P0504 intermittent brake switch short circuit problem

[Robert Sutherland]

I've got a real puzzler on my hands and I'm hoping someone has an answer.

The brake light control circuit on my Liberty (2006 CRD Limited W/235000Km) trips its fuse at completely random intervals ( hours or even days apart) killing the brake lights and sending the code P0504. I suspect a grounded wire somewhere in the harness, but cannot find where it would be, nor does any bumping, shaking or pulling of the wiring seem to replicate the conditions of the fault.

Would the brake switch be capable of causing this condition? There is also a relay tied into this circuit in the rear of the vehicle, could that be the cause?

I've temporarily cut out the factory trailer wiring harness to eliminate it as a cause (it was the most likely culprit)

 

[Billwill]

Wise move to disconnect the trailer harness although the factory fitted one is generaly good.....after market trailer harness tend to give problems.

What fuse is blowing?...I can look it up in the logics.

The 2006 Jeep KJ Service Manual states: P0504 as being Brake Switch Signal Circuit Plausability With Redundant Contact page 9-1003. However not unusualy page 9-1003 is all about oil pressure sensor...lots of errors in the wiring diagrams and I am not prepared to leaf through every page to find the actual one for this error!

The code is probably created after the fuse has blown.
Pluasability error usually refers to the relationship between the brake switch itself and the switch inside the Brake Reservoir.....lets first trace the blowing fuse problem!

The 2006 LHD CRD has a known problem of the Fuel Filter Head Mounting Bracket damaging the wire harness going behind it. Remove this bracket and check the wiring there for chaffing to chassis or shorting between wires.

2006 Jeep KJ Service Manual: www.colorado4wheel.com/manuals/Jeep/KJ/

 

[Robert Sutherland]

the fuse that is currently blowing is #12 in the panel inside the cab on the drivers' side, the owners manual lists it as the stoplight circuit. I was able to find a wear spot on a solid red wire behind the fuel filter head mounting bracket. Got it taped up, will it fix my problem, we will see, but it at least will prevent another one down the line. thanks for the link to the service manual, I've been looking for that

 

[Billwill]

the fuse that is currently blowing is #12 in the panel inside the cab on the drivers' side, the owners manual lists it as the stoplight circuit. I was able to find a wear spot on a solid red wire behind the fuel filter head mounting bracket. Got it taped up, will it fix my problem, we will see, but it at least will prevent another one down the line. thanks for the link to the service manual, I've been looking for that

I have never actually seen that area behind the Fuel Head Mounting bracket..just repeating what is a known problem. I think that some form of "padding" should be fitted in that area to prevent the cabling being forced against the firewall causing damage in future!