DTC P0420 - TWC SYSTEM LOW EFFICIENCY BANK 1 GMC Envoy I

Note. For circuit reference, see WIRING DIAGRAMS - 4.3L article.

Circuit Description

Three-Way Catalyst (TWC) system is used to control emission. VCM uses signal from Heated Oxygen Sensor (HO2S) behind TWC read efficiency of TWC. VCM will set DTC P0420 if TWC oxygen storage capacity is less than a predetermined threshold.

Conditions for setting DTC

1. No CMP, ECT, EGR, EVAP, HO2S, IAT, MAF, MAP, TP or VSS DTCs set.
2. No fuel trim, misfire or transmission DTCs set.
3. Engine speed is 900 RPM or more for more than 35 seconds since last idle period.
4. Engine has been running for at least 346 seconds and the long term fuel trim is stable.
5. Predicted catalyst temperature is at least 887°F (475°C).
6. System is in closed loop.
7. BARO is 73 kPa or more.
8. IAT is between 20°F-167°F (-7°C-117°C).
9. ECT is between 167°F- 243°F (75°C-117°C).
10. Engine has been idling for less than 60 seconds.
11. Actual engine speed is within 100 RPM of the desired idle speed.