Troubleshooting
DTC P0420 CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD (BANK 1)CIRCUIT DESCRIPTION
DTC Detection Condition:
The ECM compares the two waveforms of the heated oxygen sensors located before and after the catalyst to determine whether or not the catalyst performance has deteriorated.
Air-fuel ratio feedback compensation keeps the waveform of the heated oxygen sensor in front of the catalyst alternates between back and forth, from RICH to LEAN.
If the catalyst is functioning normally, the waveform of the heated oxygen sensor behind the catalyst switches back and forth between RICH and LEAN much more slowly than the waveform of the heated oxygen sensor in front of the catalyst.
When both waveforms change at a similar rate, it indicates that the catalyst performance has deteriorated.
MONITOR DESCRIPTION
Monitor Strategy:
Typical Enabling Conditions:
Typical Malfunction Thresholds:
Component Operating Range:
Monitor Result (MODE 06 DATA):
The vehicle is equipped with the two heated oxygen sensors (O2S). One is mounted upstream from the three-way catalytic (TWC) converter (front heated oxygen sensor "sensor 1"), the second is mounted downstream (heated oxygen sensor "sensor 2"). The catalyst efficiency monitor compares the sensor 1 and 2 signals in order to calculate TWC ability to store oxygen.
During normal operation, the TWC stores and releases oxygen as needed. This results in low oxygen variations in the post TWC exhaust stream as shown.
As the TWC's efficiency degrades, its ability to store oxygen is reduced. This causes higher variations in post TWC exhaust stream oxygen content and results in increased sensor 2 signal activity as shown.
When running the monitor, the ECM compares sensor 1 and sensor 2 signals over a specific time to determine the TWC efficiency. The ECM begins by calculating the signal length for both sensors.
CONFIRMATION DRIVING PATTERN
Confirmation Driving Pattern:
a. Connect the hand-held tester to the DLC3, or connect the tester probes of the oscilloscope between terminals OX1A, OX1B and E1 of the ECM connector.
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. After confirming that the waveform of the bank 1 sensor 1 (OX1A) which oscillates between 0 V and 1 V under a feedback to the ECM, check the waveform of the bank 1 sensor 2 (OX2A).
HINT: If there is malfunction in the system, the waveform of "sensor 2" (OX2A) may become a similar to the one of "sensor 1" (OX1A) as shown in the diagram.
Step 1 - 4:
INSPECTION PROCEDURE
HINT: Read freeze frame data using the hand-held tester or the OBD II scan tool. Freeze frame data records the engine conditions when a malfunction is detected. When troubleshooting, it is useful for determining whether the vehicle was running or stopped, the engine was warmed up or not, the air-fuel ratio was lean or rich, etc. at the time of the malfunction.
HINT:
Hand-held tester only:
- The following procedure enables the technician to identify a trouble area if malfunction in both front and rear heated oxygen sensors is other than the catalyst converter, or the malfunction that indicates the actual air-fuel ratio extremely RICH or LEAN.
- Narrowing down the trouble area is possible by performing "A/F CONTROL" ACTIVE TEST (heated oxygen sensor or other trouble areas can be distinguished).
"A/F CONTROL" is ACTIVE TEST which changes the injection volume -12.5 % or +25 %.
1. Connect the hand-held tester to the DLC3 on the vehicle.
2. Turn the ignition switch ON.
3. Warm up the engine by running the engine at 2,500 rpm for approximately 90 seconds.
4. Select the item "DIAGNOSIS/ENHANCED OBD II/ACTIVE TEST/A/F CONTROL."
5. Perform A/F CONTROL with the engine in an idle condition (press the right or left button).
Result:
Heated oxygen sensor reacts in accordance with increase and decrease of injection volume
+25 % ->rich output: More than 0.5 V
-12.5 % ->lean output: Less than 0.4 V
NOTE: There is a delay of few seconds in the sensor 1 (front sensor) output, and there is about 20 seconds delay at maximum in the sensor 2 (rear sensor)
The following of the A/F CONTROL procedure enables the technician to check and graph the voltage outputs of both the heated oxygen sensors.
For displaying the graph indication, enter "ACTIVE TEST/A/F CONTROL/USER DATA," then select "O2S B1S1 and O2S B1S2" by pressing "YES" button and push "ENTER" button before pressing "F4" button.