Troubleshooting

DTC P0420 CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD (BANK 1)

HINT:
- If DTC P0420 is displayed, check the bank 1 catalyst.
- If DTC P0430 is displayed, check the bank 2 catalyst.
- Bank 1 includes cylinder No. 1, but bank 2 does not. Cylinder No. 1 is located in the front part of the engine, opposite the transmission.

MONITOR DESCRIPTION

DTC Detection Condition:

Monitor Strategy:

Typical Enabling Conditions:

Typical Malfunction Thresholds:

Monitor Result:

The ECM uses heated oxygen sensor (HO2S) mounted before and after the three-way catalyst (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 judge the efficiency of the catalyst and the catalyst'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 catalyst is functioning normally, the waveform of the rear HO2S slowly switches between RICH and LEAN. If the catalyst is deteriorated, the waveform will alternate frequently between RICH and LEAN. As the catalyst efficiency degrades, its ability to store oxygen is reduced and the catalyst output becomes more variable.

When running the catalyst monitor, the ECM begins to measure the signal length of the front HO2S and rear HO2S. The ECM calculates the rate of signal length of the front HO2S and rear HO2S (catalyst deterioration level). If the catalyst deterioration level exceeds the threshold, the ECM interprets this as catalyst deterioration. The ECM illuminates the Malfunction Indicator Light (MIL) (2 trip detection logic) and sets a DTC.

The monitors runs after:
- The engine is warmed up (Engine Coolant Temperature (ECT) is 75 °C (167 °F) or more).
- Acceleration and deceleration are performed at approximately 60 km/h (37 mph) for 15 minutes.

CONFIRMATION DRIVING PATTERN

Confirmation Driving Pattern:

a. Connect the hand-held tester to the DLC3.
b. Start the engine and warm it up with all the accessories switched OFF until the engine coolant temperature becomes stable.
c. Run the engine at 2,500 to 3,000 rpm for about 3 minutes.
d. Confirming that HO2S bank 1 sensor 1 (OXL1) and bank 2 sensor 1 (OXR1) have waveforms that are around 0.5 V during feedback to the ECM. Then check the waveform of HO2S bank 1 sensor 2 (OXL2) and bank 2 sensor 2 (OXR2).

HINT: The system is malfunctioning when the waveforms of HO2S OXL1 and OXR1 are similar to HO2S OXL2 an OXR2.
In some cases, a malfunction exists but the MIL does not illuminate.

Wiring Diagram:

WIRING DIAGRAM

Step 1 - 2:

Step 3:

Step 4:

INSPECTION PROCEDURE

REPLACE CATALYST CONVERTER (BANK 1 OR BANK 2) AND FRONT EXHAUST PIPE

HINT: Read freeze frame data using the hand-held tester. Freeze frame data records the engine conditions when a malfunction is detected. When troubleshooting, freeze frame data can help determine if the vehicle was running or stopped, 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.

NOTE: Replace both the front catalyst and rear catalyst (front exhaust pipe) of the damaged bank.