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Joined: Mar 22 2016
Posts: 1171

So to cut a long story short, I had an intermediate battery drain, I did the usual tests a few times, but it never showed anything, I replaced battery, power and earth leads, starter ( as would crank slowly, then fast), alternator and fitted one of Marty and nicks RF filters, all to no avail, so the other morning at 4am I was bored, so went out to the car, again a flat battery, I sat comfy with my cup of tea and again locked the doors, low and behold it didn’t go to sleep ( had on 2 previous tests)
So sitting there with thoughts of setting fire to it I started thinking what would cause it, I started at the pir sensor, pulled it out, blew into the sensors, sprayed the electrical connectors, plugged it back in and low and behold the bugger when to sleep, so £350 spent was down to either dust or a dirty connection,, been fine for past 5 days ( used to get hours sometimes) so looks like it’s cured,,👍

Edit, PIR is not a PIR, it’s a UMD or a USMD, but I know what I meant

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Joined: Dec 30 2015
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Great spot! So your P38 is slowly edging away from the flames?

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Joined: Jun 17 2018
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Great result!

What is a PIR sensor?

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Joined: Dec 30 2015
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A PIR sensor is a Passive Infra Red sensor, the sort of thing that detects movement and switches outdoor lights on or triggers a burglar alarm. What Chris is referring to is actually an ultrasonic movement sensor and is the thing above the passenger side B post.

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Joined: Jun 17 2018
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Ahh thanks..

Might clean mine!!

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Joined: Mar 22 2016
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Morat wrote:

Great spot! So your P38 is slowly edging away from the flames?

I’d say the lighter is still in my hand, it better behave,, 😂🤣

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Joined: Mar 22 2016
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So, it’s back, came out yesterday and dead battery, this is driving me insane, any ideas before I torch the bloody thing.. 🔥

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Joined: Feb 24 2017
Posts: 166

You could open the fuse box and take out the top line of fuses overnight and see if the battery drains.
If not, replace the top line and remove the 2nd line of fuses and see if battery drains..
If you remove one line of fuses and find there is no drain on battery then you know the discharge is caused by one of the items on that line of fuses. Then reset all fuses and take two out at a time as above.
Probably not the most technical way to find a battery draw but at least it will keep your mind busy and your finger off the lighter for a week or so....

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Joined: Mar 22 2016
Posts: 1171

Lighter, I’ve got self igniting blow torch,, lol, it’s most probably something really silly, but when you go out and it’s touch and go wether or not it will be flat it gets annoying, especially this year as my arthritis has kicked in hard, so not very mobile ☹️

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Joined: Apr 23 2019
Posts: 334

Is it close enough to the house to leave the battery on a smart charger (at least then you have reliability)? Is your alternator definitely charging properly? For a few pounds you can get a usb socket/ voltage indicator to put in the cigarette socket and it will give you the voltage of the battery/ alternator charge - just eliminates some guess work. Perhaps unplug the blue RF receiver overnight to see if anything changes, other than that JMCs method seems as good as any

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Joined: Mar 22 2016
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Yes, I fitted a new one as a precaution, if I catch it and it fires up, 5 minutes running and it cranks over like a mini with a lorry battery on, when I cleaned the movement sensor, I got 8-9 days before it went into drain mode, I think I’m gonna have to get it down to my stepfathers garage in the next week or so and spend some time playing with it, I can’t do it out in the cold, 20 mins and I’m in agony,,

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Joined: Mar 22 2016
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So my saga continues, Sunday I fired her up to go out with the dog, and after a minute it shut down like I’d pulled a lead off, was instant, the battery was zapped of all juice at the same time, I’m thinking there’s a dead short somewhere, so it’s going into garage ( nice and warm ) and I’m gonna play till I find the problem, I suppose 5 years with no problems was good,, but now it’s gonna retaliate 🤣😂

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Joined: Sep 02 2016
Posts: 476

Odd to start and then just die like that of course....

As part of your investigation (in the garage) consider removing the earth lead from the battery and wire an analogue 0-5A meter in series with it instead. Lock the car and monitor the meter... regularly... and if there is excessive current draw (after the BECM has gone to sleep) proceed from there - ie. removal of individual fuses to find the cause/s. It would take a few amps (continous) overnight to cause the flat battery of course.

-These meters are just a few pounds on ebay of course... and will happily melt if (Ooopps) you forget it is there and maybe try to start the car...

Alternatively use a cig. lighter led voltmeter (as already suggested); Lock car monitor.

Don't know just how many charge/(complete) discharge cycles you have endured but the battery will not like this either !

Like many I have had BECM staying awake (RF interference), faulty cell on battery and a wet fusebox (condensation) cause this kind of problem.
Similarlyan internal light staying on does not help either...
Good Hunting !

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Joined: Mar 22 2016
Posts: 1171

I’ve cleaned all the earths and replaced leads, replaced fuse box, alternator, starter motor, battery ( checked today, still showing as good ) rf filter, the drain can be minutes or hours, I’m gonna pull every fuse, and replace one every 12 hrs, see how I go, lol

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Joined: Sep 02 2016
Posts: 476

Might take a while that Chris ! Are you sure frying a few of these (or similar) would not be quicker ?! ebay 302919434102

Incidentally I first used this method when I tired of sitting inside the car like some kind of Ninja waiting for the dim 'P' led to go out.....!

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Joined: Jan 05 2016
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This is one of my favourite cheap tools - a Uni-T AC/DC clamp meter. Has a 2, 20 and 100 amp scale on both AC and DC current testing.

Makes non-invasive battery drain testing (or general current monitoring) very simple and safe. Very much a must have for a P38 owner I'd say if you're having battery issues.

https://www.amazon.co.uk/UT210E-Current-Meters-Capacitance-Tester/dp/B00O1Q2HOQ

I actually lost it (in the house... somehow) for a few months and missed it enough I nearly bought another one before finding it.

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Joined: Sep 14 2016
Posts: 426

Probably got something similar to that cheap meter in the big box of meters I have kicking about the place if anyone wants a freebee. Probably be a couple or three quid to post tho'.
Done my back in yesterday so it'll be a week before I can reach up and get the box down off the top shelf.

I like the meter Sloth suggests. Looks like they have finally sorted the economical DC clamp meter thing. And with a usefully low current ranges too. Maybe its time to get one for myself.

Need to watch the specifications if going for a different "looks the same" breed. The real cheapies will almost certainly not have DC current capability or if they do only on a very high range. I imagine you could easily pay more for less. Looked into this a year or so back for a guy who I was not going to lend my clamp meter to and it was a minefield. My clamp meter is AC only but its a good few years old.

Clive

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Joined: Nov 16 2016
Posts: 944

I've always checked for battery drain by just disconnecting a connector from the battery and using a multimeter on Amps setting.. If the car draws too much current for the ammeter when (say) the battery is first connected or if you need to start the engine just hold the connector on the battery during that time or use a jump cable in parallel with the ammeter.

The clamp tool in the link looks a good bit of kit, great reviews, tempted myself but would probably never use it.

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Joined: Dec 30 2015
Posts: 1752

One of the fun parts of P38 ownership is that things can escalate quickly if you disconnect the battery. At the very least you've got to reset all the windows and sunroof. If you mess it up you'll be entering the EKA and hoping that your door lock switches are all working or you've got a nanocom to hand.
That's assuming you haven't left your only key in the ignition ;)

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Joined: Jan 05 2016
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I just find it a lot easier than using a traditional ammeter or multimeter in line - and it can be used in many situations where you might not want to cut into cabling if it cant be disconnected already. Or as Morat says, you don't want to risk a battery disconnection.

Plus... you're not limited to 10 or 20 amps like most meters - if the current suddenly spikes, nothing goes pop - the meter might go out of range but that's it. My BMW will sit there with the keys out, sucking 20 amps, if the welcome home lights etc come on. Measured with the DC amp clamp, don't you know :)

Uni-T, I'll take a cheque for the plugging ;)