Brake Switch A Circuit High Input
The brake switch A signal is reading higher than expected.
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What it means (plain English)
The brake switch is supposed to signal when you press the brake, but it’s stuck in an 'on' state, sending too much voltage (usually above 5 volts) to the computer, making it think the brakes are always applied.
What the computer is actually seeing
The vehicle's computer expects the brake switch A to read below 5 volts when not pressed and around 0 volts or close to ground when pressed. If it sees above 5 volts continuously, it triggers the C0593 fault code.
What a healthy reading looks like
Brake switch A should read less than 0.5 volts when pressed and around 5 volts when released.
Guided diagnostic — the DiagCoach way
Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.
- 11. Inspect the brake switch and its connector for damage or corrosion. Fix any found issues.
- 22. Use a multimeter to check the voltage at the brake switch. It should be around 0 volts when pressed and close to 5 volts when not pressed. If it reads over 5 volts, proceed to step 3.
- 33. Check the wiring harness for short circuits or damaged insulation. Repair any issues found. Test again.
- 44. If the voltage readings are normal, replace the brake switch.
- 55. Clear the code and monitor for reoccurrence.
Common causes
- Faulty brake switch
- Wiring issues in the brake switch circuit
- Corroded connectors
- Short circuit in the wiring
- Faulty brake control module
Typical repair cost
$$$
Related codes
Frequently asked questions
Can I drive the vehicle with this code?
Yes, but be aware that the brake lights may stay on constantly, which can drain the battery.
Will this code trigger a check engine light?
Yes, this code typically lights up the check engine light or a brake system warning.
Why does this code come back after clearing?
If the underlying issue isn't resolved, like a faulty switch or wiring fault, the code will reappear.
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