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Flat battery, v. high current drain - Fuse No. 8 under bonnet. Water pump continuous...

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Flat battery, v. current high drain - New info...

Post by Newbers » Fri Nov 03, 2017 10:22 pm

ph001 wrote: Fri Nov 03, 2017 9:59 pm OP, have you had a good feel around the fuse box for anything getting warm as previously suggested?
Not yet - I was a bit pushed for time. Initial indications are that it will be a fuse in the box under the bonnet rather than in the cabin. I'm basing this on the fact that one of the red cables off the battery showed only very low (expected current). The other which I think is the fancy one that runs under the car, to the JB on the bulkhead (I think). I'm registering a good few amps on conduits coming in to and out of the smaller fuse box under the bonnet so (again I think) the fuse protecting whatever is at fault is in that smaller black fuse box.

I'm struggling about to find a wiring diagram that covers the electrical stuff on the engine. I've got the WDS disc here but the only laptop with a DVD slot has an old version of Java and I can't get it on my wifi to update :-x !
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Flat battery, v. high current drain - Fuse No. 8 under bonnet...

Post by Newbers » Sat Nov 04, 2017 2:54 pm

It finally stopped raining long enough to go and get a bit deeper in to this. In this fuse box under the bonnet:
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IMG_1448[1].JPG (272.8 KiB) Viewed 940 times

fuse No. 8
IMG_1447[1].JPG
IMG_1447[1].JPG (168.09 KiB) Viewed 940 times
is the one that is carrying the load (an indicated 14A acknowledging Mike's comments about multiple cables in the bundle). The fuse was warm.
No key in ignition but definitely got a whirring noise somewhere at the front of the engine. I wasn't in a position to be able to get underneath but just wondering about the water pump. I'm aware of water pump problems (not sure if these are with N52 engines) but my understanding is these normally fail off. Just wondering if there could be a problem with the thermostat which is causing the pump to default to on.

Can anyone tell me what that fuse no. 8 is actually for?

Also - anyone got a wiring diagram that covers engine functions or a map of the fuses in this box?
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Flat battery, v. high current drain - Fuse No. 8 under bonnet...

Post by ph001 » Sat Nov 04, 2017 9:11 pm

I'm assuming if you pull that fuse the whirring stops? You would even feel the water pump buzzing if it was running so that is your first port of call. Really struggling to fund any info on under bonnet fuses. Here are the glove box ones just for future ref.. viewtopic.php?f=3&t=38888

The water pump would fit the bill at that sort of current draw, but yes....unusual for them to fail always on. It certainly can run with the ignition off though if the coolant temp is >90'c so you could see how a fault could give you the problem you are seeing. The stat itself has no sensors on it so is completely autonomous. I'd probably still be tempted to change though if you end up doing the pump.
Last edited by ph001 on Sat Nov 04, 2017 9:18 pm, edited 1 time in total.
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Flat battery, v. high current drain - Fuse No. 8 under bonnet...

Post by Ewazix » Sat Nov 04, 2017 9:17 pm

Previous topic might help viewtopic.php?t=90594
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Flat battery, v. high current drain - Fuse No. 8 under bonnet...

Post by andyfanshawe » Sat Nov 04, 2017 9:20 pm

Pulling fuses to check for a parasitic draw is not a good idea with modern cars. It is not an accepted practice anymore.

Modules shut down as their power supply is interrupted, then take ages to go back to sleep. Sometimes as long as 20 minutes. Get a normal multimeter and shut as many things as you can (doors, boot, bonnet etc) and put the multimeter leads across each fuse in turn. Right at the top of the fuse. Those 2 metal bits. DC voltage scale. Small range. 2V or less.
If the circuit is active there will be a very small voltage drop across the fuse. If it is not active, it will be 0. The slightest reading (no matter how small, and it will be small) is a sign of current draw.

Andy

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Flat battery, v. high current drain - Fuse No. 8 under bonnet...

Post by Smartbear » Sat Nov 04, 2017 9:26 pm

andyfanshawe wrote: Sat Nov 04, 2017 9:20 pm Pulling fuses to check for a parasitic draw is not a good idea with modern cars. It is not an accepted practice anymore.

Modules shut down as their power supply is interrupted, then take ages to go back to sleep. Sometimes as long as 20 minutes. Get a normal multimeter and shut as many things as you can (doors, boot, bonnet etc) and put the multimeter leads across each fuse in turn. Right at the top of the fuse. Those 2 metal bits. DC voltage scale. Small range. 2V or less.
If the circuit is active there will be a very small voltage drop across the fuse. If it is not active, it will be 0. The slightest reading (no matter how small, and it will be small) is a sign of current draw.

Andy
Hi, I’m surprised that a voltage drop can be measured across the fuse? After all it’s a single piece of wire in effect (if it’s not blown!) I would have expected to read 0v measuring across it this way :?
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Flat battery, v. high current drain - Fuse No. 8 under bonnet...

Post by ph001 » Sat Nov 04, 2017 9:36 pm

If there is current through the fuse it will have a volt drop across it but it will be small (milli volts). I don't see any issue in pulling it to see the effect though to be honest, despite it not being best practice.

The OP already knows fuse 8 has current through it as it is warm.
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Flat battery, v. high current drain - Fuse No. 8 under bonnet...

Post by andyfanshawe » Sat Nov 04, 2017 10:31 pm

Smartbear wrote: Sat Nov 04, 2017 9:26 pm
andyfanshawe wrote: Sat Nov 04, 2017 9:20 pm Pulling fuses to check for a parasitic draw is not a good idea with modern cars. It is not an accepted practice anymore.

Modules shut down as their power supply is interrupted, then take ages to go back to sleep. Sometimes as long as 20 minutes. Get a normal multimeter and shut as many things as you can (doors, boot, bonnet etc) and put the multimeter leads across each fuse in turn. Right at the top of the fuse. Those 2 metal bits. DC voltage scale. Small range. 2V or less.
If the circuit is active there will be a very small voltage drop across the fuse. If it is not active, it will be 0. The slightest reading (no matter how small, and it will be small) is a sign of current draw.

Andy
Hi, I’m surprised that a voltage drop can be measured across the fuse? After all it’s a single piece of wire in effect (if it’s not blown!) I would have expected to read 0v measuring across it this way :?
Rob
If the resistance is zero, there will be zero volt drop. But a fuse has a resistance (so has a cable or wire) so there will be a voltage drop. The resistance will be very small though, so the voltage drop will be also.
The key here is if the multimeter reads anything at all, there is current flow in that circuit.

Interesting isn't it?

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Flat battery, v. high current drain - Fuse No. 8 under bonnet...

Post by andyfanshawe » Sat Nov 04, 2017 10:48 pm

ph001 wrote: Sat Nov 04, 2017 9:36 pm If there is current through the fuse it will have a volt drop across it but it will be small (milli volts). I don't see any issue in pulling it to see the effect though to be honest, despite it not being best practice.

The OP already knows fuse 8 has current through it as it is warm.
Thank you for your honesty!
It is not best practice because it is interrupting power to modules. You then have to wait possibly 20 mins + for it to go back to sleep once the fuse is back in. Any current monitoring during that time will be inaccurate because the module(s) are still consuming current.
Checking across fuses in circuits does not affect the power to that circuit.

A business (mine included) hasnt got time to wait 20 mins + each time a module power supply is disconnected and reconnected. Not even considering the effect on the software with power being switched on and off quickly. How fast can you say corruption and reprogramming and well,.....cost.

Yes, I am aware he has found the circuit at fault.

Heat cameras ( infra red) are now being used as diagnostic aids to see where the heat is in a circuit or circuits. Expensive (£500 +) though they may be. TIPM ( totally integrated power modules) or intelligent fuse boxes ( chrysler especially) are good examples where heat build due to current drain deep.inside the component can be seen but not felt.
Sorry to interrupt the thread, but may help someone out in future.

Andy.


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Flat battery, v. high current drain - Fuse No. 8 under bonnet...

Post by Ducklakeview » Sat Nov 04, 2017 11:41 pm

andyfanshawe wrote: Sat Nov 04, 2017 10:48 pm



Heat cameras ( infra red) are now being used as diagnostic aids to see where the heat is in a circuit or circuits. Expensive (£500 +) though they may be. TIPM ( totally integrated power modules) or intelligent fuse boxes ( chrysler especially) are good examples where heat build due to current drain deep.inside the component can be seen but not felt.
Sorry to interrupt the thread, but may help someone out in future.

Andy.
Which is why I have a Flir One Pro, cracking piece of kit for jobs like this..

You can actually SEE what's starting the power, even in a packed fuse/relay box.

Mike

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Flat battery, v. high current drain - Fuse No. 8 under bonnet...

Post by andyfanshawe » Sun Nov 05, 2017 12:58 am

Ducklakeview wrote: Sat Nov 04, 2017 11:41 pm
andyfanshawe wrote: Sat Nov 04, 2017 10:48 pm



Heat cameras ( infra red) are now being used as diagnostic aids to see where the heat is in a circuit or circuits. Expensive (£500 +) though they may be. TIPM ( totally integrated power modules) or intelligent fuse boxes ( chrysler especially) are good examples where heat build due to current drain deep.inside the component can be seen but not felt.
Sorry to interrupt the thread, but may help someone out in future.

Andy.
Which is why I have a Flir One Pro, cracking piece of kit for jobs like this..

You can actually SEE what's starting the power, even in a packed fuse/relay box.

Mike
Sweet!!

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Flat battery, v. high current drain - Fuse No. 8 under bonnet...

Post by Newbers » Sun Nov 05, 2017 7:20 pm

All good stuff here. I pulled the fuse (No. 8) and the noise stopped. Put it back in again and it whirred back up again. I'm assuming it's the water pump (even though I can't see it). I can feel vibration in a water hose and the noise does appear to be lower front of engine.

I'd really like to get hold of a chart of those fuses to confirm but also what I really need is a wiring diagram to see the details of how it is switched i.e. where is the temperature sensor? I'm pretty certain this will be where my problem is (unless ECU is faulty).
it
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Flat battery, v. high current drain - Fuse No. 8 under bonnet...

Post by Stuartt » Sun Nov 05, 2017 8:10 pm

Ok from what I can work out, the pump has 4 wires, 12v from fuse 8, switched 12v from engine control relay via fuse 1 , earth , and a control wire from pin 26 on the ecu.
Check that fuse 1 goes dead when you switch off the ign if it does then the fault probably lies within the water pump as it appears the control module is built into it.

Hope this makes sense.

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Flat battery, v. high current drain - Fuse No. 8 under bonnet...

Post by Stuartt » Sun Nov 05, 2017 8:15 pm

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