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.
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.
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:
Rear wheel alignment
Inspection
1. Inspect tire
2. Measure vehicle height
Notice:
before inspecting the wheel alignment, adjust the vehicle height to the
specified value.
3. Inspect toe–in
Toe–in:
usa, canada:
Mexico:
If the toe–in is not within the specified value, inspect and replace
the suspension ...
Shift lock system (atm)
On–vehicle inspection
1. Check shift lock operation
shift the shift lever to p position.
turn the ignition switch to lock.
check that the shift lever cannot be shifted to any other
positions other than p.
turn the ignition switch to on, depress the brake pedal a ...
Engine coolant
The coolant level is satisfactory if it is between the “F” and “L” lines on the
reservoir when the engine is cold.
1 Reservoir cap
2 “F” line
3 “L” line
If the level is on or below the “L” line, add coolant up to the “F” line.
■Coolant selection
Only use “Toyota Super Long Life Coola ...