Code No. P0037: Oxygen Sensor (rear) Heater Circuit Low Input










OPERATION



  • Power is supplied to the heater power terminal (terminal No. 1) of the oxygen sensor (rear) connector from the engine control relay (terminal No. 2).
  • The heater (terminal No. 2) of the oxygen sensor (rear) connector is controlled by the power transistor in the engine-ECU (terminal No. 35).

FUNCTION



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

TROUBLE JUDGMENT


Check Conditions
  • More than 2 seconds have passed since the engine starting sequence was completed.
  • While the oxygen sensor (rear) heater is on.
  • Battery positive voltage is more than 11 V and is less than 16.5 V.
Judgement Criterion
  • The oxygen sensor (rear) heater current is less than 0.17 A for 2 seconds.
Check Conditions
  • More than 2 seconds have passed since the engine starting sequence was completed.
  • While the oxygen sensor (rear) heater is off.
  • Battery positive voltage is more than 11 V and is less than 16.5 V.
Judgement Criterion
  • The oxygen sensor (rear) heater voltage is less than 2.0 V for 2 seconds.

FAIL-SAFE AND BACKUP FUNCTION



  • None

PROBABLE CAUSES



  • Failed oxygen sensor (rear) heater
  • Open/short circuit or harness damage in oxygen sensor (rear) heater circuit or loose connector contact
  • Failed engine-ECU

DIAGNOSIS PROCEDURE

STEP 1. Connector check: D-31 oxygen sensor (rear) connector

Q. Is the check result normal?
Go to Step 2 .
Repair or replace the connector.

STEP 2. Perform resistance measurement at D-31 oxygen sensor (rear) connector.

  • Disconnect connector, and measure at sensor side.
  • Resistance between terminal No. 1 and No. 2.
OK: 4.5 - 8.0 Ω (at 20°C)

Q. Is the check result normal?
Go to Step 3 .
Replace the oxygen sensor (rear).

STEP 3. Perform voltage measurement at D-31 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: A-33X engine control relay connector

Q. Is the check result normal?

    Check intermediate connectors C-31, C-30 and repair if necessary. If intermediate connectors are normal, check and repair harness between D-31 (terminal No. 1) oxygen sensor (rear) connector and A-33X (terminal No. 2) engine control relay connector.

    • Check power supply line for open/short circuit.
Repair or replace the connector.

STEP 5. Connector check: B-08 engine-ECU connector

Q. Is the check result normal?
Go to Step 6 .
Repair or replace the connector.

STEP 6. Perform voltage measurement at B-08 engine-ECU connector.

  • Disconnect connector, and measure at harness side.
  • Ignition switch: ON
  • Voltage between terminal No. 35 and earth.
OK: System voltage

Q. Is the check result normal?
Go to Step 7 .

    Check intermediate connectors C-29, A-11, and repair if necessary. If intermediate connectors are normal, check and repair harness between D-31 (terminal No. 2) oxygen sensor (rear) connector and B-08 (terminal No. 35) engine-ECU connector.

    • Check earthing line for open/short circuit.

STEP 7. Check harness between D-31 (terminal No. 2) oxygen sensor (rear) connector and B-08 (terminal No. 35) engine-ECU connector.
note Before checking harness, check intermediate connectors C-29, A-11, and repair if necessary.

  • Check earthing line for damage.

Q. Is the check result normal?
Go to Step 8 .
Repair the damaged harness wire.

STEP 8. Connector check: A-33X engine control relay connector

Q. Is the check result normal?
Go to Step 9 .
Repair or replace the connector.

STEP 9. Check harness between D-31 (terminal No. 1) oxygen sensor (rear) connector and A-33X (terminal No. 2) engine control relay connector.
note Before checking harness, check intermediate connectors C-31, C-30 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. M.U.T.-III diagnosis code

  • Reconfirmation of diagnosis code.

Q. Is diagnosis code set?
Replace the engine-ECU.
Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).