P0420
3UZ-FE ENGINE CONTROL SYSTEM: SFI SYSTEM: P0420: Catalyst System Efficiency Below Threshold (Bank 1)
DTC P0420 - Catalyst System Efficiency Below Threshold (Bank 1)
DTC P0430 - Catalyst System Efficiency Below Threshold (Bank 2)
MONITOR DESCRIPTION
The ECM uses the heated oxygen sensors 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 2 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 below.
If the catalyst is functioning normally, the waveform of the heated oxygen sensor (sensor 2) 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 heated oxygen sensor (sensor 1) and heated oxygen sensor (sensor 2). The ECM calculates the rate of the signal length of the heated oxygen sensor (sensor 1) and heated oxygen sensor (sensor 2) (catalyst deterioration level). If the catalyst deterioration level exceeds the threshold, the ECM interprets this as a catalyst malfunction. The ECM illuminates the MIL (2 trip detection logic) and sets a DTC.
The monitor runs after:
- The engine is warmed up (Engine Coolant Temperature (ECT) is 75°C (167°F) or more).
- The vehicle is driven at approximately 60 to 100 km/h (37 to 63 mph) for 15 minutes.
MONITOR STRATEGY
TYPICAL ENABLING CONDITIONS
TYPICAL MALFUNCTION THRESHOLDS
MONITOR RESULT
Refer to CHECKING MONITOR STATUS Mode 6 Data.
CONFIRMATION DRIVING PATTERN
- (a) Connect the Techstream to the DLC3.
- (b) Enter the following menus: Powertrain / Engine and ECT / Data List / O2S B1 S1 or O2S B2 S1.
- (c) Start the engine and warm it up with all the accessories switched OFF until the ECT becomes stable.
- (d) Run the engine at 2500 to 3000 rpm for about 3 minutes.
HINT: Control the engine RPM so that the calculated catalyst temperature can be between 550 and 800°C (1022 and 1472°F). The calculated catalyst temperatures of bank 1 and bank 2 can be read by viewing Catalyst Temp (B1 S1) and Catalyst Temp (B2 S1) of the Data List.
- (e) Confirm that heated oxygen sensor (bank 1 sensor 1 (OX1A) and bank 2 sensor 1 (OX2A)) have waveforms that are around 0.5 V during feedback to the ECM. Then check the waveform of the heated oxygen sensor (bank 1 sensor 2 (OX1B) and bank 2 sensor 2 (OX2B)) for the same waveforms (0.5 V during feedback).
HINT: If there is a malfunction in the catalyst, the waveform of the heated oxygen sensor (sensor 2) (OX1B, OX2B) is almost the same as that of the heated oxygen sensor (sensor 1) (OX1A, OX2A), which is shown.
WIRING DIAGRAM
INSPECTION PROCEDURE
HINT:
- Read freeze frame data using the Techstream. 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.
- If DTC P0420 is displayed, check the bank 1 catalyst.
- If DTC P0430 is displayed, check the bank 2 catalyst.
- Bank 1 includes No. 1 cylinder, but bank 2 does not. The No. 1 cylinder is located in the front part of the engine, opposite the transmission.
PROCEDURE
1. CHECK OTHER DTC OUTPUT (IN ADDITION TO DTC P0420, P0430)
(a) Connect the Techstream to the DLC3.
(b) Turn the ignition switch ON and turn the tester ON.
(c) Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.
(d) Read the DTCs.
Result:
B -- GO TO RELEVANT DTC CHART
A -- Continue to next step.
2. CHECK FOR EXHAUST GAS LEAKAGE
NG -- REPAIR OR REPLACE EXHAUST GAS LEAKAGE POINT
OK -- Continue to next step.
3. INSPECT HEATED OXYGEN SENSOR (RESISTANCE)
(a) Disconnect the H9, H10, H15 and H16 sensor connectors.
(b) Measure the resistance of the sensor.
Standard resistance (bank 1 sensor 1):
Standard resistance (bank 2 sensor 1):
Standard resistance (bank 1 sensor 2):
Standard resistance (bank 2 sensor 2):
NG -- REPLACE HEATED OXYGEN SENSOR
OK -- Continue to next step.
4. PERFORM ACTIVE TEST USING TECHSTREAM (A/F CONTROL)
HINT: It is possible that the malfunctioning area can be found using the Active Test Control the Injection Volume for A/F sensor operation. The Active Test can determine if the heated oxygen sensor or other potential trouble areas are malfunctioning or not.
The injection volume can be switched to -12.5% (decrease) or +25% (increase) by the Active Test.
The Active Test procedure enables a technician to check and graph the output voltage of the heated oxygen sensors.
- Procedure:
1 Connect the Techstream to the DLC3.
2 Turn the ignition switch ON.
3 Warm up the engine by running the engine at 2500 rpm for approximately 90 seconds.
4 Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F sensor.
5 Perform the Active Test while the engine is idling.
Standard:
Heated oxygen sensor reacts in accordance with the increase and decrease of injection volume:
+25% -> Rich output: More than 0.55 V
-12.5% -> Lean output: Less than 0.4 V
NOTE:
The heated oxygen sensor (sensor 1) output has a few seconds of delay and the heated oxygen sensor (sensor 2) output has a maximum of 20 seconds of delay.
If the vehicle is short on fuel, the air-fuel ratio becomes lean and the DTCs will be recorded.
NG -- REPLACE HEATED OXYGEN SENSOR
OK -- Continue to next step.
5. CHECK DTC OUTPUT (DTC P0420 AND/OR P0430)
(a) According to the output DTCs in the step 1 (CHECK ANY OTHER DTCS OUTPUT), proceed to next step referring to the table below.
Result
B -- REPLACE CATALYST CONVERTER (for Bank 2)
A -- REPLACE CATALYST CONVERTER (for Bank 1)
6. REPLACE CATALYST CONVERTER (for Bank 1)
(a) Replace the catalyst converter (for Bank 1) Removal.
NEXT -- REPLACE EXHAUST FRONT PIPE
7. REPLACE CATALYST CONVERTER (for Bank 2)
(a) Replace the catalyst converter (for Bank 2) Removal.
NEXT -- REPLACE EXHAUST FRONT PIPE