Troubleshooting
DTC P0420 CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD (BANK 1)CIRCUIT DESCRIPTION
DTC Detection Condition:
The ECM compares the 2 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.
HINT:
- Bank 1 refers to the bank that includes cylinder No.1.
- Bank 2 refers to the bank that does not include cylinder No.1.
- Sensor 1 refers to the sensor closest to the engine assembly.
- Sensor 2 refers to the sensor farthest away from the engine assembly.
MONITOR DESCRIPTION
Monitor Strategy:
Typical Enabling Conditions:
Typical Malfunction Thresholds:
Component Operating Range:
Monitor Result (Mode 06 Data):
The vehicle is equipped with the four heated oxygen sensors (O2S). Two of them are mounted upstream from the three-way catalytic (TWC) converter (front heated oxygen sensor "sensor 1"), the rest are mounted downstream (rear 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.
CONFIRMATION ENGINE RACING PATTERN
HINT: Follow this procedure to active and condition the heated oxygen sensors prior to observation of their respective waveform output.
Confirmation Engine Rancing Pattern:
a. Connect the hand-held tester to the DLC3, or connect the oscilloscope probe between terminals OX1A (bank 1, sensor 1), OX2A (bank 1, sensor 2), OX1B (bank 2, sensor 1), OX2B (bank 2, sensor 2) and E2 of the ECM connectors.
b. Start the engine and warm it up with all accessories switched OFF until the engine coolant temperature become stable.
c. Run the engine at 2,500 to 3,000 rpm for approximately 3 minutes.
d. First, check the waveforms of each front heated oxygen sensor (OX1A and OX2A) at the engine speed of 2,500 to 3,000 rpm. The voltage output should alternate between 0 V and 1 V as shown.
e. Then, check the waveform of each rear heated oxygen sensor (OX1B and OX2B) likewise.
HINT: If the voltage fluctuation of either of the rear heated oxygen sensors is similar to the respective front sensors' waveform output, it may be that the three-way catalytic converter has deteriorated.
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, 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.
HINT: Hand-held tester only: It is possible the malfunctioning area can be found using the ACTIVE TEST A/F CONTROL operation. The A/F CONTROL operation can determine if the A/F sensor, heated oxygen sensor or other potential trouble areas are malfunctioning or not.
a. Perform the ACTIVE TEST A/F CONTROL operation.
HINT:
The A/F CONTROL operation lowers the injection volume 12.5% or increases the injection volume 25%.
1. Connect the hand-held tester to the DLC3 on the vehicle.
2. Turn the ignition switch to 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 the A/F CONTROL operation 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 A/F CONTROL procedure enables the technician to check and graph the voltage outputs of both the heated oxygen sensor.
To display the graph, enter ACTIVE TEST/ A/F CONTROL/USER DATA, then select "O2S B1S1 and O2S B1S2" or "O2S B2S1 and O2S B2S2" by pressing the "YES" button followed by the "ENTER" button and then the "F4" button.