Code No. P0138: Oxygen Sensor (rear) Circuit High Voltage




OPERATION



  • The sensor signal is inputted to the engine-ECU connector terminal O2RL from the oxygen sensor (rear) output terminal.
  • The oxygen sensor (rear) connector terminal is earthed with engine-ECU connector terminal ORLE.
  • The engine-ECU connector terminal ORLE applies an offset voltage of 0.5 V to the oxygen sensor (rear) connector terminal.

FUNCTION



  • The oxygen sensor (rear) converts the concentration of oxygen in the exhaust emission into a voltage and inputs the signal to the engine-ECU.
  • When the air-fuel ratio is richer than the theoretical air-fuel ratio, the oxygen sensor (rear) outputs a voltage of about 1 V. When it is leaner than the theoretical air-fuel ratio, it outputs a voltage of about 0 V.
  • In response to the signal, the engine-ECU controls the fuel injection amount so that the air-fuel ratio can be equivalent to the theoretical air-fuel ratio.

TROUBLE JUDGMENT


Check Conditions
  • More than 2 seconds have passed since the engine starting sequence was completed.
  • Oxygen sensor (rear) offset voltage is more than 0.4 V and is less than 0.6 V.
Judgement Criterion
  • Oxygen sensor (rear) output voltage is more than 1.2 V for 2 seconds.

FAIL-SAFE AND BACKUP FUNCTION



  • None

PROBABLE CAUSES



  • Failed oxygen sensor (rear)
  • Short circuit in oxygen sensor (rear) circuit or loose connector contact
  • Failed engine-ECU

DIAGNOSIS PROCEDURE


STEP 1. M.U.T.-III data list



  • Data list reference table (Refer to ).

  1. Item AD: Oxygen sensor (rear)

Q. Are the check results normal?

Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).
Go to Step 2.

STEP 2. Check harness between oxygen sensor (rear) connector terminal and engine-ECU connector terminal O2RL.



  • Check output line for short circuit.

Q. Is the check result normal?

Go to Step 3.
Repair or replace the connector, or repair the damaged harness wire.

STEP 3. Check harness between oxygen sensor (rear) connector terminal and engine-ECU connector terminal ORLE.



  • Check earthing line for short circuit.

Q. Is the check result normal?

Go to Step 4.
Repair or replace the connector, or repair the damaged harness wire.

STEP 4. M.U.T.-III data list



  • Data list reference table (Refer to ).

  1. Item AD: Oxygen sensor (rear)

Q. Is the check result normal?

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