C0023
Stop Lamp Switch Circuit Malfunction
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The C0023 code means the vehicle's control module has detected a problem with the brake light (stop lamp) switch circuit. The brake light switch serves multiple critical functions beyond just turning on your brake lights — it also signals the ABS module, disengages cruise control, allows the transmission to shift out of Park, and communicates with the stability control system. A malfunction here can cascade into multiple vehicle systems.
The most immediate safety concern is that other drivers behind you may not see your brake lights when you slow down or stop, dramatically increasing the risk of being rear-ended. Additionally, cruise control may not work, and on automatic transmissions, you may have difficulty shifting out of Park. Some vehicles may also disable ABS or stability control when the brake switch signal is unreliable.
The good news is that this is often one of the simpler and less expensive chassis repairs. The brake light switch is typically located above the brake pedal and can often be replaced in under 30 minutes. Check the obvious things first — blown fuses and burned-out brake light bulbs — before replacing the switch. If you're comfortable working under the dashboard, this is a very doable DIY repair with an inexpensive part.
Severity
Symptoms
- •Brake lights not turning on when pressing the brake pedal
- •Brake lights staying on constantly even when the pedal is released
- •Cruise control not engaging or disengaging unexpectedly
- •Vehicle may not shift out of Park on automatic transmissions
- •ABS or stability control warning lights on the dashboard
Likely Causes
The brake light switch is a small mechanical or electronic switch mounted near the brake pedal that activates when you press the pedal. Internal contacts can wear out, corrode, or break, causing it to send incorrect signals or no signal at all.
The switch must be precisely positioned relative to the brake pedal arm. If the mounting clip breaks, the switch pedal stopper pad deteriorates, or the switch shifts position, it may not activate at the correct pedal travel point.
The wiring harness that connects the brake light switch to the body control module and lighting circuits can develop breaks, shorts, or corroded connections due to moisture exposure in the driver's footwell area.
A blown fuse in the brake light circuit or a failed relay can prevent brake lights from functioning, and the ABS module may detect this as a stop lamp control fault.
Estimated Cost
Professional Repair
Includes parts + labor
Common Fixes
- Replace the brake light switch
- Adjust the brake light switch position on its mounting bracket
- Replace the brake pedal stopper pad that activates the switch
- Repair damaged wiring or corroded connectors at the switch