Brake Switch "A" Circuit High
Diagnostic trouble code P0573 indicates that the engine control module has detected an unexpectedly high electrical voltage signal from the brake switch 'A' circuit. This typically means the circuit is shorted to power or the brake pedal position switch has failed internally.
While the vehicle can usually still be driven, malfunctioning brake lights pose a significant safety hazard to other drivers. Additionally, this code may prevent the vehicle from shifting out of park or starting in push-to-start models.
Common symptoms
- Illuminated Check Engine Light
- Cruise control system is completely inoperative
- Brake lights remain on continuously or fail to illuminate
- Inability to shift the transmission out of Park
- Vehicle may not start (especially in push-to-start systems)
Likely causes
- Faulty or worn brake light switch
- Misadjusted brake light switch or missing pedal stopper pad
- Short to power in the brake switch wiring harness
- Corroded, loose, or damaged electrical connector at the switch
- Blown fuse related to the brake light circuit
- Faulty Powertrain Control Module (PCM) or Body Control Module (BCM) (rare)
What to check before replacing parts
Visually inspect the brake light switch and its physical adjustment at the brake pedal.
Look for: Ensure the switch is securely mounted, the plunger moves freely when the pedal is pressed, and the physical stopper pad on the pedal is intact.
Observe the operation of the vehicle's brake lights.
Look for: If the brake lights stay on without pressing the pedal, or fail to turn on when pressed, it confirms a switch or circuit failure.
Test the brake switch for proper continuity using a digital multimeter.
Look for: The switch should show continuity when closed and no continuity when open, according to the manufacturer's specifications. A lack of change indicates an internally failed switch.
Check the brake switch connector and wiring for proper voltage and ground.
Look for: Verify that the reference voltage is present and that the signal wire is not shorted to a constant 12V power source when the switch is disconnected.
Inspect the wiring harness leading from the brake switch to the PCM/BCM.
Look for: Look for chafed wires, melted insulation, or pinched harnesses that could cause a short to voltage in the 'A' circuit.
This page explains the generic P0573 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
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