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 DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 9 (ENGINE CONTROLS - TESTS W/CODES)DIAGNOSTIC TESTSDTC P0420: CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD
1998 Acura 3.5RL Special Edition
DTC P0420: Catalyst System Efficiency Below Threshold
1998 Acura 3.5RL Special EditionSECTION DTC P0420: Catalyst System Efficiency Below Threshold
WARNING: This page is about a different car, the 1998 Acura 2.3CL. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
If DTCs P0137, P0138 and/or P0141 are set at same time as DTC P0420, trouble shoot those DTCs before trouble shooting DTC P0420.
- 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 cooling fan comes on. Connect SCS service connector. See Figure. 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.
- 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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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.