Toyota Tacoma manuals

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:

Removal and installation of fuel control parts
Place for removing and installing of fuel system parts  work in a place with good air ventilation and without anything flammable such as welder, grinder, drill, electric motor or stove in the surroundings.  Never work in a place such as a pit or nearby a pit, as there is a ...

Rear collision preparation
Concept The system reacts to vehicles approaching from behind. General information Two radar sensors in the rear bumper monitor the area behind the vehicle. When a vehicle approaches from the rear at a certain speed, the system responds as follows: Active Protection: when a collision seems to b ...

Coolant
General information Coolant consists of water and additives. Not all commercially available additives are suitable for the vehicle. Information about suitable additives is available from a dealer's service center or another qualified service center or repair shop. Safety information Warning With th ...

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