Applicable Systems
OBD-II
Symptoms
Brake light switch signal voltage high when brake not applied; ECM thinks brake is always pressed; cruise control disabled.
Possible Causes
- Brake light switch stuck closed
- Switch signal wire short to +12V
- Switch internally shorted
Troubleshooting Steps
- Step 1: Check brake light switch signal at key ON (brake released)
Signal low (brake not pressed) - Step 2: Check for brake lights staying on when pedal released
Brake lights off when pedal released - Step 3: Check switch signal wire for short to +12V
No short to +12V - Step 4: Replace brake light switch if stuck
Signal correct - Step 5: Clear code and verify operation
Cruise control functional
How to Reset
Clear with OBD-II scanner after repair.
Common Replacement Parts
- Brake Light Switch (OEM spec)
Frequently Asked Questions
- Q: Can faulty brake switch drain battery?
Yes, if switch stuck closed, brake lights stay on continuously and drain battery overnight.
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Source: SAE J2012 standard DTC list + OBD-II portal
Category: OBD-II
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