Troubleshooting
DTC P0420 CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD (BANK 1)MONITOR DESCRIPTION
DTC Detection Condition:
Monitor Strategy:
Typical Enabling Conditions:
Typical Malfunction Thresholds:
Monitor Result (Mode 06):
The ECM uses sensors mounted before and after the three-way catalyst (TWC) to monitor its efficiency. The first sensor, an Air Fuel ratio (A/F) sensor, 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:
- Sensor 1 refers to the sensor closest to the engine assembly.
- Sensor 2 refers to the sensor farthest away from the engine assembly.
CONDITIONING A/F SENSOR AND HEATED OXYGEN SENSOR FOR TESTING
a. Connect the hand-held tester or the OBD II scan tool to the DLC3.
b. Start the engine and warm it up with all the accessories switched OFF until the Engine Coolant Temperature (ECT) is stable.
c. Run the engine at 2,500 to 3,000 rpm for about 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.
HINT:
Hand-held tester only:
- The following procedure enables a technician to identify a trouble area if there is a malfunction in front A/F sensor 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 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 ON.
3. Warm up the engine by running the engine speed at 2,500 rpm for approximately 90 seconds.
4. Enter the following menus: DIAGNOSIS / ENHANCED OBD II / ACTIVE TEST / A/F CONTROL.
5. Perform the A/F CONTROL operation with the engine idle (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: 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 a technician to check and graph the voltage outputs of both the heated oxygen sensors.
For displaying the graph, enter "ACTIVE TEST / A/F CONTROL / USER DATA", select "AFS B1S1 and O2S B1S2" by pressing "YES" and push "ENTER". Then press "F4".