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Toyota Corolla Repair Manual: 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.

Airfuel 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 threeway 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 twcs efficiency degrades, its ability to store oxygen is reduced.

As the twcs 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

Monitor strategy

Typical enabling conditions

Typical enabling conditions

Typical malfunction thresholds

Typical malfunction thresholds

Component operating range

Component operating range

Monitor result (mode 06 data)

Monitor result (mode 06 data)

Refer  for detailed information on checking monitor status.

Refer  for detailed information on checking monitor status.

Confirmation driving pattern

  1. Connect the handheld tester to the dlc3, or connect the probe of the oscilloscope between terminals ox1a, ox1b and e1 of the ecm connector.
  2.  start the engine and warm it up with all the accessories switched off until the engine coolant temperature becomes stable.
  3.  run the engine at 2,500 to 3,000 rpm for about 3 minutes.
  4.  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.

Inspection procedure

Catalyst system efficiency below threshold
Dtc p0420 catalyst system efficiency below threshold (bank 1) ...

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, it is usefu ...

Other materials:

Circuit description
Shifting from 1st to o/d is performed in combination with on and off of the shift solenoid valve s1 and s2 controlled by ecm. If an open or short circuit occurs in either of the solenoid valves, the ecm controls the remaining normal solenoid valve to allow the vehicle to be operated smoothly ...

Terminals of ecu
1. Inspect integration relay Disconnect the connector and check the continuity of each terminal of the disconnected connector. Standard : If the result is not as specified, the vehicles side may malfunction. Reconnect the connector and check each terminal. Standard: If th ...

Inspection procedure
1 Check p/t squib(rh) circuit(airbaga sensor assy center front seat outer belt assy rh) Disconnect the negative () terminal cable from the battery, and wait at least for 90 seconds.  disconnect the connectors between the airbag sensor assy center and the seat belt pretensioner ...

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