1997 Acura CL check engine light

Hi jackmehoff,

Here you are.

DTC P0420: CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD
NOTE: If DTCs P0137, P0138 and/or P0141 are set at the same time as DTC P0420, trouble shoot those DTCs before trouble shooting DTC P0420.

1 . Perform PCM reset procedure. Start engine and run at 3000 RPM with no loads and transmission in Park or Neutral until cooling fan comes on. Connect SCS service connector.

Test drive vehicle at 40 - 55 MPH for about 2 minutes. Decelerate for at least 3 seconds with throttle fully closed. Reduce vehicle speed and hold at 35 MPH until readiness code comes on. If DTC P0420 resets, go to next step. If DTC P0420 does not reset, problem is intermittent, system is functioning properly at this time.

2 . Inspect Three-Way Catalytic Converter (TWC) for plugging, melting, cracking, exhaust system leaks or TWC deterioration. Repair or replace as necessary.

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