A faulty brake pedal position switch that is stuck closed or has internal contact failure, sending a constant high voltage signal.; A short to battery voltage in the signal wire between the brake switch and the PCM, often caused by chafed insulation against a metal bracket.; Corroded or loose electrical connectors at the brake switch or PCM, creating high resistance that the PCM interprets as a high signal.; A misadjusted brake switch that remains engaged even when the pedal is released, common after pedal or switch replacement.; A defective PCM driver circuit, though this is rare and should only be suspected after all other possibilities are ruled out.; Aftermarket accessories such as trailer brake controllers or remote starters improperly tapped into the brake signal wire.

DTC codes / P05xx · Vehicle speed, idle control and auxiliary inputs / P0573

P0573Brake Switch 'A' Circuit High

Q: What does code P0573 mean?

Brake Switch 'A' Circuit High. P0573 indicates the powertrain control module (PCM) has detected an abnormally high voltage on the brake switch 'A' circuit, which is the primary input used to determine when the brake pedal is pressed. The PCM expects this signal to switch between low and high voltage as the pedal moves, and a continuous high reading tells the module the brakes are either stuck on or the circuit is shorted to power.

P0573 indicates the powertrain control module (PCM) has detected an abnormally high voltage on the brake switch 'A' circuit, which is the primary input used to determine when the brake pedal is pressed. The PCM expects this signal to switch between low and high voltage as the pedal moves, and a continuous high reading tells the module the brakes are either stuck on or the circuit is shorted to power.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaVehicle speed, idle control and auxiliary inputs

Symptoms you may notice

The brake lights may stay illuminated constantly, even with the pedal released.
The cruise control may fail to engage or disengage unexpectedly because the PCM cannot trust the brake status.
The transmission may shift harshly or refuse to go into overdrive, as the PCM alters shift strategy when it believes the brakes are applied.
A stored P0573 code with the malfunction indicator lamp (MIL) illuminated on the dashboard.
Often no symptoms besides the warning light, especially if the fault is intermittent or only affects the signal to the PCM.
On some vehicles, the engine may idle poorly or stall when coming to a stop due to incorrect torque converter clutch scheduling.

Common causes, most likely first

A faulty brake pedal position switch that is stuck closed or has internal contact failure, sending a constant high voltage signal.
A short to battery voltage in the signal wire between the brake switch and the PCM, often caused by chafed insulation against a metal bracket.
Corroded or loose electrical connectors at the brake switch or PCM, creating high resistance that the PCM interprets as a high signal.
A misadjusted brake switch that remains engaged even when the pedal is released, common after pedal or switch replacement.
A defective PCM driver circuit, though this is rare and should only be suspected after all other possibilities are ruled out.
Aftermarket accessories such as trailer brake controllers or remote starters improperly tapped into the brake signal wire.

How to diagnose and fix it

Verify the brake lights operate correctly with the pedal released and pressed; if they stay on, inspect the switch and its adjustment first.
Use a digital multimeter to measure voltage on the signal wire at the brake switch connector with the pedal released and pressed, comparing to the manufacturer's specification.
Disconnect the brake switch and check for battery voltage on the signal wire with the switch removed; if voltage remains, trace the wire for a short to power.
Inspect the brake switch connector and PCM connector for corrosion, pushed pins, or loose terminals, and repair as needed.
Check for aftermarket wiring taps on the brake circuit and remove or repair any improper connections.
If the switch and wiring test good, substitute a known-good brake switch and clear the code to see if it returns.
As a last resort, follow the manufacturer's diagnostic flow for PCM testing, including checking for a faulty internal driver before replacing the PCM.

Brake switch faults that fool good technicians

A brake switch that tests fine with a multimeter can still set P0573 intermittently due to internal arcing or a worn plunger that only misbehaves at certain temperatures.
The PCM may set P0573 even when the brake lights work perfectly, because the switch often contains two separate internal contacts: one for the lights and one for the PCM signal.
A short to power in the brake signal wire can be caused by a failed cruise control servo or trailer wiring harness, so always check those circuits before condemning the switch.
On many vehicles, the brake switch is also used by the electronic stability control (ESC) system, and a faulty switch can set wheel speed or yaw rate codes alongside P0573.
Replacing the brake switch without checking the pedal free play and switch adjustment often leads to a repeat failure, as the new switch can be preloaded and fail prematurely.

Can I keep driving with P0573?

You can usually drive the vehicle to a repair shop, but avoid relying on cruise control and be aware that the transmission may shift abnormally. If the brake lights are stuck on, other drivers may not know when you are braking, so have it checked promptly.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.