Code No. P0136: Oxygen Sensor (Rear) System

OPERATION

• The sensor signal is inputted to the engine-ECU (terminal No. 100) from the oxygen sensor (rear) output terminal (terminal No. 1).
  
• The oxygen sensor (rear) (terminal No. 2) is earthed with engine-ECU (terminal No. 99).
  

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.
  
• Based on this signal, the engine-ECU corrects the deviation in the signal that is output by the oxygen sensor (front).
  

TROUBLE JUDGMENT

• Above 3 minutes later after the engine has started up.
  
• The engine coolant temperature is approximately 82°C or higher.
  
• The engine speed is 1200 r/min or more.
  
• The monitoring time is 10 seconds.
  

• When the oxygen sensor (rear) output voltage is 0.2 V or less and a power voltage of 5 V is applied to the oxygen sensor (rear) in the engine-ECU, the sensor output voltage is 4.5 V or more.
  
• To be monitored once per driving cycle.
  

• 2 seconds later after lack of circuit continuity is detected.
  
• When the front oxygen sensor is normally operated.
  

• When the air-fuel ratio is rich, the oxygen sensor (front) output voltage is 0.5 V or more.
  
• The oxygen sensor (rear) output voltage is less than 0.1 V.
  
• The difference between the maximum and the minimum of the oxygen sensor (rear) output is 0.078 V or less.
  

PROBABLE CAUSES

• Failed oxygen sensor (rear)
  
• Open or shorted oxygen sensor (rear) circuit, harness damage, or connector damage
  
• Failed engine-ECU
  

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

	Go to Step 2 .

Q. Is the check result normal? Go to Step 3 . Repair or replace the connector.

Disconnect connector, and measure at harness side. Resistance between terminal No. 2 and earth. OK: Continuity (2 Ω or less) Q. Is the check result normal? Go to Step 7 . Go to Step 4 .

Q. Is the check result normal? Go to Step 5 . Repair or replace the connector.

Check earthing line for open circuit and damage. Q. Is the check result normal? Go to Step 6 . Repair the damaged harness wire.

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

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

Use special tool test harness (MB991658) to connect connector, and measure at pick-up harness. Engine: After warm-up Transmission: Neutral Voltage between terminal No. 1 and earth. OK: When the engine is 2,500 r/min, the output voltage should repeat 0 to 0.8 V alternately Q. Is the check result normal? Go to Step 10 . Go to Step 8 .

	Go to Step 9 .

	Replace the oxygen sensor (rear).

Q. Is the check result normal? Check and repair harness between C-24 (terminal No. 1) oxygen sensor (rear) connector and A-09 (terminal No. 100) engine-ECU connector. Check output line for short circuit. Repair or replace the connector.

Disconnect engine-ECU connector, and connect special tool power plant ECU check harness (MB991987), and then measure the voltage on the check connector. Transmission: Neutral Engine: After warm-up Voltage between terminal No. 100 and earth. OK: When the engine is 2,500 r/min, the output voltage should repeat 0 to 0.8 V alternately. Q. Is the check result normal? Go to Step 12 . Go to Step 11 .

Q. Is the check result normal? Check and repair harness between C-24 (terminal No. 1) oxygen sensor (rear) connector and A-09 (terminal No. 100) engine-ECU connector. Check output line for open circuit and damage. Repair or replace the connector.

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