DTC P0420: Three-Way Catalyst (TWC) Efficiency Low
- Turn ignition off. Connect scan tool to Data Link Connector (DLC). Turn ignition on. Clear DTCs. Select READINESS TESTS mode on scan tool to monitor catalyst. Test drive vehicle at 35-45 MPH in 3rd gear (A/T or M/T) for at least 8 minutes. Slow vehicle speed to 30-40 MPH and hold for at least 2 minutes. Slow vehicle to a stop, leaving engine running. Review test results. If DTC P0420 resets, go to next step. If TEST COMPLETED is displayed on scan tool, and no DTC is set, test is complete.
- If short term fuel trim varied between -20 and +20 percent while test driving vehicle, go to next step. If short term fuel trim was not as specified, check fuel system following procedures in DTC P0171: FUEL SYSTEM LEAN, OR P0172: FUEL SYSTEM RICH .
- Select DATA LIST mode on scan tool. Test drive vehicle under normal driving conditions for 5 minutes. Check HO2S No. 2 output voltage and short term fuel trim. Record readings. Stop vehicle, leaving engine running. Accelerate vehicle to greater than 20 MPH and come to a stop. Repeat process 4 times. Go to next step.
- Increase vehicle speed to 50 MPH in 3rd gear. Release accelerator and allow vehicle to coast for 10 seconds or more. Stop vehicle and let idle for 2 minutes. Test is complete. Turn ignition off. If output voltage of HO2S No. 2 varied from less than 0.3 volt to greater than 0.6 volt during test, replace TWC. If output voltage of HO2S No. 2 did not vary from less than 0.3 volt to greater than 0.6 volt during test, check for open or short between HO2S No. 2 and PCM (Blue and Pink wires on Esteem, or Yellow and Light Green/Black wires on Swift). Repair as necessary. If wires are okay, replace HO2S No. 2.