Brake Switch “A” Circuit Low: Complete Diagnostic & Repair Guide
Code Definition
P0572 indicates that your vehicle’s Powertrain Control Module (PCM) has detected a lower than expected voltage or a constant “low” signal from the Brake Switch “A” circuit. Essentially, your car’s computer believes the brake pedal is never being pressed, regardless of its actual position.
The P0572 diagnostic trouble code (DTC) is a common issue that affects the brake switch circuit in vehicles. At 24car-repair.com, we provide comprehensive, detailed guides to help you understand and resolve automotive issues efficiently. This extensive article covers everything from the fundamental principles behind the P0572 code to advanced diagnostic procedures and cost-effective repair solutions tailored for Mers-market vehicles.
Symptoms of P0572 Code
When the P0572 code is stored in your vehicle’s PCM, you may experience one or more of the following symptoms, which can vary in severity depending on the underlying cause:
- Illuminated Check Engine Light (CEL) or Malfunction Indicator Lamp (MIL) – This is always present when the code is active
- Cruise control system inoperative – The system may refuse to engage or may disengage unexpectedly while driving
- Brake light malfunction – Either the brake lights remain illuminated constantly, or more dangerously, they fail to illuminate when the brake pedal is pressed
- Difficulty shifting out of Park – Automatic transmission vehicles may prevent gear selection without brake pedal application
- Push-to-start ignition issues – Modern vehicles with keyless ignition may not start as the system doesn’t detect brake pedal application
- Unexpected transmission behavior – Some vehicles may experience harsh shifting or limited performance modes
- Additional related codes – You may also find codes such as P0570, P0571, or P0573 stored in the PCM
Is It Safe to Drive With a P0572 Code?
Before considering driving your vehicle, perform this comprehensive safety assessment:
- Park your vehicle on level ground with the engine running and parking brake engaged
- Have an assistant stand behind the vehicle to observe all brake lights (including the high-mounted third brake light)
- Press and release the brake pedal multiple times, verifying that all lights illuminate brightly and consistently
- Check that the lights turn off completely and immediately when the brake pedal is released
- Test the cruise control system in a safe environment to verify it engages and disengages properly
If your brake lights show any inconsistency or complete failure, do not drive the vehicle until the issue is resolved. Arrange for towing to a repair facility if necessary. Even if the brake lights appear functional, the underlying issue could worsen suddenly while driving.
Common Causes of P0572 Code
The P0572 code can be triggered by several electrical issues, ranging from simple to complex. Understanding these causes will help you diagnose the problem efficiently:
Faulty Brake Light Switch
This is the most prevalent cause, accounting for approximately 65-70% of P0572 cases. The brake light switch, typically located at the top of the brake pedal arm, contains internal contacts that complete the circuit when the pedal is pressed. Over time, these contacts can wear out, become contaminated, or the switch mechanism can fail, preventing proper circuit operation.
Blown Fuse or Fusible Link
The brake light circuit is protected by one or more fuses. A blown fuse will interrupt power to the brake switch, causing the P0572 code. Common fuse locations include the interior fuse panel (typically near the driver’s side dashboard) and the under-hood fuse box. In some vehicles, a fusible link in the engine compartment may serve this purpose.
Damaged Wiring or Connectors
The wiring harness connecting the brake switch to the PCM can become compromised due to:
- Heat degradation from prolonged exposure to engine compartment temperatures
- Chafing or abrasion against sharp metal edges or moving components
- Rodent damage – wiring insulation is attractive to rodents for nesting material
- Corrosion from moisture – particularly problematic in humid Mers climates or vehicles with water leakage issues
- Previous repair damage – poor electrical repairs can lead to future failures
Faulty Cruise Control Switch
On many vehicle models, particularly older designs, the brake switch works in conjunction with or is integrated into the cruise control cancel switch. A malfunction in this integrated system can trigger the P0572 code even if the primary brake switch function appears normal.
Failed PCM (Rare)
In rare instances (less than 5% of cases), the Powertrain Control Module itself may be malfunctioning and not properly interpreting the signal from the brake switch. This should only be considered after all other potential causes have been systematically eliminated through proper diagnostic procedures.
P0572 Repair Cost Estimate
Repair costs for P0572 vary significantly based on your vehicle’s make and model, the root cause of the problem, and labor rates in your specific area of Mers. Here’s a comprehensive breakdown of potential costs with detailed explanations:
| Repair Procedure | Parts Cost (USD) | Labor Cost (USD) | Total Estimated Cost (USD) | DIY Difficulty & Time |
|---|---|---|---|---|
| Replace Brake Light Switch Most common repair – involves replacing the faulty switch assembly |
$15 – $50 OEM parts at higher end |
$50 – $120 0.5 – 1 hour at $100/hr |
$65 – $170 |
Easy DIY Friendly
|
| Replace Fuse Simple fuse replacement – lowest cost solution |
$5 – $10 Fuse pack typically $5-10 |
Included in diagnostic Typically no separate charge |
$5 – $10 |
Very Easy Beginner
|
| Repair Wiring/Connector Complex repair involving wire repair or connector replacement |
$20 – $80 Wire, connectors, loom |
$100 – $250 1 – 2.5 hours at $100/hr |
$120 – $330 |
Moderate Intermediate
|
| Replace PCM/ECU Most extensive repair – module replacement and programming |
$500 – $1,000+ New module + programming |
$150 – $300 1.5 – 3 hours at $100/hr |
$650 – $1,300+ |
Hard Professional
|
Step-by-Step Diagnostic Guide
Follow this comprehensive diagnostic procedure to accurately identify the cause of your P0572 code. Always prioritize safety and consult your vehicle’s service manual for specific details about your model.
Preliminary Safety Checks
Begin with these essential safety verifications before starting detailed diagnostics:
- Verify the brake lights are functioning properly through comprehensive testing
- Check if the cruise control system engages and disengages correctly
- Note any other symptoms or related codes that may provide additional clues
- Ensure the vehicle is parked on a level surface with the parking brake engaged
Locate the Brake Light Switch
The brake light switch is typically mounted on the brake pedal bracket, near the top of the pedal arm. In most vehicles, it’s accessible from the driver’s footwell without removing any panels. Consult your vehicle’s service manual for the exact location and access procedure for your specific model.
Inspect the Fuse
Locate the brake light fuse in your vehicle’s fuse box (check both interior and engine compartment fuse boxes). Use the fuse diagram on the fuse box cover to identify the correct fuse. Remove the fuse and visually inspect it for a broken filament. Test with a multimeter for continuity if visual inspection is inconclusive.
Test the Brake Light Switch
Using a digital multimeter, test the brake light switch for proper operation:
Inspect Wiring and Connectors
Carefully examine the entire wiring harness connected to the brake switch, following it as far as possible toward the PCM. Look for:
- Frayed, cracked, or damaged insulation
- Corroded, loose, or bent connector pins
- Signs of overheating, melting, or previous repairs
- Proper connector seating and locking mechanisms engaged
Clear Codes and Test Drive
After making repairs, clear the DTCs with your scan tool. Perform a test drive that includes various driving conditions: city streets, highway cruising, and multiple brake applications. Verify that the code does not return and all systems are functioning normally.
Frequently Asked Questions (FAQ)
While it may be tempting to drive if the brake lights appear functional, we still don’t recommend extended driving with an active P0572 code. The issue could be intermittent or could worsen suddenly while driving. Additionally, other systems like cruise control may not function properly, and the underlying electrical issue could affect other vehicle systems. The safest approach is to diagnose and repair the issue promptly.
Dealership repairs typically cost 20-40% more than independent shops for the same repair. A brake light switch replacement at a dealership might cost $120-$220, while an independent shop might charge $80-$160. For more complex wiring repairs, dealerships might charge $300-$450 compared to $200-$350 at independents. Always get multiple quotes if possible, and consider that dealerships may have more specific knowledge of your vehicle model.
For most vehicles, you’ll need:
- Basic socket set (typically 8mm, 10mm, 13mm sockets)
- Screwdrivers (Phillips and flat-head)
- Pliers (needle-nose are helpful)
- Flashlight or work light
- Multimeter for testing (optional but recommended)
- Vehicle-specific trim removal tools (for some models)
Always consult your vehicle’s repair manual for specific tool requirements and safety precautions.
Push-button ignition systems require confirmation that the brake pedal is pressed before allowing the engine to start. This is a safety feature to prevent accidental vehicle movement. If the PCM receives an incorrect signal from the brake switch (indicating the brake isn’t pressed), it will prevent the engine from starting, assuming the driver isn’t properly prepared to operate the vehicle.
Yes, in most regions including Mers, an active P0572 code will likely cause your vehicle to fail emissions or safety inspection for several reasons:
- Check Engine Light is illuminated (automatic failure in most inspections)
- Brake light functionality is checked during safety inspection
- Cruise control malfunction may be noted if tested
- The code indicates an electrical system fault that affects safety systems
It’s advisable to repair the issue before taking your vehicle for inspection to avoid failure and re-inspection fees.
Conclusion
The P0572 diagnostic trouble code is a common but serious issue that directly impacts safety-critical systems in your vehicle, particularly the brake lights. For most Mers-market vehicles, the solution involves replacing an inexpensive brake light switch, which is often a straightforward repair.
We recommend starting with the simplest and most cost-effective diagnostic steps (checking fuses, visually inspecting the brake switch and wiring) before progressing to more complex procedures. Always prioritize safety—if you’re unsure about any aspect of the diagnosis or repair, consult a qualified automotive technician.
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