Car battery goes flat overnight
Posted: Wed Dec 21, 2016 12:06 pm
Car battery goes flat overnight. No obvious hot spot to explain where the power went. Amp meter in battery lead shows a constant drain of about 1 Amp this damages modern lead acid batteries. You may need to replace battery soon.
Other symptom: Windows may occasionally close unexpectedly whilst driving.
Cause: Power Windows sub-system is not going to sleep after 5 seconds of inactivity.
Test: remove power window fuse in fuse box by driver's right knee.
Probably root cause: 'All windows up' switch attached to passenger side door key lock is still active when key is in the near vertical position at which it can be removed.
Solution: remove lock and adjust operating angles of this switch.
Background: Each door has its own windows control computer that goes to sleep when there is no activity. The 'all windows up' signal is a low priority command that is ignored once window is up but if it persists prevents computer from going to sleep resulting in a power drain. A 1 Amp drain that persists overnight causes permanent damage to modern lead-acid starter batteries. Professional battery test will show battery capacity has dropped to about 8 AmpHrs from the 40 or so of a new battery.
Fault can be intermittent depending on how you turn and remove door key.
Applies to cars with central locking and power windows.
Other symptom: Windows may occasionally close unexpectedly whilst driving.
Cause: Power Windows sub-system is not going to sleep after 5 seconds of inactivity.
Test: remove power window fuse in fuse box by driver's right knee.
Probably root cause: 'All windows up' switch attached to passenger side door key lock is still active when key is in the near vertical position at which it can be removed.
Solution: remove lock and adjust operating angles of this switch.
Background: Each door has its own windows control computer that goes to sleep when there is no activity. The 'all windows up' signal is a low priority command that is ignored once window is up but if it persists prevents computer from going to sleep resulting in a power drain. A 1 Amp drain that persists overnight causes permanent damage to modern lead-acid starter batteries. Professional battery test will show battery capacity has dropped to about 8 AmpHrs from the 40 or so of a new battery.
Fault can be intermittent depending on how you turn and remove door key.
Applies to cars with central locking and power windows.