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Home >> Ford >> 2000 >> Contour SE, 2.0 3, Standard >> Repair and Diagnosis >> External Pages >> Different car >> Section 1341 (Engine Controls - Powertrain DTC Charts & Descriptions - (Hybrid)) >> DTC Diagnosis >> DTC P0420: Catalyst System Efficiency Below Threshold (Bank 1)

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

WARNING: This page is about a different car, the 2006 Mercury Mariner and 2006 Ford Escape. However, it is still accessible from the selected car via links, so may be relevant.
P0420 - CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD (BANK 1)

Description:  Indicates the bank 1 catalyst system efficiency is below the acceptable threshold.
Possible Causes: 
  • Use of leaded fuel.
  • Damaged heated oxygen sensor (HO2S).
  • Malfunctioning cylinder head temperature (CHT) sensor.
  • High fuel pressure.
  • Damaged exhaust manifold.
  • Damaged catalytic converter.
  • Oil contamination.
  • Cylinder misfiring.
  • Damaged exhaust system pipe.
  • Damaged muffler/tailpipe assembly.
Diagnostic Aids:  Compare the HO2S11 and HO2S12 switch rate and amplitude. Under normal closed loop fuel conditions, high efficiency catalysts have oxygen storage which makes the switching frequency of the HO2S12 very slow and reduces the amplitude of those switches as compared to the HO2S11. As catalyst efficiency deteriorates, its ability to store oxygen declines and the HO2S12 signal begins to switch more rapidly with the increase in amplitude, approaching the switching rate and amplitude of the HO2S11. Once beyond an acceptable limit the DTC is set.
Application  Key On Engine Off  Key On Engine Running  Continuous Memory 
All - - GO to Pinpoint Test HF .
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