Monitor description
The ecm uses sensors mounted in front of and behind the three-way catalytic converter (twc) to monitor its efficiency.
The first sensor, the air-fuel ratio (a/f) sensor, sends pre-catalyst information to the ecm. The second sensor, the heated oxygen (ho2) sensor, sends post-catalyst information to the ecm.
In order to detect any deterioration in the twc, the ecm calculates the oxygen storage capacity (osc) of the twc. This calculation is based on the voltage output of the ho2 sensor while performing active airfuel ratio control, rather than the conventional detecting method, which uses the locus ratio.
The osc value is an indication of the oxygen storage capacity of the twc. When the vehicle is being driven with a warm engine, active air-fuel ratio control is performed for approximately 15 to 20 seconds.
When it is performed, the ecm deliberately sets the air-fuel ratio to lean or rich levels. If the rich-lean cycle of the ho2 sensor is long, the osc becomes greater. There is a direct correlation between the oscs of the ho2 sensor and the twc.
The ecm uses the osc value to determine the state of the twc. If any deterioration has occurred, it illuminates the mil and sets the dtc.
Monitor strategy
Typical enabling conditions
Typical malfunction thresholds
Monitor result
Refer to checking monitor status (see page es-17).
Confirmation driving pattern
Hint:
Performing this confirmation pattern will activate the catalyst monitor. This is very useful for verifying the completion of a repair.
Hint:
If cat cmpl does not change to compl, and any pending dtcs fail to set, extend the driving time.
Conditioning for sensor testing
Hint:
Perform the operation with the engine speeds and time durations described below prior to checking the waveforms of the a/f and ho2 sensors. This is in order to activate the sensors sufficiently to obtain the appropriate inspection results.
Hint:
Inspection procedure
Hint:
Read freeze frame data using the intelligent tester. Freeze frame data records the engine condition when malfunctions are detected. When troubleshooting, freeze frame data can help determine if the vehicle was moving or stationary, 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:
If any dtcs other than p0420 are output, troubleshoot those dtcs first.
Result: a/f sensor reacts in accordance with increases and decreases in fuel injection volume: +25 % = rich output: less than 3.0 V
-12.5 % = Lean output: more than 3.35 V
Notice:
The a/f sensor has an output delay of a few seconds and the ho2 sensor has a maximum output delay of approximately 20 seconds.
Following the a/f control procedure enables technicians to check and graph the voltage outputs of both the a/f and ho2 sensors.
To display the graph, select the following menu items on the tester: diagnosis / enhanced obd ii / active test / a/f control / user data / afs b1 s1 and o2s b1 s2; then press the yes button and then the enter button followed by the f4 button.
Ok: no gas leakage.
Replace three-way catalytic converter (both front and rear catalysts (front exhaust pipe))
Ok: no gas leakage.
Precaution
Tire pressure warning system precaution
When the tire pressure warning light turns on,
immediately check the tire pressure of the tire and
adjust it to the specified value. (When the tire
pressure warning light circuit is open, the tire
pressure warning light flashes for 1 minut ...
Pig power supply voltage malfunction
Description
When a problem occurs in the system, the power source relay circuit is shut
off to stop the power assist.
Wiring diagram
Inspection procedure
Read value of intelligent tester (pig power supply)
Connect the intelligent tester (with can vim) to the
dlc3.
Turn ...
Data list / active test
Read data list
Hint:
Using the intelligent tester's data list allows switch,
actuator and other item values to be read without
removing any parts. Reading the data list early in
troubleshooting is one way to save time.
Connect the intelligent tester (with can vim) to the
dlc3.
Turn ...