Parasitic battery drain Rover 75

[Tony jr]

I’m struggling to identify a parasitic current that is draining the battery in about 3 days. I have put a clamp meter on the battery leads and measured a 1.15amp drain at rest with everything turned off. This appears to be from a fused circuit and not from the alternator as far as I can tell. I have systematically removed all of the fuses in the engine bay fuse box and then in the passenger compartment fuse box. The only fuse in the engine bay that dropped the current was the fused link 3 which I assume feeds the passenger compartment fuse box. Pulling the fuse for the radio reduces the current draw down to 0.52 amps. This suggests that the aftermarket radio radio is not shutting down properly. However this only represents half of the parasitic drain. I then pulled all of the remaining fuses and got either no change in current or minor drop with the alarm and window fuses but neither dropped the current significantly. Pulling the fuel pump fuse gave an unusual response, causing the leakage current to actually increase from the 0.52 amps up to 1.78amps. So, with the fuse removed the current draw increased! Any thoughts why this would be the case? Any ideas welcome.

[MSS]

The systems in the car do not all shut down instantaneously. Have a look at my thread here.

https://www.the75andztclub.co.uk/for...d.php?t=315487

If shutting off a system by pulling the fuse wakes up another system the overall current consumption could increase.

You need to take a planned, systematic approach when searching for the source of current drain.

[Tony jr]

I did put a steel bar on the bonnet switch and leave the car 30 minutes to fully shut down but still had the 0.51amp drain which is 10 times what I was expecting.

[Jamiewelch]

Originally Posted by Tony jr

I did put a steel bar on the bonnet switch and leave the car 30 minutes to fully shut down but still had the 0.51amp drain which is 10 times what I was expecting.

Leave the passenger door open so you can get to the fusebox and the bonnet open, once the car has settled down to the 0.51 amps, start pulling fuses one at a time until it drops.

[Tony jr]

That’s essentially what I did do. When I got the current draw down to 0.51 amps I left the car 30 min to completely shut down and measured the current again at 0.51 amps. I then repeated pulling the fuses and got the same response. Every time I pulled the fuel pump fuse the current jumped to 1.78amps. Replacing the fuse instantly dropped the current back down to 0.51 amps. I repeated this several time with the same response. If it was something else waking up when I pulled the fuse I would expect the current to say at that value for a while and not drop instantly when the fuse was put back.

[dave lincs]

Tony

If you are stuck with this I'm not far from you I'm sure we can sort it as I have all wiring diagrams and plenty of parts if needed

Dave

[SD1too]

Originally Posted by MSS

If shutting off a system by pulling the fuse wakes up another system the overall current consumption could increase.

Hi Tony,

I've looked at the wiring diagram for your diesel. When you remove fuse 28 to the fuel pumps the BCU and ECM will be woken up. This probably explains the increased current you're experiencing.

Simon

[Tony jr]

Originally Posted by SD1too

Hi Tony,

I've looked at the wiring diagram for your diesel. When you remove fuse 28 to the fuel pumps the BCU and ECM will be woken up. This probably explains the increased current you're experiencing.

Simon

Hi Simon,

I understand what you and MSS are saying about waking up the ecm and BCU when you pull the fuse and how this might explain the additional current draw. However, I would have thought that once they had woken up they would stay that way for the next 20 minutes before going back to sleep. Therefore, I would expect the increased current to stay for 20 minutes after I put the fuse back and not drop back again instantly. Is my logic misplaced? Does the ecm and bcu shut down quickly? Is it worth pulling the fuse, measuring the increased current, leaving it 30 minutes and see if the current drops back down. What effect would a faulty fuel pump relay have?

Thanks to all of you trying to help I don’t want to sound ungrateful. I’m just frustrated with it. The car runs well other than this problem.

[MSS]

Originally Posted by Tony jr

Hi Simon,

I understand what you and MSS are saying about waking up the ecm and BCU when you pull the fuse and how this might explain the additional current draw. However, I would have thought that once they had woken up they would stay that way for the next 20 minutes before going back to sleep. Therefore, I would expect the increased current to stay for 20 minutes after I put the fuse back and not drop back again instantly. Is my logic misplaced? Does the ecm and bcu shut down quickly? Is it worth pulling the fuse, measuring the increased current, leaving it 30 minutes and see if the current drops back down. What effect would a faulty fuel pump relay have?

Thanks to all of you trying to help I don’t want to sound ungrateful. I’m just frustrated with it. The car runs well other than this problem.

That's not the case. The systems shut down in stages. If you look at my measurements vs time in the link above, within a few seconds of locking the car the current is down to 0.3A.

[SD1too]

Originally Posted by Tony jr

... I would have thought that once they had woken up they would stay that way for the next 20 minutes before going back to sleep. Therefore, I would expect the increased current to stay for 20 minutes after I put the fuse back and not drop back again instantly. Is my logic misplaced?

Hi Tony,

I don't think any of us can accurately predict what's going to happen when an input is removed from an ECU connected to multiplex systems.

Originally Posted by Tony jr

What effect would a faulty fuel pump relay have?

To give an increased current draw the relay contacts would have to be stuck in the "made" position. This would result in the two pumps running continuously. You don't have that evidence.

I suggest that removing the fuel pumps fuse is not a useful test. Forget it and move on.

Does your car have sat. nav?

Simon