1A
DTC P0420: Catalyst System Efficiency below Threshold
System and Wiring Diagram
1. HO2S-1 3. Warm up three way catalytic converter 5. ECM
2. HO2S-2 4. Three way catalytic converter 6. Other sensors
Circuit Description
ECM monitors oxygen concentration in the exhaust gas which has passed the warm up three way catalytic converter and three way catalytic converter by HO2S-2. When the catalyst is functioning properly, the variation cycle of HO2S-2 output voltage (oxygen concentration) is slower than that of HO2S-1 output voltage because of the amount of oxygen in the exhaust gas which has been stored in warm up three way catalytic converter and three way catalytic converter.
Reference
[A]: Oscilloscope waveforms
DTC Detecting Condition and Trouble Area
DTC detecting condition Trouble area
• While vehicle running at constant speed under other than high load.
• Time from rich or lean switching command is output till HO2S-2 output voltage crosses 0.45 V is less than specified value.
(*2 driving cycle detection logic, monitoring once/1 driving)
• Exhaust gas leak
• Warm up three way catalytic converter malfunction
• HO2S-2 malfunction
• HO2S-1 malfunction
• Three way catalytic converter malfunction
DTC Confirmation Procedure
WARNING:
• When performing a road test, select a place where there is no traffic or possibility of a traffic accident and be 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”.
• Intake air temp.: –7 °C, 19.4 °F or higher
• Engine coolant temp.: 70 °C, 158 °F or higher
• Altitude (barometric pressure): 2500 m, 8200 ft or less (540 mmHg, 72 kPa or more)
1) Connect scan tool to DLC with ignition switch turned OFF.
2) Turn ON ignition switch and clear DTC using scan tool.
3) Increase vehicle speed to 50 – 60 mph, 80 – 100 km/h. (engine speed: 2500 – 3000 r/min.)
4) Keep above vehicle speed for 10 min. or more (Throttle valve opening is kept constant in this step).
5) Stop vehicle and check if DTC/pending DTC exists using scan tool. If not, check if catalyst monitoring test has completed using scan tool. If not in both of above checks (i.e., no DTC/pending DTC and catalyst monitoring test not completed), check vehicle condition (environmental) and repeat Step 3) through 5).
DTC Troubleshooting
Step Action YES NO
1
Was “Engine and Emission Control System Check” performed?
Go to Step 2.
Go to Engine and Emission Control System Check:M13A with VVT .
2
Exhaust system visual check
1) Check exhaust system for leaks, damage and loose connection.
Is it in good condition?
Go to Step 3.
Repair or replace.
3
HO2S-2 ground check
1) Disconnect connector from HO2S-2 with ignition switch turned OFF.
2) Check for proper connection to HO2S-2 connector at “WHT” and “BLK/BLU” wire terminals.
3) If wire and connection are OK, measure resistance between “BLK/BLU” wire terminal of HO2S-2 connector and engine ground.
Is resistance less than 5 Ω?
Go to Step 4.
“BLK/BLU” wire open or high resistance circuit. Poor “E118-35” terminal connection.
Faulty ECM ground. If they are OK, substitute a known-good ECM and recheck.
4
ECM voltage check
1) Turn ON ignition switch.
2) Measure voltage between “E119-33” terminal of ECM connector and vehicle body ground.
Is voltage 4 – 5 V?
Go to Step 5.
Poor “E119-33” terminal connection. If connection is OK, substitute a known-good ECM and recheck.
5
Wire circuit check
1) Disconnect connectors from ECM with ignition switch turned OFF.
2) Measure resistance between “WHT” wire terminal of HO2S-2 connector and “E119-33” terminal of ECM connector.
Is resistance less than 5 Ω?
Go to Step 6.
“WHT” wire high resistance circuit or open circuit.
6
Wire circuit check
1) Measure resistance between “WHT” wire terminal of HO2S-2 connector and body ground.
Is resistance infinity?
Go to Step 7.
“WHT” wire shorted to ground circuit.
7
HO2S-2 signal circuit check
1) Turn ON ignition switch.
2) Measure voltage between “WHT” wire terminal of HO2S-2 connector and vehicle body ground.
Is voltage 0 V?
Replace exhaust manifold (built in warm up three way catalytic converter) and exhaust pipe (built in three way catalytic converter).
“WHT” wire shorted to other circuit. If wire is OK, replace HO2S-2.
NOTE:
Upon completion of inspection and repair work, perform “DTC Confirmation Procedure” and confirm that the trouble has been corrected.