05 Audi A4 Brake Light Switch DTC 526

Alex Technician Denver, Colorado Posted   Latest   Edited  
Question
Electrical
2005 Audi A4 2.0L (F BPG) 6-spd (01X)—WAUDF78E55A527572
00526
Brake Light Switch

I have a DTC 526 brake light switch circuit open. I tested the old brake light switch and found it was not switching the 12 volts from fuse 282 to 0 volts on pin 2 of the brake light switch connector when the brake pedal was depressed. The brake lights stay on at all times. I replaced the brake light switch and the brake lights are still staying on whenever the key is on or engine running. 

I rechecked the circuits and all relevant fuses are good and I have 12 volts on pins 1, 2, and 3 with the brake pedal released. When the brake pedal is depressed, now pin 2 (white/red) goes to 0v as it should. 

The problem is I have 8 volts on pin 4 (red/black) with the pedal released, and it goes to 12 volts when the pedal is depressed. If I disconnect the electrical connector from the brake light switch, the red/black wire has 8 volts on it. This wire goes directly to pin 25 of the engine control module. So it appears the ECM is supplying 8 volts to this wire at all times, and when the brake pedal is depressed this wire goes to 12 volts from fuse 14.

My question is, shouldn't this red/black wire to ECM pin 25 have 0 volts with the brake pedal released, and 12 volts with the pedal depressed? Ive inspected the wiring all the way to the ECM and there doesn't seem to be a short to voltage anywhere. I haven't inspected the electrical connector at the ECM yet because I'd have to drill rivets on the connector bracket to do that. Any help will be much appreciated.

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Obie Technician
Spokane, Washington
Obie Default
 

There is a procedure to install those switches. If not correctly done the brake lights will stay on. Check the installation and if the switch is aftermarket get an OE and try again.

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Justin Technician
Concord, California
Justin Default
 

My first thought was to check how you installed it (make sure adjusted proper) then maybe check to see if a tail lamp filament is shorted to brake lamp circuit

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Victor Owner/Technician
Doral, Florida
Victor Default
 

Check for shorted wiring or incorrect bulb.

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Bill Owner/Technician
Jackson, Michigan
Bill Default
 

Possible switch instillation error (reference service info for switch install) or shorted/incorrect bulbs

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Alex Technician
Denver, Colorado
Alex Resolution
   

Thanks to all who replied. I checked pin 15 of T32B at the vehicle electrical system control module and found 0 volts when I should have been seeing the same reading I had at the brake switch connector. I found the red/black wire broken about 6 inches away from T32B. This red/black wire from the brake switch splits and goes to the electrical system module and the ECM. The 8 volts I was seeing…

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