P0572

What Does Code P0572 Mean?

DTC P0572, which translates to “Cruise Control/Brake Switch A Circuit Low,” indicates that the Powertrain Control Module (PCM), or in some cases the Engine Control Module (ECM) in conjunction with other modules, has detected an anomalous voltage condition on the dedicated ‘A’ circuit of the Brake Pedal Position Sensor/Switch (BPPS). The ‘A’ circuit typically refers to the primary input signal that the PCM utilizes for critical functions such as cruise control disengagement, torque converter clutch (TCC) control, and often integration with anti-lock braking (ABS) and electronic stability control (ESC) systems. A “Circuit Low” condition signifies that the PCM is receiving a voltage signal on this circuit that is continuously below the manufacturer’s specified operational threshold, often near zero volts or indicating a constant ground, when the circuit should either be open (high impedance) or registering a higher voltage. This implies that the circuit is either shorted to ground somewhere in the wiring harness, or the brake switch itself is internally shorted or stuck in a closed (activated) position, thereby erroneously signaling that the brake pedal is depressed even when it is not. The PCM registers this discrepancy after monitoring the low voltage state for a calibrated duration, identifying a fault that directly impacts safety-critical systems and powertrain management.

Common Symptoms

• Cruise control system becomes inoperative or fails to engage.
• Malfunction Indicator Lamp (MIL) illumination on the dashboard.
• Difficulty shifting the transmission out of Park, particularly in vehicles with shift interlock systems that rely on brake pedal input.
• Intermittent or complete failure of brake lights (less common for ‘A’ circuit, but possible if the switch has multiple integrated poles and an internal fault affects all circuits).
• Torque Converter Clutch (TCC) remaining engaged when it should disengage, or engaging erratically.
• In some advanced systems, impact on ABS or stability control functionality.

What Causes the Code P0572?

• Faulty Brake Pedal Position Switch (BPPS): The most common cause, where the internal contacts of the switch are shorted, stuck in the “closed” (activated) position, or the switch itself has failed internally, sending a constant low voltage signal to the PCM.
• Wiring Harness Issues: A short to ground within the wiring harness leading to or from the brake switch ‘A’ circuit, or chafed, damaged, or corroded wires that create an unintended ground path.
• Corroded or Loose Electrical Connectors: Poor electrical connection at the brake switch connector or at the PCM connector, leading to high resistance or an intermittent short to ground.
• Improperly Adjusted Brake Pedal Position Switch: If the switch is physically misadjusted or incorrectly installed, it may not fully release when the pedal is not depressed, causing it to remain in an “activated” or “closed” state and send a low signal.
• PCM Failure: While rare, an internal fault within the Powertrain Control Module itself could cause it to incorrectly interpret the brake switch signal or to internally short the circuit. This is typically a last resort diagnosis after ruling out all other possibilities.

How to Diagnose and Troubleshoot

Diagnosis of P0572 requires a systematic approach using a digital multimeter (DMM), an OBD-II scanner with live data capabilities, and thorough visual inspection.

1. Initial Scan and Live Data Analysis: Connect an OBD-II scanner to the vehicle’s DLC. Confirm P0572 is the primary code. Check for any related or accompanying DTCs. Access the live data stream and monitor the parameter for the Brake Pedal Position Sensor/Switch (often labeled as BPPS, Brake Switch, or Cruise Control Brake Input). Observe its status (ON/OFF, or voltage reading) with the brake pedal both depressed and released. If the scanner consistently shows the switch as “ON” or a low voltage when the pedal is released, this corroborates the P0572 code.
2. Visual Inspection: Perform a thorough visual inspection of the brake pedal assembly. Verify that the brake pedal returns fully to its resting position. Locate the brake pedal position switch, typically mounted on the pedal bracket. Check for any physical damage to the switch, its wiring harness, or the connector. Look for signs of chafing, corrosion, or wires that are pulled taut or appear melted. Ensure the switch plunger or actuator is making proper contact with the brake pedal arm and is fully released when the pedal is not pressed.
3. Brake Switch Adjustment Check: Consult the vehicle’s service manual for the correct adjustment procedure for the BPPS. Incorrect adjustment can cause the switch to remain partially or fully activated.
4. Digital Multimeter (DMM) Testing at the Brake Switch:
   • Disconnect the brake switch connector. Refer to the vehicle’s wiring diagram to identify the power, ground, and signal wires for the ‘A’ circuit.
   • Check for Power Supply: With the ignition ON, use the DMM to check for battery voltage (B+) at the power supply wire terminal within the connector. If no voltage, diagnose upstream power supply issues (fuse, relay, wiring).
   • Check for Ground: Measure continuity or resistance between the ground wire terminal within the connector and a known good chassis ground. Expect very low resistance (near 0 ohms).
   • Test Switch Continuity/Resistance: With the switch disconnected, use the DMM’s continuity or resistance setting to test the switch directly. Operate the brake pedal through its full range. The ‘A’ circuit switch should typically show an open circuit (or very high resistance) when the pedal is released and continuity (or very low resistance) when depressed (or vice versa, depending on normally open/normally closed design). A constant low resistance or continuity when the pedal is released indicates an internal switch failure.
   • Test Signal Wire for Short to Ground: Reconnect the switch to its connector. Back-probe the signal wire at the brake switch connector (or disconnect the PCM connector and test the signal wire there). With the ignition ON and brake pedal released, measure the voltage on the signal wire. If the PCM expects a high voltage (e.g., 5V or B+) and you read near 0V, this confirms the ‘Circuit Low’ condition. Then, disconnect the switch and measure resistance from the signal wire terminal on the vehicle harness (leading to the PCM) to a known good chassis ground. Any reading significantly below infinity (e.g., less than 10k ohms) suggests a short to ground in the wiring.
5. Wiring Integrity Check (Switch to PCM): If all inputs to the switch are good and the switch itself tests correctly, the fault may lie in the wiring between the brake switch and the PCM. Disconnect both the brake switch connector and the PCM connector. Use the DMM to check for continuity on the signal wire between the two connectors. Also, check for shorts to ground and shorts to power on this wire.
6. Wiggle Test: While monitoring the live data for the brake switch, gently wiggle wiring harnesses and connectors, especially near the brake pedal, along the chassis, and at the PCM. Look for any momentary changes in the switch status that might indicate an intermittent connection or short.

Recommended Repairs and Solutions

Once the diagnostic steps have pinpointed the root cause, the following repairs are typically recommended:

1. Replace the Brake Pedal Position Switch (BPPS): This is the most common repair for P0572. Ensure that the replacement switch is an exact OEM equivalent or a high-quality aftermarket part. Follow the manufacturer’s specific installation and adjustment procedures carefully. Improper adjustment can lead to recurring codes or improper system function.
2. Repair Wiring Harness: If a short to ground or an open circuit is found in the wiring harness, the damaged section of the wire must be repaired or replaced. Use proper automotive wiring repair techniques, including soldering connections and using heat-shrink tubing for insulation. Avoid simply taping over damaged wires.
3. Clean or Replace Corroded Connectors: If corrosion or loose pins are identified at the brake switch or PCM connector, clean the terminals thoroughly using electrical contact cleaner and a small brush. If the corrosion is severe or pins are damaged, replace the affected connector. Ensure all connections are secure and free of debris.
4. Adjust Brake Pedal Position Switch: If the code was caused by improper switch adjustment, correctly adjust the switch according to the vehicle’s service manual specifications. This often involves adjusting the length of the plunger or the position of the switch on the pedal bracket.
5. PCM Replacement/Reprogramming: Only after all other diagnostic avenues have been exhausted and verified, and a definitive internal PCM fault has been identified, should PCM replacement or reprogramming be considered. This is a rare occurrence for P0572 and should not be pursued without conclusive evidence.

After any repair, clear the DTCs using an OBD-II scanner, perform a thorough test drive under various conditions, and re-scan the system to ensure the code does not return. Verify the proper operation of cruise control, brake lights, and any other systems affected by brake pedal input.