P0420
DTC P0420: Catalyst System Efficiency Below Threshold (Bank-1)System and Wiring Diagram
System And Wiring Diagram:
System Description
ECM monitors oxygen concentration in the exhaust gas which has passed the warm up three way catalytic converter by HO2S. When the catalyst is functioning properly, the variation cycle of HO2S output voltage (oxygen concentration) is slower than that of A/F sensor output signal because the amount of oxygen in the exhaust gas is stored in warm up three way catalytic converter.
A/F Sensor Description
A/F sensor (1), in place of the conventional HO2S-1, is installed in the center of the exhaust manifold joining section and it consists of a zirconia element (2) which causes the output current to vary according to difference in the oxygen concentration and a heater (3) which activates the element.
A/F sensor detects oxygen concentration in exhaust gas (9) (A/F ratio of the air-fuel mixture) linearly, ranging from LEAN to RICH.
Operation
ECM (5) controls the sensor heater (3) and keeps the sensor element temperature at the specified level (about 750 °C) constantly so that the A/F sensor is activated in the specified way for accurate A/F detection. When the sensor element reaches the specified temperature (it is activated), its impedance drops to the specified value (approx. 30 ohms) by its characteristic. When a certain voltage (about 0.4 V) is applied between sensor elements in this state, circuit current corresponding to the sensor element impedance flows in the sensor circuit. ECM detects this circuit current and judges whether the sensor is in the active state or not. At this time, sensor current is output linearly in the range of +0.01 mA to +some mA on the lean side and -0.01 mA to -some mA on the rich side. The variation in these ranges depends on the difference from the stoichiometry A/F ratio, that is, the amount of oxygen between the atmosphere side and exhaust manifold (7).
According to this sensor output, ECM executes A/F feedback (fuel trim) to achieve the target A/ ratio.
DTC Detecting Condition and Trouble Area
DTC Detecting Condition And Trouble Area:
DTC Confirmation Procedure
WARNING:
^ When performing a road test, select a place where there is no traffic or possibility of a traffic accident and very careful during testing to avoid occurrence of an accident.
^ Road test should be carried out with 2 persons, a driver and a tester, on a level road.
NOTE: Check to make sure that the following conditions are satisfied when using this "DTC Confirmation Procedure".
EVAP leak check model:
^ The following DTCs are not detected: DTCs related to A/F sensor and HO2S
Non-EVAP-leak-check model:
^ Intake air temperature at engine start: -10 °C (14 °F) to 80 °C (176 °F)
^ Intake air temperature: -10 °C (14 °F) to 70 °C (158 °F)
^ Altitude (barometric pressure): 2400 m, 8000 ft or less (560 mmHg, 75 kPa or more)
^ The following DTCs are not detected: DTCs related to ECT sensor, IAT sensor, MAF sensor, barometric pressure sensor and VSS
1. Connect scan tool to DLC with ignition switch turned OFF.
2. Turn ON ignition switch and clear DTC using scan tool.
3. Start engine and warm up to normal operating temperature.
4. Increase vehicle speed to 50 - 60 mph (80 - 100 km/h).
5. Keep above vehicle speed for 10 min. or more.
6. Stop vehicle.
7. Check whether catalyst readiness/monitoring test has completed or not by using scan tool.
If catalyst readiness/monitoring test has not completed, check vehicle conditions (environmental) and repeat Steps 4) through 6).
8. Check DTC and pending DTC.
DTC Troubleshooting
