see what it's like in the morning.
Just to put it into perspective....assuming you have a 90ah battery, a drain of 83ma would take over a thousand hours to drain the battery - thats assuming my non electricians calculations are correct (which they may well not be 😀). But I admire your persistence!
My most frustrating battery drain experience was my ex army Wolf Land Rover. Would start and run ok but would sh*g batteries in a matter of hours. Turned out the glow plug timer relay had sticking contacts so it was putting 60 amps out constantly - now that will do your battery!
Probably just the battery.
In terms of battery drain, modern vehicle guidelines is it'll take up to 20-30 minutes for all modules to fully shut down. Most will usually shutdown within 5 minutes, but for diagnostic purposes, a minimum of 15minutes is the usual advice.
To test for battery drain, you ideally need to set the vehicle up so it thinks all doors/bonnet/boot are closed, lock the vehicle, leave it for 15 minutes, and then measure battery drain without opening anything, or breaking the battery circuit.
I'd be looking for sub 20mA after that time. If it was still above that after 30minutes, I'd let it sit overnight and recheck.
Any update OP? Did the battery survive the night?
Two sentences in I was thinking "20 year old battery + lockdown restrictions + winter = donald ducked."
I'd be checking that the plug / rectifier pack into the alternator wasn't pissed wet through / corroded also.
If the battery is older than, say, 5 years then replace it.
Very nice and fairly exhaustive diagnostic process. I’d have focused on what’s changed recently: car stasis* and fairly cold weather. Like folks said already: dying battery.
* though you don’t describe the car’s activity in the few weeks preceding the 10mile drive.