Help please: Brake tail stop light stay on

[stcan]

Hi, 

I am having trouble with my brake tail stop light staying on all the time.

 

Looking at the schematic, looks like the fuse C F4 is feeding the CU PSM and it's re-feeding the A6 Stop light switch.  Is my PSM box broken?  Can I put a diode so that it doesn't back feed the power

 

Thanks

 

 

[Loren]

 

I would make sure it's not the fog light, also a bad headlight switch could also cause the issue.

[stcan]

Thanks Loren,

 

I will check the fog light and the headlight switch.

 

Can you explain how the stop light circuit work?  

[Loren]

The first thing I think is to make sure it is the stop light or tail light or fog light.

[stcan]

It's the stop light that's staying on all the time.  I change the stop light switch by the brake pedal, that didn't fix it.   

 

 

[stcan]

can you explain the arrow to the line in the brake pedal switch.  What does that mean.  Can you explain this schematic on how it works?

 

 

[Loren]

Pretty much the brake switch and control unit.

Assuming there are no shorts to ground it is likely the issue is in the control unit. Many times control unit issues can be fixed by re- programming that module. If that does not work then a new control unit will need to be installed and programmed to your car.

[stcan]

Thanks for your help Loren, it's the control unit.  I replaced it and problem is fixed.

 

 

[Loren]

46 minutes ago, stcan said:

Thanks for your help Loren, it's the control unit.  I replaced it and problem is fixed.

 

 

 

[stcan]

looks like there is a short in the board.  There is constant power on the brake trigger input in the box.  

 

I am wondering if that can also be software issue.  Is there a way to do factory reset on the rear module firmware?

 

Steve

[Loren]

Many times control unit issues can be fixed by re- programming that module. If that does not work then a new control unit will need to be installed and programmed to your car.