Troubleshooting
DTC P0420 Catalyst System Efficiency Below Threshold (Bank 1)MONITOR DESCRIPTION
DTC Detecting Condition:
Monitor Strategy:
Typical Enabling Conditions:
Typical Malfunction Thresholds:
Component Operating Range:
Monitor Result (Mode 06 Data):
The vehicle is equipped with two heated oxygen sensors. One is mounted upstream from the TWC (Three-Way Catalytic) converter (Front Oxygen Sensor, "sensor 1"), the second is mounted downstream (Rear Oxygen Sensor "sensor 2"). The catalyst efficiency monitor compares the sensor 1 and sensor 2 signals in order to calculate TWC ability to store the 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.
CONFIRMATION ENGINE RACING PATTERN
1. Connect the hand-held tester to the DLC3, or connect the probe of the oscilloscope between terminals OX1A, OX1B, OX2A, OX2B and E1 of ECM connector.
2. Start the engine and warm it up with all the accessories switched OFF until engine coolant temperature becomes stable.
3. Race the engine at 2,500 - 3,000 rpm for approximately 3 min.
4. After confirming that the waveform of the heated oxygen sensor (bank 1, 2 sensor 1 (OX1A, OX2A)), oscillate around 0.5 V during feedback to the ECM, check the waveform of the heated oxygen sensor (bank 1, 2 sensor 2 (OX1B, OX2B)).
HINT: If there is a malfunction in the system, the waveform of the heated oxygen sensor (bank 1, 2 sensor 2 (OX1B, OX2B)) is almost the same as that of the heated oxygen sensor (bank 1, 2 sensor 1 (OX1A, OX2A)) on the left. There are some cases where, even though a malfunction exists, the MIL may either light up or not light up.
Step 1 - 3:
Step 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, 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, as well as other data from the time when a malfunction occurred.
HINT:
Hand-held tester only:
Narrowing down the trouble area is possible by performing ACTIVE TEST of the following "A/F CONTROL" (Heated oxygen sensor or another can be distinguished).
a. Perform ACTIVE TEST by hand-held tester (A/F CONTROL).
HINT: "A/F CONTROL" is the ACTIVE TEST which changes the injection volume to -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 with the engine speed at 2,500 rpm for approximately 90 seconds.
4. Select the menu "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 few second delay in the sensor 1 (front sensor) output. And there is approximately 20 seconds delay in the sensor 2 (rear sensor).
The following A/F CONTROL procedure enables the technician to check and graph the voltage output of the heated oxygen sensors (sensor 1 and 2).
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.
NOTE:
If the vehicle is short of fuel, the air-fuel ratio becomes LEAN and DTCs P0133 and/or P0153 will be recorded, and the MIL then comes on.
- If different DTCs related to different systems while terminal E2 as ground terminal are output simultaneously, terminal E2 may be open.
- 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.
- A high heated oxygen sensor (sensor 1) voltage (0.5 V or more) could be caused by a rich air fuel mixture. Check for conditions that would cause the engine to run rich.
- A low heated oxygen sensor (sensor 1) voltage (0.4 V or less) could be caused by a lean air fuel mixture. Check for conditions that would cause the engine to run lean.