Catalyst Monitor

OBD System Description - Catalyst Monitor

CatalystBank1

DTC Description / Detecting Condition / Confirmation Procedure
P0420 refer to [DTC P0420: Catalyst System Low Efficiency]. P0420

Monitor Strategy Description
Detects reduced Catalyst conversion efficiency, through correlation of Oxygen Storage. A/F shifts are commanded at idle, and Oxygen Sensors are monitored to determine the amount of Oxygen Storage (in units of time), which is EWMA filtered.

Malfunction Criteria
EWMA Oxygen Storage Time for Bank 1 (to report FAIL) <= 2.25 s (when passing)
To Pass this Monitor After a Failure is Detected, the Following Must be Met:
EWMA Oxygen Storage Time for Bank 1 (to report PASS) >= 2.75 s (when failing) - allows hysteresis to prevent excessive MIL cycling

Enable Conditions
(Intrusive Test Starts when These Conditions are Met)
Engine Runtime >= 570 s
AND (Purge Concentration Learned = TRUE
OR Low Purge Fuel Concentration
((Purge Concentration Lower than Threshold) < 2.0996%
AND (Low Concentration Timer Longer than Threshold)) > 45 s
AND Airflow within range: <= 8.5 g/s (For AT)
AND Airflow within range: <= 7.5 g/s (For MT)
>= 2.25 g/s
AND Throttle closed <= 1.5015%
AND Coolant Temp within range >= 70 °C
<= 109 °C
AND Ambient Temp within range >= -7 °C
<= 105 °C
AND Barometric Pressure above minimum >= 72 kPa
AND Number of Test Attempts Not Excessive <= 12
AND Closed Loop Fuel Control Active = TRUE
AND Injectors Turned Off for Engine Protection = FALSE
AND Catalyst Temp within range <= 975 °C
>= 312.5 °C (For AT)
>= 300 °C (For MT)
AND Fuel Integrator deviation <= 0.03
AND Vehicle speed <= 1.86 mph
AND (A/T PN Transitions Not Allowed = FALSE
AND (Auto Trans not in P/N)) = TRUE
OR (A/T PN Transitions Allowed = FALSE
AND (P/N transitions period below max. allowed)) <= 1.5
AND (BLM18 Learned (Gear in Drive) = TRUE
OR (BLM20 Learned (Gear in Park/Neutral) = TRUE
AND (Sufficient Driving Airflow (since last test) >= 11 g/s (For AT)
AND (Sufficient Driving Airflow (since last test) >= 9 g/s (For MT)
present for Sufficient Time to Prep Catalyst) >= 12 s
AND End of Diagnostic Airfuel Ramping = FALSE
AND idling time <= 75 s
AND Test not complete (Sampling Allowed) = FALSE
AND No disabling faults present (Refer to Disabling Faults List - Included with certification documentation) = FALSE
AND No instrumentation slews active = FALSE
AND OFVC device control active = FALSE
AND Accumulated Combusted Fuel >= 5 g
(Conditions to Keep Intrusive Test Running)
Engine Speed Error (Actual to Desired) <= 150 RPM
AND Commanded Air/Fuel Switch Achieved Pre-O2 (Lean) < 1 s
(Switch Defined As) <= 0.3003 mV
AND Commanded Air/Fuel Switch Achieved Pre-O2 (Rich) < 1 s
(Switch Defined As) >= 0.6001 mV
AND Commanded Fan State (On/Off) Not Changed
AND Commanded AC Clutch State Not Changed
AND ((Trans in P/N (When PN Mode Selected)
OR (Trans Shift after Max Time (When PN Not Selected))) <= 1.5 s
where: Park/Neutral Mode Selected = FALSE
AND Evap Diagnostic Not Intrusively Controlling Purge <> CeEVPD_PRG_INACTIVE

Time required
N/A

MODE $06 Data

Catalyst Monitor Bank 1:

Refer to [MODE $06 Diagnostic Description]. Mode 6 Data