Note. Use illustration for circuit reference. (Схема №6)
Circuit Description
Three-Way Catalyst (TWC) system is used to control emissions. PCM uses signals from Heated Oxygen Sensors (HO2S) to read efficiency of TWC. PCM will set DTC P0420 if TWC oxygen storage capacity is less than a predetermined threshold.
Conditions required to set DTC are
- No related DTCs set.
- Engine is operating in closed loop.
- Engine coolant temperature is greater than 158°F (70°C) and less than 248°F (120°C).
- Calculated airflow is 2.5-7 grams per second.
- Vehicle speed is less than 3 MPH.
- Catalyst temperature is greater than 842°F (450°C) and less than 1742°F (850°C).
- Airflow reset time is equal to or greater than 8 seconds.
- Airflow to reset is equal to 9 grams per second.
- Absolute pressure is more than 72 kPa.
- Intake air temperature is more than 14°F (-10°C) and less than 158°F (70°C).
- Engine run time is more than 360 seconds.
- TP sensor is at less than 3 percent.
- Idle time is less than 60 seconds.
- Oxygen capacity time is less than or equal to 1.5 seconds.
Diagnostic Aids
Check for poor connection at PCM. Inspect harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal connection. Observe scan tool while moving all related harnesses and connectors. A change in scan tool display indicates fault location.
Ensure engine has reached operating temperature. Place gear selector in Park. Using scan tool, monitor HO2S-1 and HO2S-2 values while using scan tool IAC RPM control function to maintain MAF at 10 grams per second. Compare activity between HO2S-1 and HO2S-2 for 30 seconds. If activity between both HO2S is about equal, a problem exists. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.