OPERATION
- Power is supplied to the heater power terminal (terminal No. 1) of the Cylinder 1, 4 oxygen sensor (front) connector from the engine control relay (terminal No. 1).
- The heater (terminal No. 3) of the Cylinder 1, 4 oxygen sensor (front) connector is controlled by the power transistor in the engine-A/T-ECU (terminal No. 25).
FUNCTION
- The power supply to the cylinder 1, 4 oxygen sensor (front) heater is controlled by the ON/OFF control of the power transistor in the engine-A/T-ECU.
- Heating the cylinder 1, 4 oxygen sensor (front) heater enables the cylinder 1, 4 oxygen sensor (front) to provide good response even when the exhaust emission temperature is low.
TROUBLE JUDGMENT
Check Conditions
- 60 seconds have elapsed since the previous monitoring started.
- Engine coolant temperature is
20°C or higher.
- While cylinder 1, 4 oxygen sensor (front) heater is on.
- Battery positive voltage is 11 - 16 V.
Judgment Criterion
- Cylinder 1, 4 oxygen sensor (front) heater current has continued to be 0.16 A or lower, or 7.5 A or higher for 4 seconds.
PROBABLE CAUSE
- Failed cylinder 1, 4 oxygen sensor (front) heater
- Open/short circuit in cylinder 1, 4 oxygen sensor (front) circuit or loose connector contact
- Failed engine-A/T-ECU
)
Q: Is the check result normal?
YES:
Go to Step 2 
.NO: Repair.
- Disconnect connector, and measure at sensor side.
- Resistance between terminal No. 1 and No. 3.
OK: 4.5 -
8.0 Ω
Q: Is the check result normal?
YES:
Go to Step 3 .NO: Replace cylinder 1, 4 oxygen sensor (front).
- Disconnect connector, and measure at harness side.
- Ignition switch: ON
- Voltage between terminal No. 1 and earth.
OK: System voltage
Q: Is the check result normal?
YES:
Go to Step 5 .NO: Go to Step 4
.)
Q: Is the check result normal?
YES:
- Check and repair harness between B-122 (terminal No. 1) cylinder 1, 4 oxygen sensor (front) connector and B-17X (terminal No. 1) engine control relay connector.
- Check power supply line for open/short circuit.
)
- Measure engine-A/T-ECU terminal voltage.
- Ignition switch: ON
- Voltage between terminal No. 25 and earth.
OK: System voltage
Q: Is the check result normal?
YES:
Go to Step 8 .NO: Go to Step 6
.
Q: Is the check result normal?
YES:
Go to Step 7 .NO: Repair.
- Check earthing line for open/short circuit.
Q: Is the check result normal?
YES:
Replace engine-A/T-ECU.NO: Repair.
Q: Is the check result normal?
YES:
Go to Step 9 .NO: Repair.
- Check power supply line for damage.
Q: Is the check result normal?
YES:
Go to Step 10 .NO: Repair.
- Check earthing line for damage.
Q: Is the check result normal?
YES:
Go to Step 11 .NO: Repair.
