P0573 Cruise Control / Brake Switch "A" Circuit High

The P0573 diagnostic trouble code indicates that the engine or powertrain control module has detected an abnormally high electrical signal in the Cruise Control / Brake Switch “A” circuit.

This circuit is particularly important because the brake switch is one of the primary safety inputs used to control cruise control. When the driver presses the brake pedal, the control module must recognize the brake application and normally cancel or prevent cruise-control operation.

With P0573, the module is seeing a signal from the Brake Switch “A” circuit that is higher than the expected range.

This does not automatically mean that the brake switch itself has failed. The problem can also be in the wiring, connector, power supply, fuse, adjustment of the switch, or the input circuit inside the control module.

What Is the Brake Switch "A" Circuit?

The brake pedal switch is usually mounted near the brake pedal assembly.

Depending on the vehicle, the brake switch may contain multiple electrical circuits.

One circuit can operate the brake lamps, while another provides a signal to the ECU, TCM, ABS module, or cruise-control system.

This distinction is important because the brake lights can sometimes work normally even when the circuit monitored by the ECU has a fault.

The control module uses the brake-switch signal to determine whether the driver is braking.

When the brake pedal is released, the module expects one electrical state.

When the pedal is pressed, it expects another.

If the voltage on the relevant “A” circuit remains higher than the permitted value, P0573 may be stored.

Why Is the Brake Switch Important to Cruise Control?

Cruise control must be able to disengage immediately when the driver applies the brakes.

The brake switch therefore acts as a critical cruise-control cancellation input.

Under normal operation:

Brake pedal released → cruise-control system can remain active

Brake pedal pressed → cruise control receives a brake-applied signal and disengages

If the ECU cannot trust the brake-switch signal, it may disable cruise control completely.

This is why a relatively small electrical problem in the brake-switch circuit can result in the cruise-control system becoming unavailable.

What Does “Circuit High” Mean?

“High” means that the control module is detecting a voltage or electrical state above the expected range for that circuit.

It does not necessarily mean that the brake pedal is physically stuck.

For example, the circuit may be receiving excessive voltage because of:

• A short to battery voltage

• Incorrect wiring

• A damaged switch

• A failed connector

• An incorrect power supply

• An internal circuit problem

An open circuit can also produce a high reading on some vehicle designs if the ECU input contains an internal pull-up resistor.

Therefore, P0573 should not be interpreted simply as “the brake switch has too much voltage.”

The actual circuit design must be considered.

Common Causes of P0573

Faulty brake pedal switch

The internal contacts may fail and leave the circuit in the wrong electrical state.

Brake switch incorrectly adjusted

On some vehicles, the switch position relative to the brake pedal is critical. If it is incorrectly adjusted, the switch may change state at the wrong time.

Short to battery voltage

The signal wire may be contacting a powered circuit, causing the ECU to see a higher voltage than expected.

Damaged wiring

A wire can become damaged, stretched, pinched, or chafed near the pedal assembly.

Corroded connector

Moisture or corrosion can alter the electrical characteristics of the circuit.

Loose or damaged terminals

A terminal that does not make proper contact can cause an incorrect or unstable signal.

Incorrect replacement brake switch

A replacement switch that looks physically identical may have different internal contacts or circuit logic from the original specification.

Fuse or power-supply problem

Some brake-switch circuits receive their power through a dedicated fuse. An abnormal supply can affect the monitored signal.

ECU input problem

An internal fault in the module's input circuit is possible, although this should be considered only after the external circuit has been verified.

Symptoms of P0573

The symptoms can vary depending on the vehicle.

Possible symptoms include:

• Cruise control does not operate

• Cruise control cannot be activated

• Cruise control disengages unexpectedly

• Check Engine Light

• Cruise-control warning light

• Brake lights behave incorrectly

• Brake lights remain illuminated

• Brake lights do not illuminate

• Cruise control becomes intermittent

• Other systems report an implausible brake-switch signal

One particularly important point is that P0573 can exist even when the brake lights appear to work normally.

The reason is that the vehicle may use multiple contacts or circuits inside the brake switch.

Can the Brake Lights Still Work with P0573?

Yes.

This is one of the most important things to understand when diagnosing the code.

A brake pedal switch may contain more than one electrical circuit.

For example, one contact may control the brake lamps while another supplies the signal used by the ECU.

If the ECU-monitored contact fails, the brake lamps may still function.

Therefore:

“The brake lights work, so the brake switch is good” is not a reliable conclusion.

The relevant circuit must be tested directly.

How to Diagnose P0573

Start by checking whether there are any other stored codes.

Codes from the ABS, transmission, engine, or body-control systems can be useful because several modules may monitor the brake-switch signal.

Then observe the brake-switch status using a scan tool if live data is available.

With the brake pedal released, the ECU should normally report one state.

When the brake pedal is pressed, the state should change.

If the scan tool continues to show the brake as pressed when the pedal is released, or shows an implausible state, the circuit needs further testing.

Check the Brake Switch Mechanically

Before reaching for a multimeter, inspect the physical installation.

Check:

• Brake pedal movement

• Switch mounting

• Switch adjustment

• Switch plunger position

• Pedal return

• Physical damage around the pedal assembly

A brake switch that is incorrectly positioned can produce electrical symptoms that look like a failed switch.

On some vehicles, the switch is self-adjusting during installation, so installation procedure is important.

Test the Brake Switch

The switch should be tested according to the manufacturer's wiring diagram.

Depending on its design, you may need to check:

• Supply voltage

• Signal voltage

• Continuity

• Contact state with pedal released

• Contact state with pedal pressed

A switch may have multiple terminals, so simply checking whether two pins have continuity is not sufficient.

The technician needs to identify which terminals belong to the “A” circuit.

The electrical state should then be compared with the manufacturer's specifications.

Check for a Short to Power

Because P0573 is a high circuit code, a short to battery or another powered circuit is an important possibility.

With the circuit isolated as required by the manufacturer's procedure, check whether the signal wire is receiving voltage when it should not.

If a signal wire has battery voltage continuously, inspect the harness for contact with:

• Battery-positive wiring

• Ignition power

• Other powered circuits

• Damaged insulation

• Incorrect aftermarket wiring

An aftermarket electrical accessory installed near the pedal or fuse box can occasionally introduce unexpected connections.

Check for an Open Circuit

An open circuit should not be overlooked.

Depending on the input design, a broken wire or disconnected switch can cause the ECU input to rise toward its internal pull-up voltage.

Check continuity between the appropriate switch terminal and the control-module terminal.

Also check for excessive resistance.

A wire can have continuity but still have enough resistance to cause an abnormal signal under operating conditions.

Inspect the Connector

The brake-switch connector is located in an area where it can be exposed to movement, vibration, and contamination.

Inspect for:

• Corrosion

• Loose pins

• Bent terminals

• Water contamination

• Damaged locking tabs

• Terminals pushed backward inside the connector

A poor terminal connection can cause a high or unstable signal without any visible damage to the wire itself.

Look at Live Data Before Replacing Parts

Live data is particularly valuable for P0573.

If the scan tool shows:

Brake pedal released → Brake OFF

Brake pedal pressed → Brake ON

and the status changes consistently, the basic switch signal may be functioning correctly at that moment.

If it shows:

Brake pedal released → Brake ON

then the ECU is receiving an incorrect brake signal and the circuit should be investigated.

If the status changes randomly, an intermittent switch, connector, or wiring fault becomes more likely.

P0573 vs. P0572

These codes concern the same general brake/cruise-control input but describe different electrical conditions.

P0572 – Cruise Control / Brake Switch “A” Circuit Low

The control module detects a signal below the expected range.

P0573 – Cruise Control / Brake Switch “A” Circuit High

The control module detects a signal above the expected range.

The distinction helps determine the direction of electrical testing.

With P0572, the investigation tends to focus on why the circuit is being pulled low.

With P0573, the investigation should consider excess voltage, a short to power, an open circuit, or an incorrect switch state, depending on the circuit design.

P0573 vs. P0575

P0575 concerns the Cruise Control Input Circuit itself.

P0573 specifically identifies the Cruise Control / Brake Switch “A” circuit.

This distinction is important because P0573 points the diagnostic process toward the brake-switch input and its associated wiring rather than the multifunction cruise-control buttons.

Can a Bad Brake Switch Cause P0573?

Yes.

A defective brake switch is one of the first components worth testing.

But it should not automatically be replaced.

If the switch produces the correct output but the ECU sees a high signal, the problem is further along the circuit.

Conversely, if the ECU receives a high signal directly from the switch and the switch does not change state correctly when the pedal is operated, the switch becomes the stronger suspect.

Can a Wiring Problem Cause P0573?

Yes, and it is an important possibility.

A wire shorted to a power source can create a high input.

An open circuit can also potentially result in a high input when the ECU uses a pull-up circuit.

This is why simply replacing the brake switch can fail to solve P0573 when the real problem is in the harness or connector.

Is P0573 Serious?

P0573 generally does not indicate an engine-internal problem, but it should not be ignored.

The brake-switch circuit is directly related to cruise-control safety logic.

If the ECU cannot determine reliably whether the brake pedal is being pressed, it may disable cruise control.

More importantly, if the brake lamps themselves are affected, the problem becomes a direct road-safety issue.

Before driving normally, verify that the brake lights operate correctly every time the pedal is pressed.

What Is the Correct Repair?

The correct repair depends on the test results.

Possible repairs include:

• Replacing the brake pedal switch

• Correctly adjusting the switch

• Repairing a shorted wire

• Repairing an open circuit

• Replacing a damaged connector terminal

• Repairing the brake-switch power supply

• Correcting an incorrect fuse or wiring issue

• Repairing a control-module input circuit

• Correcting an installation error from a previous repair

The important point is that P0573 identifies an electrical condition, not a guaranteed failed component.

Final Diagnostic Summary

P0573 means the control module has detected a high electrical signal in the Cruise Control / Brake Switch “A” circuit.

The brake switch is an important suspect, but the diagnosis should also include the switch adjustment, wiring, connector terminals, power supply, and ECU input.

A useful diagnostic sequence is:

Check brake-light operation → scan live brake-switch data → identify the “A” circuit → measure its voltage/state → test the brake switch → inspect wiring and connectors → check for short to power or an open circuit → verify the ECU input.

If the brake switch produces the wrong signal, replace or correctly adjust the switch. If the switch is working correctly but the ECU still sees a high signal, follow the circuit toward the control module.

The key point is that P0573 is a brake-switch input circuit problem, not simply a “bad cruise control” code.