P0504

Code

LAND ROVER P — Powertrain

Brake Switch Correlation A / B

Brand: LAND ROVER

Type: P — Powertrain

Views: UK: 31 EN: 100 RU: 57

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Page language: EN

Causes

Faulty or worn brake light / brake pedal position switch (single or dual-output type)
Brake switch out of adjustment or mechanically binding (incorrect pedal travel)
Damaged wiring harness, chafed insulation, short to ground or to battery
Corroded or loose connector terminals at switch or control module
Poor ground or low battery/voltage anomalies
Aftermarket parts or incorrect replacement switch

Symptoms

Brake lights stuck ON or OFF
Cruise control disabled or unavailable
ABS, traction control or other related warning lamps illuminated
Shift interlock or ignition interlock faults (unable to shift out of Park or start inhibit)
Possible unexpected vehicle behavior tied to brake input

What to check

Read and record all stored codes and freeze-frame data; check for related codes (ABS, BCM)
Attempt to recreate the fault and observe whether it is permanent or intermittent
Visually inspect brake switch, pedal linkage and connectors for damage, contamination, or misadjustment
Operate the brake pedal while observing brake lights and live data for Brake Switch A/B signals
Perform a wiggle test on the harness and connectors while monitoring live data
Check battery voltage and grounds before performing signal tests

Signal parameters

Brake switch circuits are typically discrete on/off signals referenced to vehicle 12 V or vehicle ground (some modules use 0–5 V logic).
Expected states: one channel may be normally-open and the other normally-closed, or both should change state simultaneously when pedal is pressed.
When released: one or both channels should be at their defined idle voltage (0 V or pull-up voltage). When pressed: channels should switch to the complementary defined voltage (battery voltage or 5 V logic).
Transient spikes or oscillation on either circuit indicate intermittent connection or short

Diagnostic algorithm

Connect a scan tool and confirm P0504 is present; note freeze frame and related codes. Clear codes and attempt to re-trigger to observe conditions.
Visually inspect the brake pedal, switch mounting and connectors. Verify switch actuator engages fully and pedal free play is within spec.
With ignition on, monitor live data: observe Brake Switch A and B states while operating pedal. Confirm both change state and correlate to brake lights.
Measure voltage/continuity at the switch terminals with a multimeter while operating the pedal. Compare measured voltages to expected logic (0/5V or 0/12V depending on vehicle).
If one circuit doesn't change or shows intermittent behavior, inspect/repair wiring from the switch to the BCM/PCM: check for shorts, opens, chafing, and corrosion. Perform back-probing at connector and module if needed.
Repair or replace the brake switch if switch outputs are incorrect or inconsistent. Use OEM or compatible part and set correct switch adjustment.
After repairs, clear DTCs, perform a functional test (operate pedal, verify brake lights, cruise/shift interlock behavior) and road test to confirm fault does not return.
If wiring and switch test good but code persists, suspect BCM/PCM input fault or software issue — consult service information for module testing, reprogramming or replacement.

Likely causes

Failed or misadjusted brake switch
Open, short, or intermittent wiring between switch and control module
Corroded/loose connector at switch
Module input fault (less common)

Fault status

⚠️ Status

Brake Switch A/B correlation fault — the two brake switch inputs do not agree. May affect brake lights, cruise control, ABS/traction or shift interlock.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours

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Repair manuals

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P0504 — Brake Switch Correlation A / B