MJJ
Active Member
- Joined
- Jan 13, 2020
- Messages
- 135
- Location
- Wiltshire
- Car
- '09 S211 E220 CDi manual - 197k miles and counting
Afternoon all,
I have recently chased, and solved a current drain on my 2009 S211 E220. As it was a right pain to find, I thought it may help to document it - might be useful for others.
I only noticed the drain problem as we entered lockdown, and the car stopped being used very often. After 4 or 5 days, the battery had reached 10V and the car would not start. The usual method of diagnosis - multimeter inserted in series with the battery +ve wire, and I traced the drain of around 160mA to fuse 9 in the boot. This is the overhead control panel (i.e. interior light panel, front).
The useful WIS section on "quiescent current" tells me that a drain of that magnitude is likely a CAN module staying awake - i.e. the OCP module was not sleeping after the car was locked. The attached image from WIS shows what the current profile should look like as the car goes to sleep, post locking. Mine now only uses 35-40mA after 6 or so minutes.
After much diagnosis and a helpful post on a US forum, it transpired that a tired alarm siren (behind the front wing wheelarch liner, OSF on facelift, NSF on pre-facelift) was stopping the OCP module sleeping. My best guess is that the internal battery in the alarm siren fails over time, and thus always demands a charge from the car - this somehow keeps the OCP awake, probably because the "interior sensor disable" button is in the OCP.
Anyway, alarm siren removed, current drain gone. No adverse effects so far, though if anyone tries to steal the car by cutting the main battery lead, then there will be no siren sounding. I can live with that. A new alarm siren appears to be around £120, but I don't see the need to replace it, personally.
Martin.
I have recently chased, and solved a current drain on my 2009 S211 E220. As it was a right pain to find, I thought it may help to document it - might be useful for others.
I only noticed the drain problem as we entered lockdown, and the car stopped being used very often. After 4 or 5 days, the battery had reached 10V and the car would not start. The usual method of diagnosis - multimeter inserted in series with the battery +ve wire, and I traced the drain of around 160mA to fuse 9 in the boot. This is the overhead control panel (i.e. interior light panel, front).
The useful WIS section on "quiescent current" tells me that a drain of that magnitude is likely a CAN module staying awake - i.e. the OCP module was not sleeping after the car was locked. The attached image from WIS shows what the current profile should look like as the car goes to sleep, post locking. Mine now only uses 35-40mA after 6 or so minutes.
After much diagnosis and a helpful post on a US forum, it transpired that a tired alarm siren (behind the front wing wheelarch liner, OSF on facelift, NSF on pre-facelift) was stopping the OCP module sleeping. My best guess is that the internal battery in the alarm siren fails over time, and thus always demands a charge from the car - this somehow keeps the OCP awake, probably because the "interior sensor disable" button is in the OCP.
Anyway, alarm siren removed, current drain gone. No adverse effects so far, though if anyone tries to steal the car by cutting the main battery lead, then there will be no siren sounding. I can live with that. A new alarm siren appears to be around £120, but I don't see the need to replace it, personally.
Martin.
