Thread: Fix for Discovery battery drain

If you use your Disco everyday: no problem.
If you live in a sunny place where temperatures will not fall under -15C: no problem.

BUT when you leave for a 2 week break you might find the battery of the Disco dead. Or when you use a Webasto heater to cope with the arctic temperatures that hit Norway for about 6 months AND make 2 short daily trips only - the battery needs all the charge it can get, no place for a nasty 300 mA constant drain.

But finally fixed it. You can read numerous treads about the well known 300 mA drain caused by the SLABS ECU. Problem is that this ECU is always connected to the battery via fuse 11 (30A) (standing in front of the fuse box check the label on the cover or count from right to left). I always wondered why the ABS modulator was making space invader sounds like woy-woy-woy-woy but this is because the SLABS ECU powers the ABS Pump/modulator. Removed the connector from the modulator, but 300 mA drain stayed. Pulled fuse 11 and bingo! drain reduced to 27 mA. You can even hear a soft click when a relay inside the SLABS ECU de-energizes.

Just imagine. The 100 Ah battery can produce (in theory) 100 Amperes for one hour. A drain of 300 mAh means it will take 333 hours before the battery is dead. However to crank a Td5 you need at least 60-80 amperes for a couple of seconds. This means that (in my case) not using the car for 2 weeks, or in harsh winter conditions like we have here with -20 C for a number of days, short trips AND the extra 300 mA drain cause problems.

To keep a long story short, pin 2 (C0504 which is the biggest connector on the ECU, 2nd seen from bulkhead) receives 12V through the ignition lock. I use this connection to energize a relay (taking the ground from pin 12 of same connector). The power supply for the SLABS ECU via fuse 11 is now running via the relay contacts to pin 1 of same connector. Meaning: no key no drain.

The Self Leveling function inside the same ECU still works, so after shutting the engine and removing the key and locking the car the ECU still lowers the rear suspension a bit as usual.

<Edit> I was wrong with the SLS statement directly above. When you come to a full stop i.e. reached your destination you have to give the SLS 10 seconds to lower the rear springs. If you stop and immediately remove the key the springs keep sittin' where they are.

This MUST be one of the reasons to keep the SLABS ECU under power at all times. But for a turbo engine it won't harm having it spin down before you remove the key, so still consider this to be a fix. </Edit>

I am now free from this annoying drain that has been there since 2004 when I bought the car. No worries about safety, the relay is an original LR item and prone to the same MTBF as all the other relays in the car, and the ECU does so many checks that any problem in the system will be detected.

Images show how easy the process is, takes about 30 minutes.

Originally Posted by dutchviking

If you use your Disco everyday: no problem.
If you live in a sunny place where temperatures will not fall under -15C: no problem.

BUT when you leave for a 2 week break you might find the battery of the Disco dead. Or when you use a Webasto heater to cope with the arctic temperatures that hit Norway for about 6 months AND make 2 short daily trips only - the battery needs all the charge it can get, no place for a nasty 300 mA constant drain.

But finally fixed it. You can read numerous treads about the well known 300 mA drain caused by the SLABS ECU. Problem is that this ECU is always connected to the battery via fuse 11 (30A) (standing in front of the fuse box check the label on the cover or count from right to left). I always wondered why the ABS modulator was making space invader sounds like woy-woy-woy-woy but this is because the SLABS ECU powers the ABS Pump/modulator. Removed the connector from the modulator, but 300 mA drain stayed. Pulled fuse 11 and bingo! drain reduced to 27 mA. You can even hear a soft click when a relay inside the SLABS ECU de-energizes.

Just imagine. The 100 Ah battery can produce (in theory) 100 Amperes for one hour. A drain of 300 mAh means it will take 333 hours before the battery is dead. However to crank a Td5 you need at least 60-80 amperes for a couple of seconds. This means that (in my case) not using the car for 2 weeks, or in harsh winter conditions like we have here with -20 C for a number of days, short trips AND the extra 300 mA drain cause problems.

To keep a long story short, pin 2 (C0504 which is the biggest connector on the ECU, 2nd seen from bulkhead) receives 12V through the ignition lock. I use this connection to energize a relay (taking the ground from pin 12 of same connector). The power supply for the SLABS ECU via fuse 11 is now running via the relay contacts to pin 1 of same connector. Meaning: no key no drain.

The Self Leveling function inside the same ECU still works, so after shutting the engine and removing the key and locking the car the ECU still lowers the rear suspension a bit as usual.

<Edit> I was wrong with the SLS statement directly above. When you come to a full stop i.e. reached your destination you have to give the SLS 10 seconds to lower the rear springs. If you stop and immediately remove the key the springs keep sittin' where they are.

This MUST be one of the reasons to keep the SLABS ECU under power at all times. But for a turbo engine it won't harm having it spin down before you remove the key, so still consider this to be a fix. </Edit>

I am now free from this annoying drain that has been there since 2004 when I bought the car. No worries about safety, the relay is an original LR item and prone to the same MTBF as all the other relays in the car, and the ECU does so many checks that any problem in the system will be detected.

Images show how easy the process is, takes about 30 minutes.

Hi Ductviking

Thanks for the fix, I did the same with my D2 V8

Question, have you had any long term issues as a result of this modification? If I am not mistaken, this modification means the ECU is disconnected form power whenever the ignition is not on?

Regards
Marius