Code No. P0161: Cylinder 2, 3 Oxygen Sensor (Rear) Heater System

OPERATION

Power is supplied to the heater power terminal (terminal No. 1) of the cylinder 2, 3 oxygen sensor (rear) connector from the engine control relay (terminal No. 1).
The heater (terminal No. 3) of the cylinder 2, 3 oxygen sensor (rear) connector is controlled by the power transistor in the engine-A/T-ECU (terminal No. 18).

FUNCTION

The power supply to the cylinder 2, 3 oxygen sensor (rear) heater is controlled by the ON/OFF control of the power transistor in engine-A/T-ECU.
Heating the cylinder 2, 3 oxygen sensor (rear) heater enables the cylinder 2, 3 oxygen sensor (rear) to provide good response even when the exhaust emission temperature is low.

TROUBLE JUDGMENT

Check Conditions

Engine coolant temperature is 20°C or higher.
While cylinder 2, 3 oxygen sensor (rear) heater is on.
Engine speed is approximately 50 r/min or more.
Battery positive voltage is 11 - 16 V.

Judgment Criteria

Cylinder 2, 3 oxygen sensor (rear) heater currents have continued to be 0.2 A or less, or 7.5 A or more for 4.3 seconds.

PROBABLE CAUSE

Failed cylinder 2, 3 oxygen sensor (rear) heater
Open/short circuit in cylinder 2, 3 oxygen sensor (rear) heater circuit or loose connector contact
Failed engine-A/T-ECU

DIAGNOSIS PROCEDURE

STEP 1. Connector check: B-18 cylinder 2, 3 oxygen sensor (rear) connector

Q. Is the check result normal?

Go to Step 2 .

Repair or replace.

STEP 2. Perform resistance measurement at B-18 cylinder 2, 3 oxygen sensor (rear) connector.

Disconnect connector, and measure at sensor side.
Resistance between terminal No. 1 and No. 3.

OK: 11 - 18 Ω

Q. Is the check result normal?

Go to Step 3 .

Replace cylinder 2, 3 oxygen sensor (rear).

STEP 3. Perform voltage measurement at B-18 cylinder 2, 3 oxygen sensor (rear) connector.

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?

Go to Step 5 .

Go to Step 4 .

STEP 4. Connector check: B-15X engine control relay connector

Q. Is the check result normal?

Check power supply line for open/short circuit.

Repair or replace.

STEP 5. Perform voltage measurement at C-110 engine-A/T-ECU.

Measure engine-A/T-ECU terminal voltage.
Ignition switch: ON
Voltage between terminal No. 18 and earth.

OK: System voltage

Q. Is the check result normal?

Go to Step 8 .

Go to Step 6 .

STEP 6. Connector check: C-110 engine-A/T-ECU connector

Q. Is the check result normal?

Go to Step 7 .

Repair or replace.

STEP 7. Check harness between B-18 (terminal No. 3) cylinder 2, 3 oxygen sensor (rear) connector and C-110 (terminal No. 18) engine-A/T-ECU connector.

Check earthing line for open/short circuit.

Q. Is the check result normal?

Replace engine-A/T-ECU.

Repair.

STEP 8. Connector check: C-110 engine-A/T-ECU connector

Q. Is the check result normal?

Go to Step 9 .

Repair or replace.

STEP 9. Check harness between B-18 (terminal No. 1) cylinder 2, 3 oxygen sensor (rear) connector and B-15X (terminal No. 1) engine control relay connector.

note

Before checking harness, check intermediate connector C-116, and repair if necessary.

Check power supply line for damage.

Q. Is the check result normal?

Go to Step 10 .

Repair.

STEP 10. Check harness between B-18 (terminal No. 3) cylinder 2, 3 oxygen sensor (rear) connector and C-110 (terminal No. 18) engine-A/T-ECU connector.

Check earthing line for damage.

Q. Is the check result normal?

Go to Step 11 .

Repair.

STEP 11. M.U.T.-III diagnosis code

Reconfirmation of diagnosis code.

Q. Is the diagnosis code set?

	Replace engine-A/T-ECU.

	Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points ).