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2023 GMC SIERRA 2500HD
6.6L V8 L8T•4WD•AUTOMATIC•gas•turbo
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Repairs0Labor503Torque1488Fluid10DTC2017Battery1Maintenance0Recalls0
B0420moderate severityBody

Check Engine Lamp Circuit

on 2023 GMC Sierra 2500HD 6.6L V8 L8T · 4WD

What this code means

Malfunction in the check engine/MIL indicator lamp circuit in the instrument cluster.

Symptoms

  • Check engine light does not illuminate during bulb check
  • Light stays on with no DTC stored
  • Light flickering
  • Cannot determine if engine codes are present

Common causes

  • Burnt out MIL bulb/LED
  • Cluster circuit board fault
  • Wiring from PCM to cluster damaged
  • PCM MIL driver failure

Diagnostic steps

  1. Check bulb during key-on bulb check
  2. Test MIL drive circuit from PCM
  3. Inspect cluster wiring
  4. Scan PCM for codes
  5. Test cluster LED

Repair notes

Replace MIL bulb/LED in cluster or repair wiring from PCM to cluster.

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