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Re: Pictogram lighting measurement question... Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Sun, 21 Dec 2008 22:34:28
In Reply to: Pictogram lighting measurement question..., vtsnaab   [Profile/Gallery]
, Sun, 21 Dec 2008 15:05:09
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It actually depends on the year. Early cars - 88 and earlier - had only one monitor, mounted in the relay box above the fuse panel. Later cars have two - one for headlights, mounted in the headlight relay box in the engine compartment (red 'relay'), and another for the rear lights, mounted by the left rear brake light cluster.
The monitor compares the current from the left and right hand bulbs, in pairs. So it compares the current through the left low beam headlight filament with the current in the right low bean headlight filament. If the currents are different, the system figures one bulb is out. Same with all the other lights - compared in pairs.
In the early cars, this was done with an actual relay with two coils - the bulb current flowed through the two coils - if the currents balanced, the relay stayed open; if the current was unbalanced, the relay closed, and lit the pictogram. The technical term for this method is a Kludged-Up Mess, and had the reliability of a 15-year old Fiat. The pictogram would light up randomly.
In later cars, Saab went to a solid-state version, that actually measured the currents and compared them. Again, very simple, but a lot more robust. Not very sophisticated - just simple analog circuitry, no microprocessors.
No, these monitors don't do anything else. The pictogram is also driven by the door ajar switches
posted by 99.159.103...
, Sun, 21 Dec 2008 15:05:09, Sun, 21 Dec 2008 22:34:28 <-- Viewing This Message
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