P0420

DTC P0420 Catalyst System Efficiency Below Threshold (Bank1)

MONITOR DESCRIPTION

DTC Detection Condition:

Monitor Strategy:

Typical Enabling Conditions:

Typical Malfunction Thresholds:

Monitor Result (Mode 06 Data):

The ECM uses Heated Oxygen Sensors (HO2S) mounted in front of and behind the Three-Way Catalytic Converter (TWC) to monitor its efficiency. The front sensor sends pre-catalyst air-fuel information to the ECM. The rear sensor sends post-catalyst information to the ECM. The ECM compares these two signals to determine the efficiency of the TWC and the TWC's ability to store oxygen. During normal operation, the TWC stores and releases oxygen as needed. The capacity to store oxygen results in a low variation in the post-TWC exhaust stream as shown.

If the TWC is functioning normally, the waveform of the heated oxygen sensor (sensor 2) slowly alternates between RICH and LEAN. If the TWC is deteriorated, the waveform alternates frequently between RICH and LEAN. As the catalyst efficiency degrades, its ability to store oxygen is reduced and the TWC output becomes more variable.

When the TWC monitor is activated, the ECM begins to measure the signal length of the sensor 1 and sensor 2. The ECM calculates the signal length rates of the sensor 1 and sensor 2 (catalyst deterioration level). If the catalyst deterioration level exceeds the threshold, the ECM interprets this as a malfunction of the TWC. The ECM illuminates the MIL (2 trip detection logic) and sets the DTC.

The monitor runs after:
- The engine is warmed up (engine coolant temperature is 75 °C (167 °F) or more).
- The vehicle has driven at approximately 60 to 100 km/h (37 to 63 mph) for 15 minutes.

CONFIRMATION ENGINE RACING PATTERN

Confirmation Engine Racing Pattern:

a. Connect the hand-held tester to the DLC3, or connect the probes of the oscilloscope between terminals OXL1, OXL2 and E2 of the ECM connector.
b. Start engine and warm it up with all accessories switched OFF until the engine coolant temperature becomes stable.
c. Run the engine at between 2,500 rpm and 3,000 rpm for about 3 minutes.
d. After confirming that the waveform of the bank 1 sensor 1 (OXL1) which oscillates between 0 V and 1 V under feedback to the ECM, check the waveform of the bank 1 sensor 2 (OXL1).






HINT: If there is a malfunction in the system, the waveform of sensor 2 (OXL2) may become similar to that of sensor 1 (OXL1) shown in the diagram.

INSPECTION PROCEDURE

HINT: Read freeze frame data using the hand-held tester or the 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 (Continued):

Step 2 (Continued) - 3:

Hand-held tester:

Step 1 - 3:

Step 4:

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