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991 High Lvl Brake light inop

deMort

Monaco
Joined
21 Mar 2015
Messages
11,242
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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