LEMON Manuals: Even more car manuals for everyone
Home >> Ford >> 2000 >> Contour SE, 2.5 L, Standard >> Repair and Diagnosis >> External Pages >> Different car >> Section 1975 (Engine Controls - Powertrain DTC Charts And Descriptions - (Hybrid)) >> DTC Diagnosis >> P0420 - Catalyst System Efficiency Below Threshold (Bank 1)

P0420 - Catalyst System Efficiency Below Threshold (Bank 1)

WARNING: This page is about a different car, the 2007 Mercury Mariner and 2007 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 catalyst system efficiency is below the acceptable threshold.
Possible Causes: 
  • Use of leaded fuel
  • Damaged heated oxygen sensor (HO2S)
  • Out of range 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   - - refer to PINPOINT TEST HF .
scientia non olet · About LEMON Manuals