Toyota Corolla (E120) 2002–2008 Repair Manual / Diagnostics / Sfi system / Catalyst system efficiency below
threshold / Circuit description
Toyota Corolla (E120): Circuit description
The ecm compares the two 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.
Monitor description
The vehicle is equipped with the two oxygen sensors (o2s). One is mounted upstream from the three–way catalytic (twc) converter (front heated oxygen sensor ”sensor 1” ), the second is mounted downstream (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.
As the twc’s efficiency degrades, its ability to store oxygen is reduced. This causes higher variations in post twc exhaust stream oxygen content and results in increased sensor 2 signal activity as shown.
When running the monitor, the ecm compares sensor1 and sensor 2 signals over a specific time to determine the twc efficiency. The ecm begins by calculating the signal length for both sensors.
Monitor strategy
Typical enabling conditions
Typical malfunction thresholds
Component operating range
Monitor result (mode 06 data)
Refer for detailed information on checking monitor status.
Confirmation driving pattern
- Connect the hand–held tester to the dlc3, or connect the probe of the oscilloscope between terminals ox1a, ox1b and e1 of the ecm connector.
- start the engine and warm it up with all the accessories switched off until the engine coolant temperature becomes stable.
- run the engine at 2,500 to 3,000 rpm for about 3 minutes.
- after confirming that the waveform of the bank 1 sensor 1 (ox) which oscillates between 0 v and 1 v under a feedback to the ecm, check the waveform of the bank 1 sensor 2 (ox).
Hint
: if there is malfunction in the system, the waveform of ”sensor 2” (oxl2) may become a similar to the one of ”sensor1” (oxl1) shown in the diagram on the left.
Other materials:
Inspection
1. Headlamp dimmer switch assy
Inspect light control switch continuity.
Measure the resistance according to the value(s) in
the table below.
Standard:
Inspect headlight dimmer switch continuity.
Measure the resistance according to the value(s) in
the tabl ...
Riding with children
Observe the following precautions
when children are
in the vehicle.
Use a child restraint system
appropriate for the child,
until the child becomes
large enough to properly
wear the vehicle's seat belt.
It is recommended that children
sit in the rear seats to
avoid accidental contact
with the ...
Overhaul
Notice: when installing, coat the parts indicated by the arrow with
power steering fluid or molybdenum disulfide lithium base grease.
1. Precaution
2. Disconnect battery negative terminal
3. Inspect center front wheel
4. Remove horn button assy
5. Remove steering wheel assy
sst 09950–50013 ...