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RhoXS 07-29-2013 04:10 AM

Rear Defogger - Time Delay off
To my surprise, I noticed the rear defogger auto turns off after exactly ten minutes. Preferably, I would like to eliminate any auto off time delay so it stays on until manually turned off or the car shut down. Alternately, I would like to extend the time delay to something much longer than ten minutes. Can either of these changes be made by the dealer or coding?

On warm humid days the rear window fogs up when the defogger is not on. On cold winter snowy days it helps considerably leaving it on continuously. So it is a pain every ten minutes to notice it fogs up or start collecting ice/slush then turn it back on. If the time delay is the result of an efficiency thing it is really meaningless. The circuit is fused at 15 amps. Assuming worst case 15 amps of current, that is less than 1/4 HP. I could afford the BMW so I certainly can afford the miniscule amount of additional gas leaving it on continuously will burn.

The X Men 07-29-2013 04:21 AM

Why don't you just turn on the AC on humid days?

RhoXS 07-29-2013 05:09 AM


Originally Posted by The X Men (Post 7738880)
Why don't you just turn on the AC on humid days?

Using the A/C is exactly why the rear window fogs up.

The A/C lowers the temperature of the glass below the dew point for the conditions outside the car. The fogging occurs on the outside of the glass, not the inside. The rear defogger raises the temperature of the glass slightly, to just above the dew point so no moisture condenses out on its surface. This is the same phenomena that causes water to condense out on the outside surface of a glass of ice water.

The X Men 07-29-2013 05:31 AM


Originally Posted by RhoXS (Post 7738908)
The fogging occurs on the outside of the glass,

I use the rear wiper for that problem.

mpabner 07-29-2013 07:44 AM

Rear Defogger - Time Delay off
Here in FL, the wiper helps for approximately 5 seconds, then re-fogged. Continuous defogging would be much appreciated.

Sent from BimmerApp mobile app

The X Men 07-29-2013 08:03 AM

Must be a Florida thing, I don't have that problem up here in the north east.

RhoXS 07-29-2013 08:43 AM

I am just north of Syracuse and this is where my X3 will live for the next few years even though my home is in Florida. Yesterday was a warm humid rainy day and the rear window fogged up immediately after a blade swipe if the rear defogger was not on. I also noticed this past winter (in my Lexus SUV that is shortly heading back to Florida) slush and ice built up quickly on the rear window on cold crappy days while traveling at interstate speeds. If the rear defogger was adding heat visibility remained much better between blade swipes.

Anyway, my question was not to debate the merits of using the rear defogger but only to find out if the time delay to off is a programmable parameter. I either want the dealer to reprogram it if it is or, if the dealer won't, code it myself.

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