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:
Automatic transaxle assy (atm)
Precaution
The automatic transaxle is composed of highly precision–finished
parts, necessitating careful
inspection before reassembly because even a small nick could cause fluid
leakage or affect
the performance. The instructions here are organized so that you work on
only o ...
Replacement
Hint:
installation is in the reverse order of the removal. But the installation is
indicated only when it has a point.
1. Remove luggage compartment door cover
2. Remove rear spoiler
remove the 2 screws.
disconnect the wire harness connector.
put protective tape.
&nb ...
Inspection procedure
1 Inspect terminal voltage(od – body ground)
Disconnect the cruise control ecu connector.
turn the ignition switch to the on position.
measure the voltage between terminal od of cruise control
ecu and body ground.
Standard:
2 Inspect terminal voltage(od1 – bod ...