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Re: EDU again, and rear defogger Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Tue, 27 Nov 2007 04:51:36
In Reply to: EDU again, and rear defogger, TML   [Profile/Gallery]
, Mon, 26 Nov 2007 18:53:42
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A quick trip to an autoparts store will show defoggers can fail. There you'll find conductive paint to bridge breaks in the elements. The heating elements are just lines of resistive material painted on the glass, susceptible to damage from closing the hatch on something big, flying object, age. Also, it can be in the wiring or connections between the rear heating element and the controller. The light is in paralell with the heater, so when it comes on, it means that power is there, at least at the front of the car. There are two metal clips right on the window - measure across them with a voltmeter when the defogger is on. If you see 12 volts across the clips, there is a break in the heating elements.
If you see much less than 12 volts - 5 or 3 or near zero, measure from each clip to a good ground - a bare screw head on the chassis. If both clips measure around 12 volts, then you have a bad ground. If both clips measure much less than 12 volts - like nothing - then there is a wiring problem between the controller and the heating element.
Do your mirrors defog? They are on the same circuit. Again, that doesn't troubleshoot much of the wiring.
The ground on a hatchback is right on the tailgate, which brings us to:
Rear light out indication. Most likely a bad ground. May even be the same ground as the one causing the defogger not to work. But don't count on it.
I would pop the rear covers off each of the tail-lights, and (1) check that each bulb is correct, per the manual. The wrong bulb type can cause this problem. Are you the original owner? Do you know if a previous owner stuck the wrong bulb in? (wattage, number of filaments, etc.) (2) trace the grounds (black wire going to a bolt on the chassis) - remove the bolts, brighten up the lug and chassis metal with some sandpaper or Scotchbright, and tighten back down. Don't forget the high mounted stop light.
The fact that this problem shows up with the headlights off (but I assume the daytime running lights on) points to a bad ground.
I would first check the bulbs and then clean up the grounds. I'll bet that also fixes the defogger.
posted by 192.249....
, Mon, 26 Nov 2007 18:53:42, Tue, 27 Nov 2007 04:51:36 <-- Viewing This Message, Tue, 27 Nov 2007 09:51:15, Tue, 27 Nov 2007 09:14:38
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