P38A Rear screen heater

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Sonnycbr said:
Took car to auto electrician today. Alternator fine. They’ve found a 50 amp fuse under the bonnet that’s creating a massive drain continuously and appears to do nothing. . If the car starts tomorrow and everything seems ok I’ll leave it out but has anyone heard/seen anything like this? The sparky says the only thing he’s seen like it was on a BMW engine and it was a heater.
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Under the fusebox? Like an inline one? Does it have a voltage sensitive switch near it? Thinking someone might have wired it in for the towbar caravan electrics rather than use the built in ones at the back that are controlled by the BECM.
 
Sonnycbr said:
Took car to auto electrician today. Alternator fine. They’ve found a 50 amp fuse under the bonnet that’s creating a massive drain continuously and appears to do nothing. . If the car starts tomorrow and everything seems ok I’ll leave it out but has anyone heard/seen anything like this? The sparky says the only thing he’s seen like it was on a BMW engine and it was a heater.
Click to expand...
"Alternator fine" did the electrician say what the charge voltage was?
50amp fuse under the bonnet? Is that in the under bonnet fuse box where there are several mega fuses?
 
Grrrrrr said:
Under the fusebox? Like an inline one? Does it have a voltage sensitive switch near it? Thinking someone might have wired it in for the towbar caravan electrics rather than use the built in ones at the back that are controlled by the BECM.
Click to expand...
I don’t think it’s ever had a tow bar fitted, certainly no signs of one. I haven’t picked the car up yet, only spoke to garage. I’ll find out in the morning and post pics. Thanks for the reply.
 
Datatek said:
"Alternator fine" did the electrician say what the charge voltage was?
50amp fuse under the bonnet? Is that in the under bonnet fuse box where there are several mega fuses?
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He didn’t say what the charge voltage was but I’ll ask him in the morning. I took him to mean that this fuse was in the fuse box under the bonnet. All should be more clear in the morning.
 
Ok, collected car this morning. The fuse in question is FL4 in the engine fuse box. Apparently it s linked to lots of things but it’s a continuous drain on the battery. I’m sure he said over 10A. When disconnected the drain dropped to about 1.5A which I think is right until it all goes to sleep.
Apart from disconnecting the fuse when I’m not using the car, what do you think I can do? Do I need a new BECM or is that not a good idea? As always, I’m open to any and all advice.
 
Sonnycbr said:
Ok, collected car this morning. The fuse in question is FL4 in the engine fuse box. Apparently it s linked to lots of things but it’s a continuous drain on the battery. I’m sure he said over 10A. When disconnected the drain dropped to about 1.5A which I think is right until it all goes to sleep.
Apart from disconnecting the fuse when I’m not using the car, what do you think I can do? Do I need a new BECM or is that not a good idea? As always, I’m open to any and all advice.
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I'll look into what might cause a drain on the fuse line and get back to you.
Replacing the BECM is always a last resort, most often these problems are nothing directly to do with the BECM but it's an easy thing to blame.
14.4 volts is OK.
 
Datatek said:
I'll look into what might cause a drain on the fuse line and get back to you.
Replacing the BECM is always a last resort, most often these problems are nothing directly to do with the BECM but it's an easy thing to blame.
14.4 volts is OK.
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That’d be great, much appreciated.
 
OK, Maxi Fuse 4 feeds the following circuits via the BECM, these are in the under seat fuse box.
F12 Heated screen & LH rear window.
F13 shift interlock and sunroof.
F14 Central locking rear doors, fuel flap and trailer socket
F15 Courtesy lights ,rear wiper and radio stuff in the rear
F17 Brake switch.
Relay 10 inside the BECM which then feeds F7 Auto box & transfer box ECU's and F5 photochromic rear view mirror and sun visor lights.
So, pulling those fuses one at a time should allow you to narrow down the source of the drain. My bet would be on F12 which feeds the heated screen via the HEVAC.
 
Datatek said:
OK, Maxi Fuse 4 feeds the following circuits via the BECM, these are in the under seat fuse box.
F12 Heated screen & LH rear window.
F13 shift interlock and sunroof.
F14 Central locking rear doors, fuel flap and trailer socket
F15 Courtesy lights ,rear wiper and radio stuff in the rear
F17 Brake switch.
Relay 10 inside the BECM which then feeds F7 Auto box & transfer box ECU's and F5 photochromic rear view mirror and sun visor lights.
So, pulling those fuses one at a time should allow you to narrow down the source of the drain. My bet would be on F12 which feeds the heated screen via the HEVAC.
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That’s brilliant. As you know, I thought I had a problem with the heated screen but I also had a problem with the LH rear window, it wouldn’t roll up from the drivers seat.
Thank you so much.
 
Removed F12 but rear window still operating. . Don’t know about rear screen heater. I’ll pay another visit to sparky and try removing one fuse at a time to see if there’s still a drain.
Could I do the test myself? If I use meter across battery terminals I should see voltage dropping until I remove offending fuse. Correct??
 
Apologies, I’d removed F22. I wondered why the front windows suddenly went off. Busy all weekend so F4 back out as well as F12. I’ll have a look on Monday.
 
Sonnycbr said:
Removed F12 but rear window still operating. . Don’t know about rear screen heater. I’ll pay another visit to sparky and try removing one fuse at a time to see if there’s still a drain.
Could I do the test myself? If I use meter across battery terminals I should see voltage dropping until I remove offending fuse. Correct??
Click to expand...

You need a digital volt meter (DVM) or clamp meter. Assuming draw isn't too high it should take it. You could always rig up an inline fise but you'll probably get away without.

Disconnect the battery negative. Charge it overnight.

Using a jump lead, drop the lead through a gap to underneath the car from the disconnected negative cable and connect to the DVM red lead with the DVM set to amps. Connect the other jump lead to the negative battery terminal and drop it down a gap so you can shut the bonnet.

From the other DVM cable connect to the other jump lead. The battery is now connected through the DVM. Anything drawing current will show on the DVM.

The BECM will be awake for a while but after 20 minutes the amps should drop. You may be able to click the door latch shut with a screwdriver and then lock the car but if not you'll have to **** the door and lock and wait each time until it goes to sleep.

One at a time, remove a fuse and see if the current draw drops. The BECM takes about 125mA? (? Check RAVE as a long time since I did this) but anything above that is parasitic draw. One fuse should make a difference but the others won't. That one has the circuit with the issue.
 
Grrrrrr said:
You need a digital volt meter (DVM) or clamp meter. Assuming draw isn't too high it should take it. You could always rig up an inline fise but you'll probably get away without.

Disconnect the battery negative. Charge it overnight.

Using a jump lead, drop the lead through a gap to underneath the car from the disconnected negative cable and connect to the DVM red lead with the DVM set to amps. Connect the other jump lead to the negative battery terminal and drop it down a gap so you can shut the bonnet.

From the other DVM cable connect to the other jump lead. The battery is now connected through the DVM. Anything drawing current will show on the DVM.

The BECM will be awake for a while but after 20 minutes the amps should drop. You may be able to click the door latch shut with a screwdriver and then lock the car but if not you'll have to **** the door and lock and wait each time until it goes to sleep.

One at a time, remove a fuse and see if the current draw drops. The BECM takes about 125mA? (? Check RAVE as a long time since I did this) but anything above that is parasitic draw. One fuse should make a difference but the others won't. That one has the circuit with the issue.
Click to expand...

That’s what I’ll do. The sparky said the draw was that high the cables on his meter were hot. Just to be clear, I connect jump leads to the negative lead and negative terminal, then connect DVM to the jump leads? Nothing to go on the positive side?
 
Grrrrrr said:
You need a digital volt meter (DVM) or clamp meter. Assuming draw isn't too high it should take it. You could always rig up an inline fise but you'll probably get away without.

Disconnect the battery negative. Charge it overnight.

Using a jump lead, drop the lead through a gap to underneath the car from the disconnected negative cable and connect to the DVM red lead with the DVM set to amps. Connect the other jump lead to the negative battery terminal and drop it down a gap so you can shut the bonnet.

From the other DVM cable connect to the other jump lead. The battery is now connected through the DVM. Anything drawing current will show on the DVM.

The BECM will be awake for a while but after 20 minutes the amps should drop. You may be able to click the door latch shut with a screwdriver and then lock the car but if not you'll have to **** the door and lock and wait each time until it goes to sleep.

One at a time, remove a fuse and see if the current draw drops. The BECM takes about 125mA? (? Check RAVE as a long time since I did this) but anything above that is parasitic draw. One fuse should make a difference but the others won't. That one has the circuit with the issue.
Click to expand...
Asleep, the BECM draws between 35 & 50ma.
 
Sonnycbr said:
That’s what I’ll do. The sparky said the draw was that high the cables on his meter were hot. Just to be clear, I connect jump leads to the negative lead and negative terminal, then connect DVM to the jump leads? Nothing to go on the positive side?
Click to expand...

If draw is that much you'll need an inline fuse and a shed load of spares. Never used a clamp meter but others can probably advise on its use.
 
Ok, here's what's happened. I removed F12 and left it out, car starting straight away with obvious power in the battery. I kept getting a warning saying F12 was missing. This was coming up on the dash and beeping constantly. I had a bit driving to do that day and the warning still came up on the dash with a short beep, but only on start up. My plan going forward is to live without F12 and bollocks to the rear heated screen and real LH window. The electrician said he'd remove the plug from the LH rear door and do a test but I've spent enough on this fault. I want to thank all of you for your help, this car would've been long gone if it hadn't been for your help. PS, that's a compliment!:p
 
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