OBD-II code C0023 indicates a fault in the stop lamp (brake light) control circuit as detected by a control module, most often the ABS module or the PCM. The code is set when the module sees a signal from the stop lamp switch or the lamp circuit that is out of the expected range, such as no signal when the pedal is pressed, a stuck signal, or abnormal voltage in the circuit.
The mechanical switch that signals brake pedal position wears out or becomes misadjusted. This is by far the most common cause and is usually a low-cost, easily accessed part.
The stop lamp circuit passes through connectors near the pedal assembly and the rear lamp housings. Chafed wires, loose pins, or green corrosion at connectors can produce the same fault signature as a bad switch.
A blown fuse or a shorted brake light bulb can drop the circuit voltage and set the code. Bulb failure is more common on vehicles that have not had the rear lamps serviced in years.
If the pedal does not return fully or the switch mount is loose, the switch may not make proper contact. This produces a stuck-on or stuck-off signal that mimics a bad switch.
The module reads the stop lamp circuit to enable ABS pump operation and other functions. Internal input circuitry on the module can fail, but this is uncommon compared with switch and wiring faults.
The PCM is sometimes listed as a possible cause because it receives brake switch data. In real-world practice, the PCM itself is almost never the reason for a C0023 and should be considered only after every other cause has been ruled out.
Yes. A shorted or open bulb changes the resistance the module sees on the circuit, and on many vehicles this alone will set C0023. It is worth checking the bulbs before buying any parts.
It is almost always the brake light switch or the wiring around it. The PCM is occasionally listed as a possible cause, but in real-world service the switch and its circuit are the source of the code in the large majority of cases, and the computer is essentially never the root cause.
Generally the vehicle can still be driven, but brake lights may not function correctly, which is a significant safety and legal problem, and features like cruise control or ABS behavior may be affected. Repair should be prioritized rather than postponed.
No. Clearing the code only erases the stored fault. If the underlying condition, such as a bad switch or broken wire, is still present the code will return, usually within a single drive cycle.