LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Acura >> 1997 >> 3.2TL >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> Circuit Tests >> DTC P0420: Catalyst Efficiency Below Threshold
April 5, 2026: LEMON Manuals is launched! Read the announcement.

DTC P0420: Catalyst Efficiency Below Threshold

NOTE: If DTCs P0136, P0139 and/or P0141 are set at the same time as P0420, trouble shoot these DTCs before DTC P0420.
  1. If DTC P0420 is set, check Three-Way Catalytic Converter (TWC), check for exhaust system leakage. Repair or replace components as necessary. If no problems are found, go to next step.
  2. Perform PCM reset procedure. See PCM RESET PROCEDURE/CLEARING CODES  . Start engine and run at 3000 RPM with no loads and transmission in Park or Neutral, until radiator fan comes on. Install SCS Service Check Connector Tool (07PAZ-0010100 ). See Figure .
  3. Test drive vehicle at 40-55 MPH for at least 2 minutes. Decelerate with throttle completely closed for at least 3 seconds. Reduce speed to 35 MPH and try to hold it there until readiness code comes on. If DTC P0420 sets, go to next step. If DTC P0420 does not reset, problem is intermittent, system is okay at this time.
  4. Remove TWC. Shine a flashlight into catalyst inlet while looking into catalyst outlet. Check for plugging, melting or cracking. Replace TWC if necessary.
scientia non olet · About LEMON Manuals