P0420

DTC P0420 CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD (BANK 1)

MONITOR DESCRIPTION

DTC Detection Conditions:

Monitor Strategy:

Typical Enabling Conditions:

Typical Malfunction Thresholds:

The ECM uses the two 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 two 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). 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°C [167°F] or more)
- The vehicle has driven at between 37 mph and 63 mph (60 km/h and 100 km/h) for 15 minutes.

Monitor Result:

- TWC denotes Three-Way Catalytic Converter.
- Sensor 1 denotes the front Heated Oxygen (HO2) sensor, in front of the TWC. Sensor 2 denotes the rear HO2 sensor, behind the TWC.
- Refer for detailed information on Checking Monitor Status.

CONFIRMATION DRIVING PATTERN




a. If using a hand-held tester: Connect the hand-held tester to the DLC3.
b. If not using a hand-held tester: Connect oscilloscope tester probes to terminals OXL1 (front Heated Oxygen [HO2] sensor: Sensor 1), OXL2 (rear HO2 sensor: Sensor 2) and E1 of the ECM connector.
c. Start the engine.
d. Warm up the engine with all the accessories switched OFF until the engine coolant temperature stabilizes.
e. Run the engine at an engine speed of between 2,500 rpm and 3,000 rpm for approximately 3 minutes.
f. Check that the waveform of the OXL2 (rear HO2 sensor) signal.






HINT: If there is still a malfunction in the system, the waveform of OX1B may become similar to the OXL1 waveform shown in the diagram on the left.

INSPECTION PROCEDURE

HINT: Read freeze frame data using a hand-held tester or OBD II scan tool. Freeze frame data record the engine condition 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.

Step 1 - 2:

Step 2 (Contd.) - 3:

Hand-held tester

Step 1 - 4:

OBD II scan tool (excluding the hand-held tester)