By iCarsoft Official Store Technical Team, Automotive Diagnostics Editors · Updated September 27, 2026 · Technical sources checked
Quick Answer
The C0023 code identifies stop lamp control in NHTSA's selected chassis-code reference. Apply this guide only when the vehicle's full OEM wording agrees. It does not prove a defective brake switch, a failed ABS hydraulic unit or a bad lamp by itself. Save the reporting module, suffix and event data, then follow the matching diagnostic branch.
What Does the C0023 Code Mean?
NHTSA's braking-system appendix lists C0023 as Stop Lamp Control with a subfault. This guide applies when the VIN-specific OEM description agrees. The full fault record determines the test branch.
Stop-lamp control connects a brake request with the external brake lights. A switch input, controller-driven output and network-delivered brake request are different paths. Identify which path the reporting module monitors before choosing a measurement.
Actual lamp operation and controller data must be compared, not substituted for one another. Record the pedal request seen by each relevant module and the observed lamp response. If a lamp stays on or fails to illuminate, follow that physical circuit. If the lamps respond normally but inputs disagree, inspect the specific signal and module path named by the full fault.
NHTSA’s chassis-code appendix names C0023 Stop Lamp Control and leaves the subfault to the implementation. That wording does not specify a universal switch adjustment, lamp-current limit or relay location. Use the vehicle’s complete fault text to distinguish an electrical output problem from disagreement between brake-request inputs or related module messages.
A brake light can illuminate while another module still reports an implausible request, and an illuminated dashboard display does not prove the rear lamps work. Confirm the external lamps with the vehicle safely secured. If the event followed a switch or lamp replacement, check the exact part, connector and installation steps rather than assuming the timing proves causation.
Save the full module wording and suffix before clearing; they can change the test path.
Separate C0023 from adjacent fault families
| Code | General description | Key distinction |
|---|---|---|
| C0023 | Stop Lamp Control | Control/output label with implementation-specific subfault. |
| P0504 | Brake Switch A/B Correlation | Agreement between named input paths. |
| P0571 | Cruise Control/Brake Switch A Circuit | A related circuit family with its own test procedure. |
| C0040 | Brake Pedal Switch A | Standardized chassis input label; OEM mapping still matters. |
Record the complete C0023 description. The suffix, reporting module and companion faults can change the diagnostic path. Use the manufacturer's full wording and test procedure for the exact vehicle.
C0023 Symptoms and Likely Causes
Record C0023 symptoms and fault status; symptoms alone cannot identify a failed part.
Check whether companion faults share a proven cause.
The external brake lights may not illuminate when commanded. This is a traffic-safety problem even if the hydraulic brakes otherwise appear to stop the vehicle.
A stuck request, incorrect installation or an output-path problem can keep the lamps illuminated. Continuous illumination prevents following traffic from distinguishing a new braking event.
ABS, stability or other control warnings may accompany disagreeing brake information. Their presence does not automatically establish a hydraulic fault.
Functions that use a brake request may behave differently on some vehicles. Diagnose those symptoms by the actual wiring and module information, not by assuming one shared switch fixes everything.
Practical cause-checking order
- Identify the full event: Save the complete module and suffix so stop-lamp output faults are not confused with input correlation or network faults. Confirm which controller detected the inconsistency.
- Check the connections: Inspect the switch and lamp connectors, grounds and accessible wiring, including recent trailer equipment or rear-body repairs where relevant. Use only approved electrical test points.
- Test the relevant circuit: Check the actual pedal request and output state under the prescribed conditions. Compare a scan-tool status with a meter or other approved physical test where the procedure calls for it.
- Check the physical counterpart: Check compatible lamp assemblies and switch installation against the parts and adjustment procedure. Do not bypass an electronically monitored output with an improvised load.
- Confirm the final repair branch: Consider a controller output or software issue only after the defined external checks pass and an applicable OEM procedure supports that branch.
Did C0023 appear after recent brake-switch, pedal, rear-lamp, trailer-wiring or battery work? Recheck the documented connections, parts and setup steps affected by that work. Record battery and software history; a post-repair code does not prove the new part is defective.
How Serious Is C0023, and Can You Drive?
Do not drive in traffic with brake lights that fail or stay on continuously. Check them with the vehicle secured. Follow the owner manual; abnormal pedal feel, fluid loss or a red brake warning warrants stopping safely and arranging recovery. A code cannot establish safe driving distance.
Record brake warnings, pedal changes, fluid loss and recent service. Do not induce wheel slip or emergency braking to test assistance on public roads; warning-state assessment comes before any functional verification.
Stop and arrange a tow if brake lamps fail or remain on, pedal feel changes, fluid leaks or a red brake warning appears.
Brake systems may retain pressure or operate electrically after the engine stops. Follow the exact shutdown and pressure-release procedure before opening anything. Support a raised vehicle on approved equipment, keep hands away from moving parts, and do not energize unidentified brake circuits with jumper wires. A public-road emergency stop is not an acceptable diagnostic experiment.
How to Diagnose C0023 in the Right Order
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Save the event and check the external brake lamps
Secure the vehicle, record the complete C0023 fault, and save companion codes and available conditions. Check whether the brake lamps respond to the pedal, remain on or fail intermittently. Keep lamp observations separate from dashboard icons. Do not drive in traffic with a known brake-light failure while collecting more evidence.
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Identify the monitored request or output
Identify the reporting ABS, body or other module and read its full suffix-specific description. Obtain the correct diagram showing the brake request, any network message and the lamp output. A circuit monitored by one controller may not be the same as the scan PID shown by another. Use the OEM test for that exact path.
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Inspect recent switch and lighting work
Review brake-switch replacement, pedal work, lamp changes and trailer wiring. Inspect safely accessible connectors, terminal fit and harness routing. Follow the prescribed installation or adjustment procedure if the switch was disturbed; arbitrary repositioning can create another fault or alter other brake-dependent functions. Document the observation before altering the setup.
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Compare pedal input with controller data
With the vehicle stationary and all prerequisites met, compare supported pedal or brake-switch data with the actual pedal state. Note which module supplies each PID and whether its state changes as expected. Where the procedure requires electrical measurement, verify at the approved test point rather than treating a displayed status as physical proof.
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Test the output and lamp circuit safely
Trace the commanded output through the specified fuse, wiring, connector, return and lamp assembly. Electronically protected drivers require the correct meter or load-test method; an improvised test lamp can be inappropriate. Do not bridge a controller pin or install a resistor to make the fault disappear without correcting its cause.
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Confirm lamp behavior and related control functions
Repair the failed path and perform any required setup. Verify normal brake-light response, safe braking and applicable brake-dependent functions. Clear erasable records only after saving evidence, then repeat the OEM confirmation check. If lamps work but C0023 returns, compare the module and suffix rather than repeatedly changing bulbs or switches.
Specifications are vehicle-specific. Use the exact VIN specifications, approved test points and required operating state. No generic value or drive cycle can replace the applicable procedure. Manufacturer examples here do not establish specifications for other applications.
C0023 Repairs and Cost Planning
A C0023 repair must address the demonstrated failure. Do not replace an assembly from the code alone.
Recheck installation and required setup after repair. A repair may involve a connection, switch installation, compatible lamp assembly or a proven control output. Modern lighting circuits may be monitored electronically; do not fit a resistor, bypass relay or altered bulb load to silence the code. Restore the specified configuration and verify both lamp operation and the related brake-request data.
Ask the shop to name the failed branch and the measurement supporting each proposed repair.
Authorize diagnosis before parts while the cause remains uncertain.
| Possible path | Quote basis |
|---|---|
| Repair the connector or harness after a documented circuit failure | VIN-specific quote |
| Correct the demonstrated physical or installation fault | VIN-specific quote |
| Replace only the component that fails its prescribed test | VIN-specific quote |
| Complete required setup and safe functional verification | VIN-specific quote |
These are alternative repair paths, not prices to add together. Request a VIN-specific quote separating diagnosis, parts, labor, fluids, taxes, required setup and verification. Ask which failed test supports the proposed repair and whether warranty coverage applies.
Using iCarsoft CR Eagle P for C0023
On a supported vehicle, iCarsoft CR Eagle P can save accessible faults, available freeze frame, live data and diagnostic reports. Preserve the C0023 evidence before clearing.
Compare available brake-controller records before and after repair. The report supports diagnosis but cannot replace the OEM physical and functional checks.
Preserve the stop-lamp control and brake-request agreement evidence
iCarsoft CR Eagle P
Review supported codes and relevant live data together. Confirm the exact VIN, controller access, PIDs and any requested active test with iCarsoft before purchase; generic product capabilities do not guarantee a C0023-specific function.
Check current CR Eagle P price and availabilityCheck CR Eagle P compatibility by VINThe official product page describes supported full-system diagnostics, available live data, freeze frame and diagnostic reports; exact controller coverage and active tests depend on the VIN and software. Confirm the requested function by VIN before purchase. Follow OEM prerequisites and stop for abnormal operation.
Know the measurement boundary. Scan data describes ECU-provided information; it does not directly prove the physical condition of the stop-lamp control and brake-request agreement. Where required, use the specified multimeter, oscilloscope and approved brake-system test equipment and compare reported values with the relevant measured evidence.
Verify the C0023 Repair
After repair, verify connectors, harness clearance, setup and controller supply. Save post-repair findings, then clear only erasable records through the approved procedure. Battery disconnection is not a repair.
Run the manufacturer's applicable verification conditions in a safe workshop or route. Compare the original operating state with current data for the stop-lamp control and brake-request agreement, and check current and pending faults in related modules. One clean start or idle period does not prove that every conditional monitor has completed.
Compare the original and final scans, including fault status, operating conditions and required setup. Record whether the monitor completed and whether the original event returned.
If C0023 returns, compare its suffix, status, failure order and operating conditions with the saved baseline before replacing another part. Revisit the failed branch and inspect anything disturbed. Confirm the prescribed brake-system verification separately from code clearing.
Stored and Active brake-control faults require different decisions. Preserve the original record and follow the OEM confirmation procedure. A cleared display does not prove restored assistance or safe braking.
Related Stop-Lamp Control And Brake-Request Agreement Code Guides
Compare the related monitor families below. Shared symptoms or components do not make their repair procedures interchangeable.
C0023 Frequently Asked Questions
Does the C0023 code mean the named component is bad?
No. In the reference mapping, C0023 identifies stop lamp control with a subfault. First confirm the OEM wording for the reporting module. The code does not prove a defective brake switch, a failed ABS hydraulic unit or a bad lamp by itself; the suffix and prescribed tests determine the failed branch.
What should I check first for C0023?
Save every module's codes and freeze frame before clearing. Confirm the full definition, suffix and VIN architecture. Then inspect recent brake-switch, pedal, rear-lamp, trailer-wiring or battery work, connectors and shared supplies. Those facts determine whether the next test needs the specified multimeter, oscilloscope and approved brake-system test equipment or a manufacturer-specific functional procedure.
Can I drive with the C0023 code?
Do not drive in traffic with brake lights that fail or stay on continuously. Check them with the vehicle secured. Follow the owner manual; abnormal pedal feel, fluid loss or a red brake warning warrants stopping safely and arranging recovery. A code cannot establish safe driving distance.
Why did C0023 return after a part was replaced?
Recheck pedal-switch seating or adjustment only by the applicable service instructions, and inspect anything disturbed around the lamps or trailer connection. An incorrect replacement part or unresolved wiring problem can remain after a code is cleared. Match the returning suffix before deciding whether the original problem or a different branch has returned.
What should a C0023 repair estimate include?
Ask for the failed-test evidence and a VIN-specific breakdown of diagnosis, parts, labor, taxes, required setup and verification. A code alone cannot establish the repair price.
Can CR Eagle P diagnose and clear C0023?
On a supported vehicle, CR Eagle P can organize available faults, freeze frame, live data and reports, and can clear erasable records after repair. Confirm exact ECU coverage. It cannot establish safe braking from an erase command or replace physical measurements for the stop-lamp control and brake-request agreement.
The iCarsoft Official Store Technical Team maintains the store's fault-code library. This guide organizes published technical references and verified product information; it does not document a hands-on test of a particular vehicle or claim an individual engineer's review.
Technical and cost references
- NHTSA DOT HS 812 574 — Hydraulic Braking System Appendices. March 2018; Appendix K, Table K-2 provides selected chassis-code labels. It does not replace current VIN-specific service information.
Product information: Official iCarsoft CR Eagle P page.
Editorial note: General diagnostic education, not a substitute for the owner's manual, current VIN-specific service information or professional inspection. Test limits, procedures, coverage and costs vary. Related articles provide context; apply only the specifications and repair procedures that match the vehicle. No universal failure rate, repair price or outcome is implied.
