P0504: The two brake switch signals disagree
Brake switch A/B correlation
Severity: Severity not verified — if the car runs badly, have it inspected
The two brake switches feed brake lights, cruise cancel and stability systems, but the readable sources did not rate the severity, so it is not verified.
It gets more serious if:
- Inspect soon: Get it checked promptly if the brake lights stay on or do not come on, or cruise control stops working, because brake lights warn drivers behind you.
P0504 in short
P0504 means the computer sees the two brake pedal switch signals disagree, when they should change together as you press the pedal. A faulty switch, its wiring or adjustment are the likely areas. Brake lights may not work correctly, so have it checked promptly. Severity is not verified.
Many cars use two brake switch signals that should change state together when the brake pedal moves. TaT describes P0504 as two signals that should track each other diverging beyond tolerance.
The pair is used for brake lights, cruise control cancel and input to ABS and stability control, so the fault matters for safety even though the code sits in the engine range.
Because this is the brake system, this page gives no do-it-yourself repair steps.
Most likely causes
Cause 1: Faulty brake switch or its wiring
Common general cause- Why it ranks here
- The code's definition is a disagreement between the two switch circuits, which points to the switch or its wiring, but the causes lists were not readable.
- What would change this
- Rises if brake lights stay on or fail to light. Falls if both switch signals change together on a scan tool.
Cause 2: Engine computer software (some Jeep models)
Supported by vehicle data- Why it ranks here
- A Chrysler flash bulletin covers P0504 on 2005 to 2006 Liberty and Grand Cherokee. Only its NHTSA summary was read.
- What would change this
- Rises if a dealer finds the update applies. Falls if the computer is current.
What to test first
Start at step 1. Each result tells you what it means and where to go next.
Step 1: Have a shop watch both brake switch signals on a scan tool while the pedal is pressed and released.
Warning:Brake system work is safety-critical. Let a shop do it.
IfThe two signals do not change together
It meansThe switch, its adjustment or wiring is suspect.
IfThe signals agree
It meansAsk a dealer about a software update.
Symptoms
- Check engine light on
- Brake lights stuck on or not lighting Gets more serious: stop and have it checked.
- Cruise control not working Gets more serious: stop and have it checked.
How to fix
This is a safety-critical system, so we explain the code but don't give repair steps. Have it inspected by a qualified technician.
On your vehicle
JeepYour car
2005–2006 · Liberty
Supported by vehicle dataA Chrysler flash bulletin covers brake switch DTC P0504 with an altitude drivability update on Liberty and 2006 Grand Cherokee. Only the NHTSA summary was read; whether it is still current is not verified.
2005–2006 · Liberty
Supported by vehicle dataA second Chrysler bulletin (1800906) names brake switch DTC P0504 on 2005-2006 Liberty and Grand Cherokee. Only the NHTSA summary was read; whether the bulletin is still current is not verified.
1803805Status unverified
Flash: engine start and drivability at altitude / brake switch DTC P0504
2005–2006liberty, grand-cherokee · issued · NHTSA 10018576
Software (flash) update covering starting and drivability at altitude and brake switch DTC P0504. Only the NHTSA summary was read.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.
1800906Status unverified
Enhanced torque converter and glow plug operation or brake switch DTC P0504
2005–2006grand-cherokee, liberty · NHTSA 10019630
Chrysler bulletin covering enhanced torque converter and glow plug operation, or brake switch DTC P0504.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.
Land RoverYour car
2005–2015 · LR3
Supported by vehicle dataLand Rover bulletin SSM52757 ties P0504 brake light switch DTCs to hard-to-release Park and warning lights on LR3, LR4 and Range Rover Sport. Only the NHTSA summary was read; whether the bulletin is still current is not verified.
SSM52757Status unverified
Excess brake pedal pressure to shift out of Park, brake light switch DTCs
2005–2015range-rover-sport, lr3, lr4 · NHTSA 10106041
Excess brake pedal pressure needed to shift the automatic out of Park, warning lights, and brake light switch DTCs (P0504-27, P0504-62, C1A96-64) or brakes showing drag; a related record is titled Brake Switch Adjustment and Setting Procedure.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.
FordYour car
2020–2022 · F-250 Super Duty
Supported by vehicle dataFord SSM 50848 lists P0504 with C0040 when F-Super Duty trucks will not shift out of Park. Only the NHTSA summary was read; whether the bulletin is still current is not verified.
SSM 50848Status unverified
Will not shift out of Park, DTC C0040 and/or P0504
2020–2022f-250-super-duty · NHTSA 10214488
F-Super Duty trucks may not shift out of Park with C0040 and/or P0504 present; the bulletin says to reference TSB 22-2044 to make sure no water is involved.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.
Related codes
No curated relationships for P0504 yet.
P0504 questions
Why is a brake switch code in the engine range?
The engine computer uses the brake switch signals, for example to cancel cruise control, and sets P0504 when the two disagree.
Sources and review
- P0504 Brake Switch A/B Correlation
- Generic OBDII P Codes P0500-P0599
- Chrysler flash 1803805: engine start and drivability at altitude / brake switch DTC P0504
- Jeep bulletin 1800906: Enhanced torque converter and glow plug operation or brake switch DTC P0504
- Land-Rover bulletin SSM52757: Excess brake pedal pressure to shift out of Park, brake light switch DTCs
- Ford bulletin SSM 50848: Will not shift out of Park, DTC C0040 and/or P0504
- Last reviewed
- Written by
- Saurabh K.
- Editorial review
- Pending
- Technician review
- Technician review pending
This page explains what a code usually means; it is not a substitute for a professional inspection. How we source and review · Report an error