Symptom:
P0420-CATALYTIC 1/1 EFFICIENCY
When Monitored and Set Condition:
P0420-CATALYTIC 1/1 EFFICIENCY
When Monitored: Engine Run timegreater than 90 seconds. Engine Coolant greater than
70°C (158°F) Vehicle speed greater than 20 MPH and less than 55 MPH. Engine Speed
greater than 1216 RPM and less than 1952 RPM.
Set Condition: As catalyst efficiency deteriorates, the switch rate of the downstream O2
sensor approaches that of the upstream O2 sensor. If at any point during the test the
switch ratio reaches a predetermined value a counter is incremented by one. One Trip
Fault.
POSSIBLE CAUSES
GOOD TRIP EQUAL TO ZERO
VISUALLY INSPECT CATALYTIC CONVERTER
EXHAUST LEAK
ENGINE MECHANICAL CONDITION
AGING O2 SENSOR
CATALYTIC CONVERTER
TEST ACTION APPLICABILITY
1 NOTE:Anew rear O2 Sensor along with an aging front O2 Sensor may cause
the DTC to set. Review the repair history of the vehicle before continuing.
NOTE: If an O2 Sensor or Fuel System Lean DTC(s) is set along with the
Catalytic Converter Efficiency DTC, diagnose the O2 Sensor DTC(s) before
continuing.
NOTE: Check for contaminates that may have damaged the O2 Sensor and
Catalytic Converter: contaminated fuel, unapproved silicone, oil and cool-
ant, repair necessary.
Ignition on, engine not running.
With the DRBIIIt, read DTCs and record the related Freeze Frame data.
Is the Good Trip Counter displayed and equal to zero?
All
Yes → Go To 2
No → Refer to the INTERMITTENT CONDITION symptom in the
Driveability category.
Perform POWERTRAIN VERIFICATION TEST VER-5-NGC.
159
DRIVEABILITY - NGC
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