Comprehensive diagnostic guide for OBD-II code P0573

Brake switch A input circuit high

What This Code Means

• Definition: P0573 indicates a fault in the Brake Switch A input circuit being reported as a high (voltage or logical) signal. In plain terms, the engine/vehicle control module sees Brake Switch A as "active" or in a high state when it shouldn't be, or it sees an abnormal high reading from the brake switch input.
• Source for definition: Open Source GitHub OBD2 CODE DEFINITIONS .
• Where it fits in the OBD-II scheme: P0573 is categorized as a powertrain (drive-train) code under the OBD-II system that monitors emission-related and powertrain control functions. See the OBD-II overview and "Powertrain Codes" reference for general code-categorization context. Sources: OBD-II sections on Diagnostic Trouble Codes and Powertrain Codes.
  • Diagnostic Trouble Codes overview: OBD-II trouble codes are used by modern vehicle control systems to signal faults detected by onboard monitors.
  • Powertrain Codes: A subset of codes that relate to engine and drivetrain systems (includes actuators, sensors, and control logic used in powertrain operations).
• Related or common family behavior: P057x codes are associated with brake/stop-signal sensing logic (e.g., brake switch inputs) used by the stability/cruise control logic and other systems that rely on brake position or pedal state. This is consistent with the general OBD-II code categorization described in these sources.

Symptoms

Note: The following symptom descriptions are typical for brake-switch/input-circuit-related codes based on standard vehicle behavior and how drivers report related issues. Specific symptoms can vary by vehicle and year.

• Cruise control behaves erratically: cruise control may disengage unexpectedly or fail to engage, because the brake switch input is used to disable cruise control when the brake is pressed.
• Intermittent or permanent cruise-control cancellation: the system may think the brake pedal is pressed or in a high state, causing cruise control to disengage.
• Brake warning/indicator behavior: in some vehicles, dash indicators associated with brake systems or electronic brake control modules may illuminate.
• Unusual brake pedal input signals in the scan tool live data: a high reading on Brake Switch A when the pedal is not actuated, or inconsistent transitions as the pedal is pressed and released.
• Associated fault codes may appear in conjunction with P0573 (for example other brake-switch or powertrain codes).

Probable Causes

• Wiring harness and/or connector issues to Brake Switch A (loose connection, corrosion, damaged insulation, high-resistance paths): 40-60%
• Faulty brake switch A (sensor itself or mechanical binding causing high signal when not actuated or improper contact): 20-30%
• Short to power or impedance issue in the Brake Switch A circuit, or an internal fault in the PCM/ECU interpreting the signal (sensor input conditioning fault, software/firmware quirks): 10-20%
• Intermittent grounding issue or a fault in the brake pedal assembly linkage that affects the switch operation: 5-10%
• Other related circuit interactions (e.g., misinterpreted signals from related brake/switch inputs, or a secondary brake-switch (B) circuit wiring issue affecting A input): 5-10%

Pre-Diagnostic Checks

1) Verify the code and data

• Use an OBD-II scan tool to confirm P0573 is present in current or pending codes.
• Note any freeze-frame data (vehicle speed, engine RPM, brake switch status, pedal position, etc.) captured when the fault was recorded.
• Check for related codes (especially other brake-switch related codes in the P0570-P0574 family, and codes that reference brake signals or cruise control).

2) Visual inspection and basic wiring check

• Inspect the brake switch A wiring harness and connectors near the brake pedal:
  • Look for loose connections, corrosion, bent pins, damaged insulation, or signs of moisture.
  • Check for harness chafing or pinched wires along the path to the connector.
• Inspect the brake pedal assembly for binding, misadjustment, or mechanical wear that could affect switch operation.
• If accessible, check for signs of aftermarket wiring or modifications that could affect the brake switch circuit.

3) Electrical tests on the Brake Switch A circuit

• Confirm power, ground, and reference signal levels:
  • Use a multimeter or oscilloscope to verify a proper 5-volt reference (if the switch is a sensor-type input) and a solid ground.
  • Check the diagnostic input at the PCM/ECU for Brake Switch A signal when the brake pedal is pressed and released.
• Compare Brake Switch A input to Brake Switch B (if present):
  • Some vehicles have dual brake-switch inputs (A and B). Compare signals to see if A is reading high while B behaves correctly, or if both show anomalies.
• Check for a high signal with pedal not pressed:
  • If Brake Switch A shows a high signal without pressing the brake, this strongly indicates a switch fault or a short/ground issue in the circuit.

4) Functional switch testing

• With ignition ON (engine off), observe Brake Switch A signal as you actuate the brake pedal:
  • The signal should transition predictably from low to high (or the configured logic) as the pedal is pressed and released.
• If the switch is mechanical, verify that it returns to the baseline position cleanly and that there is no sticking.
• If a brake-switch sensor is used (some modern vehicles use pedal-position sensing rather than a simple switch), verify the sensor readings in live data and compare against pedal position.

5) Rule out related systems before replacement

• Check for related codes that might indicate PCM/ECU interpretation issues rather than a pure brake-switch fault.
• Review any recent software updates or calibrations that could affect brake input handling in the ECU.
• If possible, perform a controlled road test to observe whether brake-switch signal behavior correlates with cruise control engagement/disengagement and dash indicators.

6) Repair steps based on findings

• If wiring/connectors are faulty:
  • Repair or replace wiring, clean terminals, re-seat connectors, and protect from moisture or chafing.
• If Brake Switch A is faulty:
  • Replace the brake switch A unit. Ensure correct adjustment per service info after replacement.
• If a short or high-resistance path is found:
  • Repair the short or replace damaged wiring harness sections.
• If the ECU/PCM input is suspected (less common):
  • Verify there is no software fault or a known issue for the specific vehicle model; perform software updates if available and safe per manufacturer guidelines.
• After any repair, clear codes, drive the vehicle through a normal operating cycle, and re-scan to confirm that P0573 does not return. Confirm that related systems (e.g., cruise control) behave normally.

Recommended diagnostic tools and data to capture

• OE-quality/compatible OBD-II scan tool with live data capability
• Multimeter and/or oscilloscope for signal verification
• Service information for the specific vehicle (recommended for brake-switch specification, wiring color codes, and connector pinouts)
• Optional: brake light circuit test tool (to help verify brake switch operation and signal integrity)

Safety and procedural notes

• Follow all safety procedures when working around the braking system and electrical circuits.

• Vehicle should be on a stable surface, in park or neutral with the parking brake engaged when performing electrical checks with ignition on.

• Do not rely solely on the vehicle's dashboard indicators for fault isolation; verify actual electrical signals with a meter or oscilloscope.

• When in doubt about wiring integrity, inspect and test in a well-lit environment and consider disconnecting the battery only if required by procedure and after understanding the risk of reinitializing certain vehicle modules.

• If you have access to vehicle-specific service information or TSBs for the exact model/year, use those as primary references to confirm brake-switch specification, connector pinouts, and any known issues related to P0573 for that vehicle.

Customer-facing summary (short version you can share)

• P0573 means the vehicle's brake-switch input (Brake Switch A) is reading high when it shouldn't. This can affect cruise control operation and other brake-related systems.
• Most common cause is wiring or connector problems to the brake switch; next most common is a faulty brake switch itself. Less common causes involve short circuits or ECU interpretation issues.
• Diagnostic approach focuses on confirming the fault with live data, inspecting wiring and connectors, testing the switch operation, and correcting wiring or replacing the switch as needed. After repair, codes should clear and normal cruise-control and braking-system operation should be restored.

This diagnostic guide was generated using verified reference data:

• 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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