Code No. P0157: Left Bank Oxygen Sensor (rear) Circuit Low Voltage
OPERATION
- The sensor signal is inputted to the engine-ECU connector terminal O2RL from the left bank oxygen sensor (rear) output terminal.
- The left bank oxygen sensor (rear) is earthed with engine-ECU connector terminal O2VE.
- The engine-ECU connector terminal O2VE applies an offset voltage of 0.5 V to the left bank oxygen sensor (rear) connector terminal.
FUNCTION
- The left bank 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 left bank 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 JUDGEMENT
Check Conditions
- Left bank oxygen sensor (rear) offset voltage is more than 0.4 V and is less than 0.6 V.
- Battery positive voltage is more than 11 V and is less than 16.5 V.
- More than 3 minutes have passed since the engine starting sequence was completed.
Judgement Criterion
- Left bank oxygen sensor (rear) output voltage is less than 0.2 V for 2 seconds.
FAIL-SAFE AND BACKUP FUNCTION
PROBABLE CAUSES
- Failed left bank oxygen sensor (rear)
- Open/short circuit or harness damage in left bank oxygen sensor (rear) circuit or loose connector contact
- Failed engine-ECU
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STEP 1. M.U.T.-III data list
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- Data list reference table (Refer to
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- Item AF: Left bank oxygen sensor (rear)
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Q.
Is the check result normal?
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 Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).
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 Go to Step 2.
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STEP 2. Voltage measurement at left bank oxygen sensor (rear) connector (O2VE line).
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(1)Disconnect the connector, and measure at the wiring harness side.
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(3)Check the voltage between the left bank oxygen sensor (rear) connector (O2VE line) and body earth.
OK: 0.4 - 0.6 V
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Q.
Is the check result normal?
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Go to Step 5.
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Go to Step 3.
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STEP 3. Check of short to earth and open circuit in O2VE line between left bank oxygen sensor (rear) connector and engine-ECU connector.
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Q.
Is the check result normal?
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Go to Step 4.
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Repair the connector(s) or wiring harness.
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STEP 4. M.U.T.-III data list
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- Data list reference table (Refer to ).
- Item AF: Left bank oxygen sensor (rear)
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Q.
Is the check result normal?
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Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).
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Replace the engine-ECU.
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STEP 5. Check of harness damage in O2VE line between left bank oxygen sensor (rear) connector and engine-ECU connector.
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Q.
Is the check result normal?
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Go to Step 6.
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Repair the connector(s) or wiring harness.
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STEP 6. Voltage measurement at left bank oxygen sensor (rear) connector (O2RL line).
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(1)Use special tool test harness (MB991658) to connect connector, and measure at pick-up harness.
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(2)Transmission: 2nd speed
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(3)Drive with wide open throttle
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(4)Engine: 3,500 r/min or more
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(5)Check the voltage between the left bank oxygen sensor (rear) connector (O2RL line) and body earth.
OK:
The output voltage should be 1.1 - 1.5 V.
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Q.
Is the check result normal?
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Go to Step 8.
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Go to Step 7.
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STEP 7. Check left bank oxygen sensor (rear) itself.
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- Left bank oxygen sensor (rear) check (Refer to ).
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Q.
Is the check result normal?
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Repair or replace the connector(s), or check and repair the harness of short circuit to earth in O2RL line between left bank oxygen sensor (rear) connector and engine-ECU connector.
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Replace the left bank oxygen sensor (rear).
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STEP 8. Check of open circuit and damage in O2RL line between left bank oxygen sensor (rear) connector and engine-ECU connector.
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Q.
Is the check result normal?
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Go to Step 4.
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Repair the connector(s) or wiring harness.
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