Code
P0504
Generic
P — Powertrain
Brake Switch A/B Correlation
Views:
UK: 35
EN: 91
RU: 57
AI status
Completed
Completed
100%
Causes
- Faulty brake light / brake pedal position switch (one or both switches)
- Misadjusted or sticking brake switch (mechanical alignment)
- Damaged wiring or poor connector connection between switches and control module
- Short to voltage or ground on one circuit causing inconsistent readings
- Corroded grounds or poor chassis ground
- Aftermarket electrical modifications (alarms, trailer wiring) affecting circuits
Symptoms
- Malfunction Indicator Lamp (MIL) or ABS/Traction lights illuminated depending on network logic
- Cruise control disabled or will not set/resume
- Brake lights may be inoperative, stuck on, or intermittent
- Shift interlock may not release (vehicle won’t shift out of Park) on some models
- Reduced or disabled adaptive braking/driver assist functions
- Possible no-start inhibit on some vehicles if brake input logic used for start/stop
What to check
- Retrieve freeze frame and live data with a scan tool; monitor both Brake Switch A and B states while operating the pedal
- Visual inspection of brake switch(s), mounting, and pedal linkage for damage or misadjustment
- Inspect connectors for corrosion, bent pins, water intrusion and secure fit
- Check for Diagnostic Trouble Codes in related modules (ABS, BCM) and for communication errors
- Measure supply voltage and ground at switch connectors with key on, engine off
- Continuity/resistance check of switch circuits and between switches and control module
Signal parameters
- Brake Switch A/B states: expected to change together (e.g., both 0/1 or OFF/ON) within the same pedal travel
- Typical logic voltage: LOW ≈ 0–0.5 V, HIGH ≈ 4.5–12 V depending on vehicle design (confirm with service manual)
- Ignition-switched 12 V supply present at switch when required
- Continuity: near 0 ohms when closed, open/infinite when open (verify per circuit design)
- Scan tool values: switch status bits or percent indicators should match physical pedal position
Diagnostic algorithm
- Connect a OBD-II scan tool and record freeze frame and live data for both Brake Switch A and B while cycling the brake pedal slowly and rapidly. Note any mismatches, delays or chatter.
- Visually inspect switch mounting, plunger travel and pedal stop. Confirm both switches are actuated by the pedal at the same travel point.
- With ignition ON, measure reference voltage and ground at each switch connector. Compare to vehicle spec. Check for voltage drop during operation.
- Operate the brake pedal while probing signal wire and observe voltage transitions. Verify both circuits change state together. If one circuit is incorrect, isolate that circuit.
- If a wire fault is suspected, disconnect switch and perform continuity/resistance checks back to the control module connector. Repair/replace damaged wires or connectors.
- If switches and wiring check good, swap or bench-test the switch(es) (if removable) or replace the suspect switch and re-test.
Likely causes
- Single faulty or intermittent brake switch
- Switch plunger out of adjustment so A and B signals change at different pedal positions
- Wiring harness damage at the pedal area or connector corrosion
- Intermittent ground or power feed to one switch
- Connector pushed out or pin damage at switch or module
Fault status
Status
Brake Switch A/B Correlation — PCM detected inconsistent or non-correlating signals between dual brake switch inputs indicating a possible switch, wiring, or module fault.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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Code
P0504
LAND ROVER
P — Powertrain
Brake Switch Correlation A / B
Views:
UK: 21
EN: 63
RU: 40
AI status
Completed
Completed
100%
Causes
- Faulty brake light / brake pedal position switch (one or both switches)
- Misadjusted or sticking brake switch (mechanical alignment)
- Damaged wiring or poor connector connection between switches and control module
- Short to voltage or ground on one circuit causing inconsistent readings
- Corroded grounds or poor chassis ground
- Aftermarket electrical modifications (alarms, trailer wiring) affecting circuits
Symptoms
- Malfunction Indicator Lamp (MIL) or ABS/Traction lights illuminated depending on network logic
- Cruise control disabled or will not set/resume
- Brake lights may be inoperative, stuck on, or intermittent
- Shift interlock may not release (vehicle won’t shift out of Park) on some models
- Reduced or disabled adaptive braking/driver assist functions
- Possible no-start inhibit on some vehicles if brake input logic used for start/stop
What to check
- Retrieve freeze frame and live data with a scan tool; monitor both Brake Switch A and B states while operating the pedal
- Visual inspection of brake switch(s), mounting, and pedal linkage for damage or misadjustment
- Inspect connectors for corrosion, bent pins, water intrusion and secure fit
- Check for Diagnostic Trouble Codes in related modules (ABS, BCM) and for communication errors
- Measure supply voltage and ground at switch connectors with key on, engine off
- Continuity/resistance check of switch circuits and between switches and control module
Signal parameters
- Brake Switch A/B states: expected to change together (e.g., both 0/1 or OFF/ON) within the same pedal travel
- Typical logic voltage: LOW ≈ 0–0.5 V, HIGH ≈ 4.5–12 V depending on vehicle design (confirm with service manual)
- Ignition-switched 12 V supply present at switch when required
- Continuity: near 0 ohms when closed, open/infinite when open (verify per circuit design)
- Scan tool values: switch status bits or percent indicators should match physical pedal position
Diagnostic algorithm
- Connect a OBD-II scan tool and record freeze frame and live data for both Brake Switch A and B while cycling the brake pedal slowly and rapidly. Note any mismatches, delays or chatter.
- Visually inspect switch mounting, plunger travel and pedal stop. Confirm both switches are actuated by the pedal at the same travel point.
- With ignition ON, measure reference voltage and ground at each switch connector. Compare to vehicle spec. Check for voltage drop during operation.
- Operate the brake pedal while probing signal wire and observe voltage transitions. Verify both circuits change state together. If one circuit is incorrect, isolate that circuit.
- If a wire fault is suspected, disconnect switch and perform continuity/resistance checks back to the control module connector. Repair/replace damaged wires or connectors.
- If switches and wiring check good, swap or bench-test the switch(es) (if removable) or replace the suspect switch and re-test.
Likely causes
- Single faulty or intermittent brake switch
- Switch plunger out of adjustment so A and B signals change at different pedal positions
- Wiring harness damage at the pedal area or connector corrosion
- Intermittent ground or power feed to one switch
- Connector pushed out or pin damage at switch or module
Fault status
Status
Brake Switch A/B Correlation — PCM detected inconsistent or non-correlating signals between dual brake switch inputs indicating a possible switch, wiring, or module fault.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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