Rear win­dow op­er­a­tion

Car Mechanics (UK) - - Help! -

The rear win­dow demis­ter is not work­ing on my wife’s 2000 BMW 320i. There is power to the main feed wire to the re­lay, power to the blue wire and power to the blue/red wire (about 6V), but I do not think power should be in the last of these as I be­lieve it to be ground. The black wire has no power to feed the grid on the win­dow.

I put in a brand new BMW re­lay to no ef­fect. I won­der if you can shed any more light on where the fault could lie? Chris Barrett I am as­sum­ing that this is a sa­loon and not the Tourer ver­sion. If you do have the Tourer with an open­ing rear glass, then the prob­lem is of­ten a fail­ure of the wiring within the hinge.

Ac­cord­ing to the wiring di­a­gram I have, your HRW is con­nected to an an­tenna mod­ule via four wires, which ap­pear from my data to all be black. The con­nec­tions to the an­tenna do suf­fer from cor­ro­sion and this nor­mally re­sults in poor ra­dio re­cep­tion. I would start by check­ing the wiring from the an­tenna unit, which is lo­cated in the rear quar­ter panel be­hind the trim.

An­other com­mon fail­ure on the 320 is the el­e­ment within the glass, which would in­volve fit­ting a new win­dow. In ad­di­tion to this, the sys­tem is op­er­ated via a con­trol unit and prob­lems with the screen can be the re­sult of a failed con­trol unit or a faulty al­ter­na­tor, among other things. If there are no phys­i­cal signs of elec­tri­cal fail­ure, it may pay to get the sys­tem checked by a ded­i­cated BMW sys­tem to pin­point the prob­lem – this could save hours of di­ag­nos­tic time.

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