Desperately looking for a fix for this code. P0504, 2005 jeep liberty crd with GDE full torque eco tune.

Changed out brake switch at the pedal, problem is still there = no brake lights, or cruise control, shake at idle during warmup.

I did recently drive across the country and was above 10k feet but have since dropped below 5k feet to sea level. I have seen elsewhere that there is a tsb for a reflash to correct the error.

Was told there is another switch in the engine compartment by the master cylinder but cannot find it or a part for it anywhere on the internet to replace.

Although there are other topics on this problem within the forum I have not found anyone who has had a definitive solution to the problem. If I get the new flash update will i lose my GDE full torque tune? Can anyone point me to the pressure switch on the booster under the hood of the car? Has anyone fully solved this issue?

Thanks,

Dan

The 06 FSM, you can get a copy from the link in Sir Sam's NOOB guide, says that code is P0504-BRAKE SWITCH SIGNAL CIRCUITS PLAUSIBILITY WITH REDUNDANT CONTACT and suggests some things to look at.

Comments:
1. I doubt it's the ECU as that's a pretty "robust" unit. However if you get a reflash from a dealer you will lose your GDE tune but GDE only charges $50 to reflash the tune. On the other hand if it comes to needing a flash Keith at GDE may be able to do it for $50
2. cannot help you with the switches but with cruise out I wonder about your wheel speed sensors particularly the one on top of the rear differential as the wires to that are well know to be weak and to break inside the insulation.
3. shake at idle is likely unrelated, check air in fuel filter head, consider motor mount(s) and maybe tranny mount. Does shake at idle go away when engine is warm? If so is there any difference between cold and warm idle rpm? I have no clue how a diesel handles holding a smooth idle on a cold engine but if the problem is limited to a cold engine then that's where to look.
4. my reasonably comprehensive TSB list doesn't show anything related to this.
5. as far as I know the gasser and CRD brake systems are the same. If so a really good brake shop might could help with the code issue.

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Sold to LOST member my 05 Ltd, GDE Stg II turbo + TCM tune, SunCoast TC w. Transgo kit, Steiger window regulators, Samcos, Fumoto valve, 2nd gen filter head with Lub. Spec. bleeder, Hayden clutch & 11 blade fan, inverted spare, P-1 battery, BF Goodrich Long Trail TAs, Etecno1 glow plugs, timing belt at 50K miles/8 yrs

So far problem solved for P0504 error code = No brake lights and no Cruise Control. Here are the steps I took.

1. Delete Error code = no solution

2. Replace brake switch located by brake pedal = no solution

3. Load old stock tune = no solution

4. Reload GDE Full Torque Eco Tune = No solution

5. Check fuse box for stop lights (Fuse #12 I believe) 10amp blue = Solution! Fuse was blown, replaced, deleted code and drove for 20 minutes with no further issues.

Will confirm tomorrow when driving to work that this has fully fixed the problem. Thank you for the reply papaindigo! A very Occam's razor type of solution.