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991 High Lvl Brake light inop


21 Mar 2015
The spoiler brake light inop ..

The broken wire issue is pretty well known and you will get a dash warning message if this happens .

Car i've just had in had no dash warnings and was merely found to be not working on a service ..

Spoiler removed and a wiring check .. all ok .. ohms reading for the light unit being an led system was 10 K ohms which is actually correct but i powered it up out of the car and indeed it worked .

Spoiler back in the car and on a tester the car could see that the spoiler was extended but it didn't switch the center brakes lights .

No feed was found to be coming from the rear end control unit to turn on the lights when it should .. control unit issue obviously .

A little bit of thinking and i considered a coding issue perhaps , there is an option for a fixed wing on these so perhaps its coded to that ..

On these cars you cant see individual coding in each control unit but only in a master list and of course yup it was listed as a retractable spoiler ..

On a hunch i hit auto coding of the rear end control unit ( BCM rear )

Brake lights now work correctly .. somehow the control unit had decided it had a fixed wing !

best guess would be from a flat battery at some point .

Not something i've ever seen before .

In short .. spoiler brake light inop with no dash warning and have the rear cu auto coded with a tester ..

It will save you the 1.5 hrs it took me to track this one down.

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