P1577 Brake Switch Circuit Malfunction
The P1577 code indicates that the Powertrain Control Module (PCM) has detected an electrical fault in the brake on/off (BOO) switch circuit. This occurs when the brake switch signal fails to change state as expected (e.g., stuck high or low), reads out of range, or does not correlate with accelerator pedal position (APP) sensor and vehicle speed data during driving.
01. Most Common Causes
- Faulty or misadjusted brake pedal switch (BOO)
- Open, short-to-ground, or short-to-voltage in the brake switch circuit wiring
- Corroded, loose, or damaged connectors at the brake switch or PCM
- Blown fuse in the brake switch power circuit
- Internal PCM failure (rare)
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Brake lights may not function properly
- Cruise control may be disabled
- Harsh or delayed transmission shifting
- Reduced engine power or limp mode
03. Step-by-Step Diagnosis
Verify the code and check for related codes (e.g., P0703, P0504).
Inspect brake lights operation; if inoperative, check fuse and bulbs.
Visually inspect brake switch for proper adjustment and physical damage.
Test brake switch signal with a scan tool or multimeter: should change state when pedal is pressed.
Check wiring and connectors for corrosion, damage, or poor contact.
If all else passes, suspect PCM fault and perform further testing.
1. Frequently Asked Questions
Is it safe to drive?▼
You can usually drive short distances, but the vehicle may have reduced functionality (e.g., no cruise control, harsh shifting). Have it diagnosed soon to avoid potential safety issues.
How much does it cost to fix?▼
Typically $100–$250 for a brake switch replacement, including parts and labor. Wiring repairs or PCM replacement can cost more.