Diagnostic Guide: P0572 - Brake Switch Input Circuit Fault Brake Pedal Switch

Important Notes

• What P0572 generally indicates: The open-source code definition available points to brake switch input circuits . Use this as a framework: P0572 is associated with the brake switch input circuit and its signals, and typically points to a fault in the brake switch circuit path (or its wiring/connector) rather than a pure ABS control module failure.
• How P0572 fits into the OBD-II system: OBD-II codes are diagnostic trouble codes generated by onboard controllers when monitored parameters detect out-of-range or fault conditions. Powertrain codes, including those tied to brake switch inputs and related circuits, are part of the broader DTC framework.
• Real-world symptom context: In a real complaint, P0572 appeared alongside braking/traction/ABS warnings (Traction Control Light, Service Trailer Braking System, ABS inoperative in slick conditions) and the Service Engine Light. This underscores that brake switch circuit faults can coincide with other braking system warnings and vehicle stability systems, and may show up intermittently or on startup.

What This Code Means

• Primary implication: A fault in the brake pedal switch input circuit (Brake switch input signal). This can involve the brake switch itself, its mounting/adjustment, or the wiring/connector in the circuit feeding the brake switch input to the vehicle's brake control module (and related systems such as ABS/traction control/cruise control) as reported by the open-source brake switch code definition.
• Vehicle behavior you might see with P0572 (based on symptom patterns): warning lights associated with braking and stability systems (ABS, Traction Control, Service Brake systems), potential intermittent service engine light activation, and possible changes in how the brake switch input is reported to controllers during startup or pedal application.

Symptoms

• Brake/ABS/Traction warnings: Traction Control Light, ABS/Brake warnings, service brake system messages may illuminate or fluctuate.
• Engine/ECU indicators: Service Engine Light may come on intermittently (as in the reported case), sometimes alongside P0572.
• Startup behavior: Warnings may appear on engine startup and can disappear or reappear later, depending on the circuit state (open/short, plug connection, etc.).
• Cross-coupled indicators: In some cases, other brake-related or stability-related warnings may be shown (e.g., trailer braking system notifications) if the vehicle's stability/anti-lock/brake circuits rely on the brake switch input to function correctly.

Probable Causes

Note: The NHTSA data provided contains a single reported case related to P0572 with braking/ABS/traction warnings. Using that limited data, here is a cautious probability guide. Real-world results will vary by vehicle make/model and year.

• Primary cause: Faulty brake switch input (brake pedal switch or its immediate circuitry)

• Secondary causes: Wiring harness or connector problems in the brake switch circuit (chafed wire, corroded terminals, poor grounds)

• Tertiary causes: Brake switch mounting/adjustment out of spec, or a failing brake switch that intermittently reports A/B circuit state

• Other possibilities (less likely based on the data but possible in practice): ABS/TCU/BCM software or sensor-related issues that misinterpret the brake switch input, or unrelated electrical faults causing cascading warning lights

Step-by-Step Diagnosis

Safety note: Brake systems are safety-critical. If you suspect an actual brake function problem (spongy brake pedal, soft pedal distance, or ABS/Traction system failure), treat test drives with caution. Use a controlled, low-speed environment when testing.

1) Gather and confirm

• Verify the code(s) present: P0572 (and any related P057x codes). Note any additional ABS, Traction, or Cruise Control codes that may provide context.
• Confirm symptoms: Are the brake lights functioning properly when applying the pedal? Are ABS/Traction/Service Brake warnings present at startup or during driving?

2) Visual inspection and basic checks

• Brake switch hardware: Inspect the brake light switch and bracket for physical damage, misalignment, or excessive play. Ensure the pedal returns completely to the off position and that the switch actuates with normal pedal travel.
• Mounting and routing: Look for bent brackets, loose fasteners, or stressed wiring near the brake pedal area.
• Wiring/connector inspection: Check for damaged insulation, chafed wires, pin corrosion, bent pins, or loose connectors in the brake switch circuit harness. Inspect grounds related to the brake switch circuit.
• Brake lights: With the ignition on and pedal pressed, verify brake lights illuminate consistently; verify that the brake switch changes state as the pedal is pressed and released.

3) Electrical/tests for brake switch circuits

• On-vehicle checks (typical expectations; adapt to your vehicle's wiring):
  • Measure continuity/ resistance of the brake switch input circuits A and B (as applicable on the vehicle). Confirm that the switch provides a signal change when the pedal moves from released to pressed.
  • Check for a clean 12V feed where the brake switch circuit is powered, and verify a solid ground path.
  • If the switch has two circuits (A and B), verify both circuits switch as the pedal is actuated. A failure in one circuit can trigger P0572-related interpretations by the powertrain or brake control modules.
• Live data perspective:
  • Using a scan tool, observe the brake switch input data or pedal position data if available. Confirm that the input state changes reliably with pedal movement and matches the actual pedal position (when pedal is pressed vs released).
  • Look for any concurrent DTCs from ABS/TCM/BCM that could illuminate when the brake switch input is faulty.

4) Wiring and connector checks

• Perform a thorough connector test: unplug, inspect, clean, reseat, and reconnect the brake switch connectors. Check for corrosion, bent pins, or damaged seals.
• Wiggle and re-seat tests: while monitoring live data, gently wiggle the wiring harness and connectors to identify intermittent faults.
• If you find a damaged wire or compromised connector, repair or replace the affected section or the entire switch wiring harness as needed.

5) Component-level assessment

• Brake switch replacement: If the switch shows physical wear, misalignment, or failure to change state consistently, replace the brake switch and re-test.
• Bracket alignment: Adjust or reinstall the brake switch to proper alignment per service specifications to ensure consistent pedal travel engagement.

6) Cross-check with related systems

• ABS/Traction / Trailer braking system/Brake control modules: If beyond the brake switch, scan for related codes in ABS/TCM/BCM that could indicate a cascading issue; verify proper operation of wheel speed sensors and brake modulators.
• If the brake switch circuit appears healthy, proceed to broader diagnostics for the ABS/TCU and cruise control input pathways, including harness routing, grounds, and software/ECU updates if applicable (within your shop's diagnostic protocol).

7) Re-test and verify

• Clear the DTCs (after repair) and perform a road test to confirm that P0572 does not return.
• Confirm that braking and stability systems (ABS/Traction) return to normal operation and that vehicle behavior matches expectations.
• Recheck brake lights and pedal switch operation to confirm durable repair.

Common Pitfalls

• Brake switch faults may cause cascading warnings that appear in ABS/Traction/Brake system messages, even if the root cause is simply the switch input signal. The NHTSA complaint illustrates how P0572 can appear alongside other braking-related warnings.
• Do not ignore a malfunctioning brake switch: a faulty brake switch can impact brake light operation and, in some vehicle configurations, influence the behavior of cruise control, ABS, or traction control logic.
• If you encounter intermittent faults: moisture, corrosion, or loose connectors are common culprits; re-seating connectors and cleaning corrosion can resolve intermittent P0572 signals.
• Documentation and cross-checks: Given the limited single-case data , document all findings and confirm with vehicle-specific service information for the exact make/model.

Summary

• P0572 is tied to brake switch input circuits, with the brake switch input signal (A/B) being the likely origin. The open-source brake switch definition supports the brake switch input circuit interpretation, and Wikipedia confirms that OBD-II POST/Powertrain codes monitor brake-related signals as part of the diagnostic framework. Real-world data shows P0572 can appear with ABS/Traction and other braking warnings, highlighting the interconnection of brake input signals with the vehicle's stability and brake systems.

• Diagnostic approach centers on validating the brake switch and its wiring, ensuring proper switch actuation and stable electrical signals, and then expanding to related modules if the fault persists.

• Use the above flow as a structured, safety-conscious, data-informed approach. If in doubt, escalate to vehicle-specific service information and consider consulting the OEM diagnostic procedure for P0572 on the exact make/model.

• NHTSA real-world symptom context: Traction Control Light, Service Trailer Braking System messages, ABS inoperative in slippery conditions, and P0572 codes appearing on engine startup in the provided complaint.

• Brake switch input concept mapping: Open Source GitHub entry titled (Brake switch A input low signal) as evidence that P0572-family codes relate to brake switch input circuits.

• OBD-II fundamentals: Wikipedia, OBD-II - Diagnostic Trouble Codes and OBD-II - Powertrain Codes, for general code structure, monitoring, and the scope of powertrain codes within emissions/diagnostic testing.

This diagnostic guide was generated using verified reference data:

• NHTSA Consumer Complaints: 1 real-world reports analyzed
• Wikipedia Technical Articles: OBD-II
• Open-Source OBD2 Data: N/A (MIT)

Content synthesized from these sources to provide accurate, real-world diagnostic guidance.

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