Break lights/cold weather battery failure

SWEETBABY9

MEMBER
SUBARU

My car is a Subaru Legacy LSI - 1995 with 138,000 miles. Over the past four years whenever the temp. Outside drops below 20 degrees the cars battery is dead in the mornimg. I have had the alternater replaced as well as three new Subaru batteries. Two seperate dealerships can't explain what the problem is. Today I went out at 5:00 am to see if it would start (5 degree morning). I found the brake lights on. The car had a VERY hard start. Is this always happening in very cold weather? Is this what is draining the battery? FYI, I have had to have the ABS pump replaced twice on this car. Could there be a link?

1 Reply

BRENDONR

MEMBER
22 POSTS

This recently happened to me in my '92 Legacy.

Here's what I found.

I talked to a mechanic at my local Subaru dealer - he said that in super cold weather (Calgary Canada - we were seeing 30 below zero overnight.) There's a small amount of compression in your brake fluid, enough to let your brake pedal fall a small amount, and make contact with your brake light sensor. He suggested bringing my car in, and they could 'turn down' the sensitivity on the sensor.

However upon a little more investigation, I found that my aftermarket alarm/keyless entry unit was installed poorly. It was stuck onto my ECU with. Drumroll please.

DOUBLE SIDED TAPE!

So when the weather got stupid cold the tape froze, and the control unit for my alarm popped off the ECU (or what i'm assuming is my ECU), it then was pushing on my brake light sensor hard enough to turn the lights on in the cold.

Hope that helps.