Code No. P0135: Oxygen sensor (Front) Heater System

OPERATION

Power is supplied to the heater power terminal (terminal No. 3) of the oxygen sensor (front) connector from the engine control relay (terminal No. 4).
The heater (terminal No. 4) of the oxygen sensor (front) is controlled by the power transistor in the engine-ECU (terminal No. 79).

FUNCTION

The power supply to the oxygen sensor (front) heater is controlled by the ON/OFF control of the power transistor in the engine-ECU.
Heating the oxygen sensor (front) heater enables the 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 oxygen sensor (front) heater is on.
Battery positive voltage is 11 - 16 V.

Judgment Criterion

Oxygen sensor (front) heater current has continued to be 0.16 A or lower, or 5 A or higher for 4 seconds.

PROBABLE CAUSES

Failed oxygen sensor (front) heater
Open/short circuit and damage in oxygen sensor (front) heater circuit or loose connector contact
Failed engine-ECU

DIAGNOSIS PROCEDURE

STEP 1. Connector check: A-145 oxygen sensor (front) connector

Q. Is the check result normal?

Go to Step 2 .

Repair or replace the connector.

STEP 2. Perform resistance measurement at A-145 oxygen sensor (front) connector.

Disconnect connector, and measure at sensor side.
Resistance between terminal No. 4 and No. 3.

OK: 5 - 30 Ω (at 20°C)

Q. Is the check result normal?

Go to Step 3 .

Replace the oxygen sensor (front).

STEP 3. Perform voltage measurement at A-145 oxygen sensor (front) connector.

Disconnect connector, and measure at harness side.
Ignition switch: ON
Voltage between terminal No. 3 and earth.

OK: System voltage

Q. Is the check result normal?

Go to Step 5 .

Go to Step 4 .

STEP 4. Connector check: B-206 engine control relay connector

Q. Is the check result normal?

Check power supply line for open/short circuit.

Repair or replace the connector.

STEP 5. Perform voltage measurement at A-35 engine-ECU connector.

Disconnect engine-ECU connector, and connect special tool power plant ECU check harness (MB991987), and then measure the voltage on the check connector.
Ignition switch: ON
Voltage between terminal No. 79 and earth.

OK: System voltage

Q. Is the check result normal?

Go to Step 8 .

Go to Step 6 .

STEP 6. Connector check: A-35 engine-ECU connector

Q. Is the check result normal?

Go to Step 7 .

Repair or replace the connector.

STEP 7. Check harness between A-145 (terminal No. 4) oxygen sensor (front) connector and A-35 (terminal No. 79) engine-ECU connector.

note

Before checking harness, check intermediate connector A-36, and repair if necessary.

Check earthing line for open/short circuit.

Q. Is the check result normal?

Replace the engine-ECU then perform the variant coding (Refer to GROUP 00 - Precautions Before Service - How to Perform Variant Coding

Repair the damaged harness wire.

STEP 8. Connector check: A-35 engine-ECU connector

Q. Is the check result normal?

Go to Step 9 .

Repair or replace the connector.

STEP 9. Check harness between A-145 (terminal No. 3) oxygen sensor (front) connector and B-206 (terminal No. 4) engine control relay connector.

note

Before checking harness, check intermediate connectors A-36 and B-212, and repair if necessary.

Check power supply line for damage.

Q. Is the check result normal?

Go to Step 10 .

Repair the damaged harness wire.

STEP 10. Check harness between A-145 (terminal No. 4) oxygen sensor (front) connector and A-35 (terminal No. 79) engine-ECU connector.

note

Before checking harness, check intermediate connector A-36, and repair if necessary.

Check earthing line for damage.

Q. Is the check result normal?

Go to Step 11 .

Repair the damaged harness wire.

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

Reconfirmation of diagnosis code.

Q. Is the diagnosis code set?

	Replace the engine-ECU then perform the variant coding (Refer to GROUP 00 - Precautions Before Service - How to Perform Variant Coding ).

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