Hi all, My 1999 75 is suffering from a parasitic battery drain which appears to be coming from the BCU (Body Control Unit). After letting the car 'go to sleep' I have a 100ma battery drain - the only fuse with any drain across it is #5 which according to my manual only feeds the BCU. Does anyone have any experience of this? I'm wondering if it's likely to be the BCU that's faulty or an input to the BCU that's causing the issue. The car doesn't have any electrical gremlins / everything works as it should and the original Rover radio / sat nav system is completely disconnected. Any advice appreciated. Thanks
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Battery Drain by Daveyk1976
With searching the web for electrical issues a parasitic drain seems like a common issue with Rover 75s and I have a reading of 0.69 drain on the 10amp setting. Some suggest that Rover 75s can get wires near the boot light damaged to cause a drain. I found my boot light stays on. Web says others find the switch on the rear boot/tailgate lock goes wrong to tell the car that the boot/tailgate is not closed. Some on the web take many fuses out to check
To give a clue what kind of things you could both be looking for. 100mA is 1.2Watts, so unlikely a bulb. 690mA is 8W so could be an interior light of which there are many to choose from. If the car thinks a door, boot or bonnet is open, it tells you in the instrument panel, and will beep when you try to lock it.
By common sense it seems my Rover 75 CDTi saloon is not going to sleep to cause the parasitic drain. Or I suppose one module is not going to sleep? - I just did a parasitic drain test with the car in use but the engine switched off and key off and doors unlocked. The reading is exactly the same (around 0.69 on the 10amp setting) as when I wait an hour with the car locked and bonnet switch held down.
It is a recognised potential fault on web searches that a module does not go to sleep.
It is a recognised potential fault on web searches that a module does not go to sleep.
With the way it works, any module not sleeping, could cause the whole car to stay awake. To look into whether something is keeping modules awake, it might be worth looking at the KBus. You don't need anything complicated, your multimeter will do.
Set it to DC voltage, on a range that will cover up to 12v. On most meters, the 20v range. Connect the red to a KBus connection, black to ground. KBus is the White / Red / Yellow wire that connects to many ECUs on the car. Behind the radio might be the easiest.
When the KBus is active, it is constantly switching between 12v and 0v, very fast (actually around 9600 times a second). Your multimeter isn't fast enough to show this BUT will generally show a varying voltage, sitting at 6-7 volts but certainly lower than battery volts (12v). When the KBus goes to sleep, it sits at 12v all the time, which your meter would show. There are tools (oscilloscopes) that can show you exactly what is happening, and they are cheap enough, but overkill when your multimeter will show enough.
Set it to DC voltage, on a range that will cover up to 12v. On most meters, the 20v range. Connect the red to a KBus connection, black to ground. KBus is the White / Red / Yellow wire that connects to many ECUs on the car. Behind the radio might be the easiest.
When the KBus is active, it is constantly switching between 12v and 0v, very fast (actually around 9600 times a second). Your multimeter isn't fast enough to show this BUT will generally show a varying voltage, sitting at 6-7 volts but certainly lower than battery volts (12v). When the KBus goes to sleep, it sits at 12v all the time, which your meter would show. There are tools (oscilloscopes) that can show you exactly what is happening, and they are cheap enough, but overkill when your multimeter will show enough.
Oh, and does your car have an FBH (Fuel burning heater.)? They can be real problem causers when it comes to KBus.