P0572 Cruise Control / Brake Switch "A" Circuit Low

When P0572 is stored, the control module has detected a lower-than-expected electrical signal in the Brake Switch "A" circuit.

This circuit is particularly important because the brake switch is one of the main safety inputs used by the cruise control system. When the driver presses the brake pedal, the system needs to know immediately so it can cancel cruise control and stop applying automatic throttle control.

For this reason, a problem with the brake-switch signal can cause the cruise control system to be disabled even when the engine, throttle, and transmission are operating normally.

The word “Low” in P0572 refers to the electrical signal in the circuit. It does not mean that the brake pedal is physically low or that the braking pressure is insufficient.

Why Does Cruise Control Need the Brake Switch?

Cruise control cannot operate safely without knowing when the driver is pressing the brake pedal.

Imagine that the vehicle is maintaining 100 km/h with cruise control active. The driver presses the brake because traffic ahead is slowing down.

The cruise control system must immediately recognize the brake-pedal input and cancel the automatic speed control.

The brake switch therefore acts as an important safety signal.

Depending on the vehicle, there may be more than one brake-switch circuit. One circuit may be used for the brake lamps while another is monitored by the ECM, PCM, BCM, ABS module, or cruise-control system.

This is why the brake lights can sometimes appear to work normally even though a brake-switch-related diagnostic code is present.

What Does “Circuit Low” Mean?

P0572 does not simply mean that the brake switch is turned off.

It means the control module is seeing an electrical condition that is below the expected threshold for the Brake Switch "A" circuit.

This can happen if the circuit is being pulled toward ground, if the expected voltage is missing, or if there is excessive resistance or another electrical problem in the circuit.

A common example would be a damaged wire contacting ground.

Another possibility is a defective brake switch that cannot produce the correct electrical state when the pedal is released or pressed.

The exact voltage expected by the module depends on the vehicle's electrical design.

The Brake Switch Does More Than Turn on the Brake Lights

On many vehicles, the brake switch has more than one electrical function.

One portion of the switch may control the brake lamps, while another signal is sent to the vehicle's control modules.

This creates an important diagnostic situation:

The brake lights can work, but P0572 can still be present.

If the part contains multiple internal contacts, one circuit can fail while another continues working.

Therefore, checking only whether the brake lamps illuminate is not enough to rule out the brake switch.

What Can Cause P0572?

A defective brake switch is an obvious possibility, but it is not the only one.

Possible causes include:

• Faulty brake pedal switch

• Short to ground in the Brake Switch "A" circuit

• Damaged wiring

• Corroded connector terminals

• Loose electrical connection

• Incorrect switch adjustment

• Brake switch installed incorrectly

• Excessive resistance in the circuit

• Missing or incorrect power supply

• Poor ground

• Damaged connector

• Fuse or power-distribution problem

• Wiring problem between the brake switch and control module

• Fault in another module communicating brake-switch status

• Rarely, a PCM/ECM or BCM fault

The mechanical adjustment of the brake switch is also important on some vehicles.

If the switch is positioned incorrectly, it may not change states at the correct point when the brake pedal is pressed and released.

What Symptoms Can P0572 Cause?

The most common symptom is cruise control that will not operate.

The control module may deliberately disable cruise control because it cannot reliably determine whether the brake pedal is being pressed.

Other symptoms can include:

• Cruise control cannot be activated

• Cruise control disengages unexpectedly

• Brake lights remain on

• Brake lights fail to illuminate

• Brake lights work intermittently

• Check Engine Light comes on

• Cruise control warning appears

• ABS or stability-control warnings may appear in some vehicles

• Other brake-switch-related codes may be stored

The exact symptoms depend on which part of the brake-switch circuit has failed.

The Brake Lights Give You an Important Clue

One of the first things to check is what the brake lamps are doing.

If the brake lights are always on, the brake switch may be stuck in the activated position, incorrectly adjusted, or its wiring may have a problem.

If the brake lights never illuminate, the problem may involve the switch, its power supply, fuse, wiring, or lamp circuit.

If the brake lights operate normally but P0572 remains stored, the control-module side of the brake-switch circuit deserves closer attention.

Again, the exact switch configuration varies by vehicle.

How Should P0572 Be Diagnosed?

The first step is to scan the vehicle for all stored and pending codes.

This is especially important because brake-switch information can be shared with several systems.

If you also have ABS, ESC, transmission, or communication-related codes, they may help explain why the brake-switch signal is considered abnormal.

After scanning, check the brake lights and physically observe the brake pedal switch.

The switch should change state at the correct point as the pedal is pressed and released.

A switch that is loose, incorrectly positioned, damaged, or contaminated may not operate correctly.

Use Live Data if Available

A diagnostic scanner can make P0572 much easier to diagnose if the vehicle provides brake-switch status in live data.

The control module may display something such as:

Brake Switch: OFF

and then:

Brake Switch: ON

as the brake pedal is operated.

Press and release the pedal several times while watching the data.

If the physical pedal is released but the module continues to report that the brake is applied, there is a problem that needs further investigation.

Likewise, if the brake is pressed but the module never recognizes the change, the switch circuit may not be producing the expected signal.

This test can quickly tell you whether the module is actually receiving the brake-switch information.

Check the Switch Adjustment

On some vehicles, the brake switch position is critical.

The switch must be positioned so that the pedal movement causes the internal contacts to change state at the correct point.

If the switch has been replaced recently, moved during repair, or installed incorrectly, adjustment should be checked.

A switch can be electrically functional but still produce the wrong signal at the wrong time because it is physically positioned incorrectly.

This is an important distinction between an electrical failure and an adjustment problem.

Check the Wiring for a Short to Ground

Because P0572 indicates a low electrical condition, a short to ground is one of the faults worth investigating.

Inspect the wiring between the brake switch and the relevant control module.

Look for:

• Damaged insulation

• Pinched wiring

• Chafing

• Corrosion

• Water contamination

• Loose terminals

• Previous repairs

• Wires contacting metal brackets

A damaged wire can occasionally touch ground only when the brake pedal or wiring harness moves.

That can make the fault intermittent and difficult to reproduce.

Don't Assume the Brake Switch Is Bad

Replacing the brake switch is relatively easy on many vehicles, which makes it tempting to replace it immediately.

But P0572 does not specifically say:

“Brake switch defective.”

It says that the control module has detected a low electrical condition in the Brake Switch "A" circuit.

The switch, wiring, connector, power supply, or control-module input can all produce that condition.

If a new switch is installed without checking the circuit and the code remains, the real problem may never have been the switch.

Why a Brake-Switch Problem Can Affect More Than Cruise Control

The brake-switch signal is often used by multiple vehicle systems.

Depending on the vehicle, brake-pedal information may be shared with:

• Cruise control

• ECM/PCM

• ABS/ESC

• Transmission control

• Brake-light control

• Body-control systems

Therefore, a single brake-switch circuit problem can sometimes produce several seemingly unrelated symptoms.

For example, cruise control may stop working while an ABS or transmission-related code is also stored.

In that situation, it is important to look for a common brake-switch signal problem rather than treating every code as a separate failure.

Can You Drive With P0572?

The answer depends on how the brake-switch circuit is behaving.

If the only symptom is that cruise control has been disabled, the vehicle may otherwise drive normally.

However, if the brake lights are not functioning correctly, the situation becomes much more serious.

Brake lights are an essential safety system. A vehicle should not be driven normally if the brake lamps fail to illuminate when the brake pedal is pressed.

Likewise, if multiple ABS, ESC, or braking-system warnings are present, the vehicle should be inspected before continued driving.

P0572 vs. P0571 and P0573

These three codes are closely related:

P0571 – Cruise Control / Brake Switch "A" Circuit

P0572 – Cruise Control / Brake Switch "A" Circuit Low

P0573 – Cruise Control / Brake Switch "A" Circuit High

P0571 is a more general circuit malfunction.

P0572 specifically indicates that the control module sees a low electrical signal.

P0573 indicates a high electrical signal.

This distinction can help narrow the diagnosis, particularly when combined with live-data readings and an inspection of the brake-switch circuit.

The Most Useful Way to Think About P0572

P0572 is essentially telling you that the vehicle's control module does not trust the electrical signal it is receiving from the Brake Switch "A" circuit.

Because the brake switch is a safety-critical input for cruise control, the system may simply disable cruise control until the problem is corrected.

The diagnosis should begin with the brake lights and switch operation, followed by switch adjustment, live-data status, wiring, connectors, power supply, and the actual electrical signal reaching the control module.

If the brake switch works correctly but the module still sees a low signal, the wiring and circuit itself become much more important.

The goal is not simply to replace the brake switch. The goal is to determine why the control module is seeing a low Brake Switch "A" signal and correct that specific fault.