Code P0420, Catalyst Efficiency Low (Bank 1)
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"S" & "T" SERIES 4.3L (VIN W)
Check the following:
- Ensure 3-way catalyst is factory original for application. Check converter for dents, severe discoloration, holes, loose internal (rattle) materials, etc.
- Check exhaust for leaks or missing hardware.
- Ensure oxygen sensor is secure and that sensor pigtail is not damaged or touching hot exhaust.
- Check all control module and sensor grounds. Check sensor high and low circuits for intermittent open or short to ground.
If no problems are found, catalytic converter is bad. If converter needs to be replaced, ensure that conditions which may damage new converter do not exist i.e. misfire, high oil or coolant consumption or retarded or weak spark.