P0420

DTC P0420 Catalyst System Efficiency Below Threshold (Bank 1)

MONITOR DESCRIPTION

DTC Detection Condition:

Monitor Strategy:

Typical Enabling Conditions (Part 1):

Typical Enabling Conditions (Part 2):

Typical Malfunction Thresholds:

The ECM uses the 2 Heated Oxygen (HO2) sensors, mounted in front of and behind the Three-Way Catalytic Converter (TWC), to monitor its efficiency.

The first sensor, Sensor 1, sends pre-catalyst information to the ECM. The second sensor, Sensor 2, sends post-catalyst information to the ECM. The ECM compares the information transmitted by these 2 sensors to determine the efficiency of the TWC performance and its ability to store oxygen.

When the TWC is functioning properly, the variation in the oxygen concentration in the exhaust gas, after it has passed through the TWC, is small. In this condition, the voltage output of sensor 2 slowly alternates between the rich and lean signal voltages (shown in the illustration below). As the TWC performance efficiency deteriorates, its oxygen storage capacity decreases, and the variation in the oxygen concentration in the exhaust gas increases. As a result, the sensor voltage output fluctuates frequently. While the catalyst monitor is running, the ECM measures the signal lengths of both sensors 1 and 2, and calculates the ratio of the signal lengths to determine the extent of the TWC deterioration. If the deterioration level exceeds the preset threshold, the ECM interprets this as the TWC malfunction. The ECM then illuminates the MIL and sets the DTC.

This monitor begins to run when the following preconditions apply:
- The engine has warmed up (the engine coolant temperature is 75 degrees C [167 degrees F] or more).
- The vehicle has driven at between 60 km/h and 100 km/h (37 mph and 63 mph) for 15 minutes.

MONITOR RESULT

Refer to detailed information Mode 6 Data

CONFIRMATION DRIVING PATTERN




1. If using the intelligent tester: Connect the intelligent tester to the DLC3.
2. If not using the intelligent tester: Connect oscilloscope tester probes to terminals OX1A (front Heated Oxygen [HO2] sensor: Sensor 1), OX1B (rear HO2 sensor: Sensor 2) and E1 of the ECM connector.
3. Start the engine.
4. Warm up the engine with all the accessories switched OFF until the engine coolant temperature stabilizes.
5. Run the engine at an engine speed between 2,500 rpm and 3,000 rpm for approximately 3 minutes.




6. Check that the waveform of the OX1A (rear HO2 sensor) signal.

HINT: If there is still a malfunction in the system, the waveform of OX1B may become similar to the OX1A waveform shown in the diagram above.

Step 1-2:

Step 2(Continued):

Step 2(Continued)-4:

INSPECTION PROCEDURE

HINT: Read freeze frame data using the intelligent tester. Freeze frame data records the engine conditions when malfunctions are detected. When troubleshooting, freeze frame data can help determine if the vehicle was moving or stationary, if the engine was warmed up or not, if the air-fuel ratio was lean or rich, and other data from the time the malfunction occurred.