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Home / DTC / C1223 — Lamp Brake Warning Output Circuit Failure

C1223 — Lamp Brake Warning Output Circuit Failure

Detailed page for trouble code C1223.

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Code

C1223

Generic C — Chassis

Lamp Brake Warning Output Circuit Failure

Brand: Generic
Type: C — Chassis
Views: UK: 24 EN: 34 RU: 38
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Page language: EN

Causes

  • Blown fuse or faulty relay for brake/stop lamp circuit
  • Burned-out or intermittent brake/stop bulb(s)
  • Open or shorted wiring between module and lamp (chafe, cut, pinched)
  • Corroded or loose lamp socket or connector
  • Poor ground at lamp or module
  • Water intrusion in connector or lamp housing

Symptoms

  • Brake warning lamp or indicator illuminated on dash
  • Brake lights may be inoperative, dim, or intermittent
  • Related ABS/traction or brake-system messages may appear
  • Possible loss of trailer brake detection or incorrect warning
  • Codes present after clearing or reoccurring intermittently

What to check

  • Scan for stored and pending codes and view data/ freeze-frame
  • Visually inspect rear lamp sockets, bulbs, harness and connectors
  • Check fuses/relays for the brake lamp circuit
  • Command/flash brake lamps with scan tool (if supported) while watching voltages
  • Measure voltage at lamp socket with brake pedal pressed (expect ~battery voltage)
  • Check continuity and resistance between module output and lamp socket

Signal parameters

  • Output voltage: ~11–15 V (battery voltage) when lamp is commanded ON
  • OFF state: near 0 V (or module open/high impedance) at output
  • Lamp current (typical): ~0.5–3 A per filament depending on bulb type
  • Continuity: low resistance path between module output and lamp (~
  • Intermittent/erratic: fluctuating voltage or drop under load indicates high resistance connection or short

Diagnostic algorithm

  1. Read and record all stored/PID data for C1223. Note freeze-frame and whether lamp is commanded by a scan tool.
  2. Perform a visual inspection of bulbs, sockets, connectors, wiring and any aftermarket trailer/tow harness for damage or corrosion.
  3. Check relevant fuses and relays. Replace any blown fuses and retest.
  4. With a DVOM, measure voltage at the brake lamp socket while an assistant presses the brake pedal (or use scan-tool lamp command). Confirm ~battery voltage when ON and ~0 V when OFF.
  5. Measure continuity between module output pin and lamp socket pin with power removed. Repair any open or high-resistance sections found.
  6. Check ground integrity: measure voltage drop between lamp ground and battery negative while lamp is ON (should be very low). Clean/repair ground as needed.
  7. If voltage drops under load, measure current draw to detect short or overload. Isolate circuits (disconnect trailer harness, bulbs) to locate short.
  8. Wiggle-test connectors/wiring while observing output voltage or lamp operation to reproduce intermittent behavior.
  9. If wiring, bulbs, grounds, fuses and relays are good and wiring checks out, suspect output stage in ABS/BCM. Verify module outputs for other channels; consult manufacturer guidance before module replacement.
  10. After repairs, clear codes, re-scan, and perform a road or bench test to confirm fault does not return.

Likely causes

  • Blown fuse or bulb(s)
  • Corroded/loose connector at lamp or harness splice
  • Open/short in harness (chafe or damaged insulation)
  • High-resistance ground connection
  • Faulty module output when wiring and bulbs check good

Fault status

⚠️ Status
Brake lamp warning output circuit failure detected — open, short, intermittent or abnormal resistance in the brake lamp output circuit.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

C1220 C1221 C1222 C1224 C1250
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