Clearing Trouble Codes

1990 Chevrolet Hi-Cube 7.4 N, 400/M40SECTION Clearing Trouble Codes

Trouble codes should be cleared after repairs have been completed. Also, some diagnostic charts require that codes be cleared before using diagnostic chart. To clear codes, remove ECM memory battery voltage for 30 seconds.

If no hard fault codes are present (only intermittent codes exist), proceed to H - TESING W/O CODES article for intermittent diagnostic procedures.

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • You smell fuel, burning insulation, or see smoke.
  • Brakes feel soft, pull hard to one side, or make grinding noises.
  • The engine overheats, stalls repeatedly, or misfires under load.
  • You are missing required tools, torque specs, or safe lifting equipment.
  • You are not confident in the next step or safety outcome.