Re: dtc p0420
Diagnostic Trouble Codes (DTC) P0420 and P0421 indicate that bank 1 catalyst system efficiency is below the acceptable threshold.
NOTE 1: Complete the spark timing check in Quick Test before proceeding with this test step. Spark timing retarded below specification can increase exhaust gas temperature and decrease catalyst efficiency over time.
NOTE 2: Be sure customer has not:
Refueled vehicle with leaded gasoline.
Noticed high vehicle oil consumption.
NOTE 3: If entering this Pinpoint Test for symptoms only, go immediately to HF5 .
NOTE 4: Internal deterioration of a catalytic converter is usually caused by abnormal engine operation upstream of the catalyst. Events that can produce higher than normal temperatures in the catalyst are particularly suspect. For example, misfiring can cause higher than normal catalyst operating temperatures.
Use of leaded fuel.
Damaged ECT sensor.
Downstream HO2S wires improperly connected.
Fuel pressure too high.
Damaged exhaust system pipe.
Damaged exhaust manifold.
Damaged muffler/tailpipe assembly.
Damaged catalytic converter.