Brake lights don't work in drive?

murcogmurcog Member Posts: 8
edited May 2015 in Buick
They work in park but not when driving.........


  • thecardoc3thecardoc3 Member Posts: 5,557
    The brake lights are controlled by the body computer based on an input from the brake pedal position sensor. You will need a scan tool that can not only display the input data but can perform bi-directional tests and command the BCM to turn on the brake lights. The next testing step will depend on what is observed with this initial check.
  • murcogmurcog Member Posts: 8
    thank you "thecardoc3", but would the lights work in park but not in drive ? looks like its going to take a bit to figure this out, your reply was enlightening though.....
  • thecardoc3thecardoc3 Member Posts: 5,557
    I.P.C.O. Which stands for Inputs, Processing, Communication, and Output. Don't be over concerned with the operation of the lamps depending on the gear that is selected beyond allowing that information to let a tech reproduce the issue so that the system can be tested and prove what is happening while it is occurring..
  • murcogmurcog Member Posts: 8
    Thank you for taking the time to help. I am an old school mechanic and have a bit to learn,,,,
  • thecardoc3thecardoc3 Member Posts: 5,557
    edited May 2015
    With all of the different systems out there and as fast as everything changes, everyone has more things that they have not seen out there than they probably even care to know about. We always used to preach the basics. Today the basics demand that a technician start with a scan tool that fully supports the system that is presenting with a symptom. Then it's off to service information for code descriptions (if there were any), a schematic, and a system operation and description so that he/she knows which modules are involved in accomplishing any given task. Then the technician can start figuring out what their own diagnostic routine will be, provided they have the tools and skills (digital oscilloscope, current probes, in some cases pressure transducers and more). If someone doesn't have this kind of ability then they are forced to have to try and follow trouble trees written by the OEM. The problem with doing that is many of the trouble trees only concentrate on testing for shorts, grounds, or opens which gets very labor intensive and often fails to lead to the problem.
  • newguy77newguy77 Member Posts: 1
    My ford focus had this issue where the brakes worked in park but not drive. When stopped for gas, i boticed my rear light housing was super hot. The dealer found out my gear shifting control box blew out and happened to be because uhaul installed the tow hitch and wiring and the dealer and Sears said the wiring was so shady and it caused my cruise control to not work.

    The problem was that the brakes were Always ON so the gear shifting control blew after uhaul installed, cruise control wouldnt work because it only works if brakes are off. 

    Cost me almost $700 to fix. When i tried to confront uhaul after immediately noticing my cruise control didnt work after their work, they said its not us. So theres no way to prove and is always the case. My advice is never get a tow hitch wiring job from uhaul.
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