Diagnostic Trouble Code (DTC) P0138

Rear Heated Oxygen Sensor High Voltage

                                        

                                   

                                                                         Features of the Circuit

 

  • A voltage approximately of 450mm volts is generated by the ECM between the ECM terminals 44 and 13.
  • If the Exhaust Is RICH:    The Heated oxygen (O2) sensor is devised to alter the voltage  between a range of about 1volt.
  • If the Exhaust Is POOR:  The Heated oxygen (O2) sensor is devised to alter the  voltage between a range of about 100mm volt.
  • The Heated O2 sensor acts quite like an open circuit and does not generate any voltage when it is below 360°C(600°F).
  • An "open loop" operation is created by an open O2 sensor circuit or a cold O2 sensor                           

 

 

                                                 QUESTION:  When Does DTC Set?

                                                ANSWER:  The Heated oxygen sensor voltage is more than 1.2V.

 

Task Boosted When DTC sets

When Does DTC clear?

1) The Malfunction Indicator Lamp (MIL) will be seen glowing after three failed repetitive trips.

 

1)   The MIL will stop work after four repetitive ignition cycles where the diagnostic functions flawlessly.

 

2) The ECM is devised to record operating conditions at the time the diagnostic fails which will be stored in the Freeze Frame and Failure Records will be boosted.

 

2)  A history DTC will clear after 40 consecutive warm-up cycles without a fault

3) A history DTC is stored.

 

3)  The Scan Tool can be made use of in order to clear all DTCs

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4) Disconnecting the ECM battery feed for more than 10 seconds

 

 

Diagnostic Assistance:

  • Here the circuit is devised so that the normal scan tool voltage fluctuates between 0.1 volts and 0.9 volts while it is in closed loop.
  • It is advised that you inspect the oxygen (O2) sensor wire where the  O2 sensor could  be placed inaccurately and contacting the exhaust manifold.
  • Also look for an intermittent ground in the wire found between the O2 sensor and the ECM.
  • Execute an injector balance test to ensure that a restricted fuel injector is not responsible for a lean condition.
  • If any vacuum of crankcase leaks exists then  a lean running condition will prevail.
  • Outside air may be sucked into the exhaust and past the sensor if an exhaust manifold gasket leak of a cracked exhaust is found to exist.

 

                                                                       STEPS TO DETERMINE THIS DTC

DTC P0138 - Rear Heated Oxygen Sensor High Voltage

 

Step

Task

Positive

Negative

1

Carry out an EOBD System Check.

 

Task Complete?

Look up Step 2

Look up "On-Board Diagnostic System Check"

2

1) Keeping the engine OFF switch ON the ignition

2)  Now insert a scan tool.

3) Control the engine at normal operating temperature.

4) Let the engine run at 1,200rpm.

NOTE: The value at this juncture should  be>1.2V

 

Do you notice that the scan tool the Heated oxygen (O2) sensor1 voltage is within the specified parameters?

Look up Step 3

Look up Step 6

3

1)  Take the ignition switch to LOCK mode.

2)    De-link the Heated O2 sensor connector and ECM connector.

3)   Examine the Heated O2 sensor wire between the Heated O2 sensor connector terminal 1 and ECM connector terminal 14 to probe for a short to ground.

Did you come across any problem?

Look up Step 4

Look up Step 5

4

1) Correct the wire of the connector terminal if needed.

2) Clear all existing DTCs from the ECM.

3) Test the vehicle by running on road.

4) Run the diagnostic system check.

Work over?

The System of the engine is perfect.

-

5

1) LOCK the ignition switch.

2) Substitute the Heated O2 sensor.

3) Test the vehicle by running on road.

4) Repeat the diagnostic system check.

Task complete?

Look up Step 7

-

6

1) LOCK the ignition switch.

2) Substitute the ECM.

3) Test the vehicle by running on road.

4) Repeat the diagnostic system check.

Task complete?

Look up Step 7

-

7

Probe whether any additional DTCs remain set.

 

Do you see any undiagnosed DTCs being exhibited?

Look up applicable DTC table

The System of the engine is perfect.