Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSACURA19983.5RL SPECIAL EDITIONREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMENGINE CONTROLS - TESTS W/CODESDIAGNOSTIC TESTSDTC P0420: CATALYST EFFICIENCY BELOW THRESHOLD
1998 Acura 3.5RL Special Edition
DTC P0420: Catalyst Efficiency Below Threshold
1998 Acura 3.5RL Special EditionSECTION DTC P0420: Catalyst Efficiency Below Threshold
NOTE:
Trouble shoot DTC P0136, P0139 or P0141, if set, before proceeding.
- 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.
- Perform PCM reset procedure. See PCM RESET PROCEDURE/CLEARING CODES under SELF-DIAGNOSTIC SYSTEM. Start engine and run at 3000 RPM with no load and transmission in Park or Neutral, until radiator fan comes on. Install SCS Service Check Connector Tool (07PAZ-0010100 ). See Figure .
- 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.
- Remove TWC. Also remove WU-TWC. Shine a flashlight into catalyst inlet while looking into catalyst outlet. Check for plugging, melting or cracking. Replace TWC and/or WU-TWC if necessary.
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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.