06 CRD P0504 fault code help

Steve777 · **Joined:** Fri Oct 16, 2015 11:31 pm **Posts:** 286

Been dealing with a P0504 code, stop light switch redundant circuit mismatch, for a while now without much luck. I am not exactly new to this code, have had it pop up now and again on other CRDs, but it was never this this hard to track down and solve. I have tried several things only to have the code come back, usually fairly quickly (like within 10 mi of driving). I have read many posts on this problem but have not yet come up with the solution. Here is what I have tested/tried/done so far, in case something jumps out at someone:

1. All the brake light work fine, did from the beginning.
2. Checked fuse #12, it is fine.
3. Replaced the stop light fuse (aftermarket).

None of these things pointed to any problem, and the new stop switch did not change anything.

When I look at the code on my reader, it typically records the stats of when the error happened, and it usually is at 0 MPH, so stopped (likely at a light). Not sure what if anything this may mean.

Have looked in the 06 Service Manual, pg 9-990 for the diagnostic steps for this code, and unfortunately they assume you have a dealer code reader to check a bunch of stuff, so not able to get too far with this. When the weather improves (around 0F now) I could check the simple voltages and for shorts there, but given all the stop lights are working and bright I'd expect those to be in good shape.

Thought I should unplug and check the main computers connector for that pin, but it isn't loose so unlikely to be the problem, but suppose it could have some corrosion.

Bad replacement switch? Maybe, but I have used this brand before and they were fine.

Looking for ideas of what to check next. Does the error happening at 0mph give any clues?

WWDiesel · **Posted:** Sun Nov 30, 2025 2:02 pm

P0504 -- Brake switch – A/B correlation Wiring, mechanical fault

Found this, maybe it can be of help in finding your problem? The item below (**) in bold red text is most likely key to the problem.
HINT: I would also check all voltages, fuses, signals, grounds, etc... at their respective locations with a voltmeter, while operating the brake pedal to ensure they are providing the ECM with the correct signal for their respective positions.

Quote:

The P0504 code means there's a correlation fault between the two signals from the vehicle's brake switch, indicating a problem with the switch, its wiring, or the brake pedal adjustment. This can cause symptoms like a check engine light, non-functional cruise control, and incorrect brake light operation.
**The underlying issue is that the vehicle's computer (PCM) receives contradictory signals that the brake pedal is both pressed and released at the same time.

Causes of a P0504 code
Faulty brake light switch: The switch itself may be damaged or malfunctioning, leading to incorrect signal output.
Brake pedal adjustment: If the brake pedal is out of adjustment, it can prevent the switch from functioning correctly.
Wiring issues: A short circuit, open circuit, or damaged wiring harness connected to the brake switch can cause an improper signal.
Blown fuse: A blown brake light fuse can interrupt the circuit and cause this code.
Mechanical obstruction: Debris or dirt can physically prevent the brake switch from operating properly.
You can watch this video to learn how to diagnose and fix P0504 code:

Quote:

How to diagnose and fix

Steve777 · **Joined:** Fri Oct 16, 2015 11:31 pm **Posts:** 286

It's been a while, but I am finally getting back to this P0504 code. It's been a long, winding road, with several dead ends. I think I have made some progress, but need some advice and maybe part numbers from the folks here.

A.First prob was that aftermarket brake lite switch from Amazon. It was a dud, but I did not realize it for a while.

B. I took part the rear tail light assemblies and found the two top bulb holders burned and melted. Had the right bulb in it, so I ordered some replacements. After a bit of testing, found out those new bulb holders were nice and shiny but did not work (from Amazon again, I must be a slow learner ;-)

C. Put the old bulb holders back in the top positions, and at least I have top stop lites now.

The P0504 code seems to be gone for now, but I have not driven that any miles, so we'll see. But whether it returns or not I still have work to do on these rear lites, and I have questions about how things are supposed to be (can't trust that the parts I took out are the right ones in the right place). So here goes:

1. What is the Mopar part number for the 3 prong bulb holder (or a good aftermarket one). The working one I have has a 6100 printed on it.

2. What is the right Mopar (or good aftermarket) partno for the 2 prong bulb holder? The working one has a 6094 on it.

3. This may sound strange, but I am not familiar with how these rear lite bulbs are supposed to work (which come on for what).
a. Can someone pls tell me how many bulbs are supposed to come on when you press on the brake pedal? Which ones?
b. Turn signals are the yellow bulb at the upper clear part, which work.
c. Where are the backup lites supposed to come on (I think I am not getting them cause I don't have the lowest bulbs in)?
d.When do the lower bulbs on each side come on?

4. I am puzzled by the bulb sockets this Lib came with. Top one has 3 prongs and has contacts for all 3 prongs, so that's OK. The bottom bulb holder came with 3 prongs, BUT the hole it goes into only has 2 contacts. Should I be getting a 2 prong bulb holder for this position?

5. And can someone point me to the page in the FSM where it spells out which bulbs are the right ones in these rear lites.

Lots of questions, but thanks in advance for reading and any answers.

WWDiesel · **Posted:** Fri Jul 03, 2026 1:47 am

I'll try and help with what I can find. If I list anything wrong, I am sorry, I tried and it gets quite confusing on this item with so many different options and export models thrown in the mix. (Bulb Sockets)

Did a enhanced drawing of the tail lights showing the wiring to the bulbs.
It only shows three bulbs per side, one turn signal, one brake light, and one backup light. All of them have only TWO contacts, not three according to the wiring diagram. See drawing.

According to what I could find on the Mopar online sites, the 05 & 06 Liberty's used the three bulb socket lights (listed below).
Models using the four bulb socket lamp assemblies were for Fog lamps (Export). 55155830AH & 55155831AH

These are the part numbers I came up with for bulb sockets:
4676589 Mopar (Stop Light)
55157302AA Mopar (Turn Sig.)

Your best option is to purchase both new tail light assemblies, they come with the bulb sockets new.
These are the part numbers for the 3 bulb housing assemblies.
Rear Tail Light Housing Right -- 55157060AG
Rear Tail Light Housing Left -- 55157061AG
Google the part numbers, there are plenty of them available online, ebay, amazon, and others....

I replaced both of my tail light assemblies a few years ago due to bulbs not wanting to work at times. So I ordered complete assemblies and replaced both of them. I think I ordered them off eBay???

Steve777 · **Joined:** Fri Oct 16, 2015 11:31 pm **Posts:** 286

Thanks WW. Replacing the whole units is probably easier than trouble shooting alll these possibilities.

That diagram is quite useful, in that it shows the top center stop light just wired in parallel to the lower units. Since that lite wlways came it it shows the stop switch and wiring are working (which is a relief).

Thanks again, and have a good 4th.

06 CRD P0504 fault code help

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