DTC P0420: Catalyst System Efficiency Below Threshold (Bank 1)

P0420 - CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD (BANK 1)

Description: This DTC sets when the bank 1 catalyst system efficiency is below the acceptable threshold.
Possible Causes: Use of leaded fuel Damaged heated oxygen sensor (HO2S) Out of range engine coolant temperature (ECT) sensor High fuel pressure Damaged exhaust manifold Damaged catalytic converter Oil contamination Cylinder misfiring Downstream HO2S wires incorrectly connected Damaged exhaust system pipe Damaged muffler/tailpipe assembly Retarded spark timing Leaking fuel injector
Diagnostic Aids: Under normal closed loop fuel conditions, high efficiency catalysts have oxygen storage which reduces the frequency and amplitude of the downstream HO2S as compared with an upstream HO2S signal. As catalyst efficiency deteriorates, its ability to store oxygen declines and the downstream HO2S signal has an increased amplitude and frequency, approaching the amplitude and frequency of the upstream HO2S. For vehicles with universal HO2S, the PCM compares the signal line length of the downstream HO2S to an expected signal line length of the downstream HO2S with a deteriorated catalytic converter. For all others, the signal line lengths of the downstream HO2S are compared against the signal line lengths of the upstream HO2S.
Application	Key On Engine Off	Key On Engine Running	Continuous Memory
All	GO to PINPOINT TEST HF .