P0420
DTC P0420 CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD (BANK 1)MONITOR DESCRIPTION
DTC Detecting Condition:
Monitor Strategy:
Typical Enabling Conditions:
Typical Malfunction Thresholds:
The ECM uses sensors mounted before and after the three-way catalyst (TWC) to monitor it's efficiency. The first sensor, an air-fuel ratio (A/F) sensor 1, sends pre-catalyst A/F ratio information to the ECM. The second sensor, a heated oxygen sensor (O2S) 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 heated oxygen sensor 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 monitor, the ECM compares sensor 1 signals (A/F sensor) over a specific amount of time to determine catalyst efficiency. The ECM begins by calculating the signal length for both sensors (for the rear oxygen sensor, the ECM uses the output voltage signal length). If the oxygen sensor output voltage signal length is greater than the threshold (threshold is calculated based on the A/F sensor signal length), the ECM concludes that the catalyst is malfunctioning. The ECM will turn on the MIL and a DTC will be set.
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 RESULT
Refer to CHECKING MONITOR STATUS for detailed information.
The test value and test limit information are described as shown in the table. Check the monitor result and test values after performing the monitor drive pattern.
- TID (Test Identification Data) is assigned to each emissions-related component.
- TLT (Test Limit Type):
If TLT is 0, the component is malfunctioning when the test value is higher than the test limit. If TLT is 1, the component is malfunctioning when the test value is lower than the test limit.
- CID (Component Identification Data) is assigned to each test value.
- Unit Conversion is used to calculate the test value indicated on generic OBD II scan tools.
CONDITIONING THE A/F SENSOR AND HEATED OXYGEN SENSOR FOR TESTING
a. Connect the OBD II scan tool or 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 is stable.
c. Run the engine at 2,500 to 3,000 rpm for approximately 3 minutes.
d. When alternating the engine between 3,000 rpm for 2 seconds and 2,000 rpm for 2 seconds, check the waveform of the oxygen sensor (bank 1 sensor 2).
Step 1:
Step 2 - 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.
NOTE: On the damaged bank, replace both the front catalyst and rear catalyst.
HINT:
Hand-held tester only:
- The ACTIVE TEST A/F CONTROL procedure enables the technician to identify a trouble area if malfunction in A/F sensors, front or rear heated oxygen sensors other than the catalyst converter, or the malfunction that indicates the actual air-fuel ratio extremely RICH or LEAN.
- It is possible to locate the problem area by performing ACTIVE TEST A/F CONTROL (heated oxygen sensor or other trouble areas can be distinguished).
a. Perform 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: A/F sensor reacts in accordance with increase and decrease of injection volume:
+25 % -> RICH output: Less than 3.0 V
-12.5 % -> LEAN output: More than 3.35 V
Heated oxygen sensor reacts in accordance with 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 A/F sensor output has a few seconds of delay and the heated oxygen sensor output has about 20 seconds of delay at maximum.
The following of A/F CONTROL procedure enables the technician to check and graph the voltage outputs of both the heated oxygen sensors.
To display the graph, enter ACTIVE TEST / A/F CONTROL / USER DATA, then select "AFS B1S1 and O2S B1S2" or "AFS B2S1 and O2S B2S2" by pressing the "YES" button followed by the "ENTER" button and then the "F4" button.