TWC Monitor Test Counter

1999 Chevrolet Lumina V6-3.8L VIN KSECTION TWC Monitor Test Counter
Scan Tool Range 0 - 49. The TWC monitor test counter increments while the TWC system diagnostic test is running and taking samples. When the TWC Monitor Test Counter reaches 49, the PCM will update the TWC diagnostic statistical filter. At this point, the TWC Monitor Test Counter will reset to 0 and begin incrementing again. The TWC Monitor Test Counter is most useful when verifying a Three-way catalytic converter replacement or any repair associated with the DTC P0420 diagnostic table.
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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.