[s-cars] Battery Drain Found & Fixed

Fred Munro munrof at sympatico.ca
Sun Apr 18 20:10:47 EDT 2004

Thanks to Tom, Igor, Teddy, Calvin, and Dave for responding to my current
drain question and confirming that the drain was indeed too high.

A bit of work with a digital ammeter isolated the problem to the automatic
window closure circuit. Pulling the A1 breaker in the under-hood relay box
dropped the drain to below 10 mA.

This circuit is designed to close windows or the sunroof if they are open
when the car is locked. This feature has never worked on my car. The circuit
has it's own relay under the driver's side A-pillar kick panel. The power
supply side is "fused" with a 30 amp breaker in the A1 position in the
underhood relay box. The relay is triggered by a white/yellow wire from the
power window control module.

This is apparently a relatively common source of a battery drain problem -
it is written up on Scott Mockry's website and the recommended fix is to cut
the yellow/white wire.

Removing the A1 breaker fixed my problem - this disables the auto close
circuit and leaves the power windows operational. From this I assume my
relay is either fused closed or is indeed being activated by the control
module (via the yellow/white wire) and the power drain is in the circuit
itself somewhere.

The car now has a 100 mA drain for 30 seconds after the alarm is set, then
it drops off to 10 mA with a spike to 20 mA every 5 seconds.

A substantial improvement from 280 mA.

When I get some time (ha!) I'll pull the relay to check it out.

Fred Munro
'94 S4

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