P0138
REAR HEATED OXYGEN SENSOR ( OXYGEN SENSOR 2 )
Symptom Of Fault.
The CHECK ENGINE lamp (MIL) is on.
Conditions.
P0136: All-embracing DTC.
P0138: Ignition switch in ON position. sensor voltage >1500 mV for more than 5 sec.
P0140: Diagnosis not yet performed this trip.
^ Car in motion.
^ Coolant temperature >70 °C (> 158 °F).
^ The oxygen sensor's voltage has not climbed above 0.4 V nor changed by more than 0.5 V in 500 seconds.
Diagnostic Help.
Operation of the oxygen sensor can be ascertained using an ISAT scan tool.
- Select"READ FUNCTIONS".
- Select "02S 2".
At full load the ISAT scan tool should show a reading of >0.7 V.
At fuel shut-of the ISAT scan tool should show a reading of about 0 V.
If the reference ground or sensor voltage of any of the oxygen sensors is short-circuited to battery positive (B+) in the wiring harness or in any of the oxygen sensors, DTCs P0132 and P0138 will probably both be, generated.
The engine control module inputs of the oxygen sensors are high-ohmic. If moisture gets into the connectors of some of the oxygen sensors, a diagnostic trouble code will be generated.
Checking The Wiring
Intermittent faults may occur as a result of occasional short circuits and breaks in the wiring. Jiggle the leads and in-line connectors at several places and in different directions to reveal faults in the wiring harness. Observe the multimeter, ISAT scan tool or test lamp while carrying out this check.
Diagnostic Procedure.
1. Check additional diagnostic trouble codes in the. Trionic system
- Obtain readouts of all diagnostic trouble codes using the ISAT scan tool.
Are P0132 and P0138 present?
YES: continue with point 2.
NO: Continue with point 1.
2. One of the oxygen sensor leads connected to engine control module pin 23, 70 or 47 is short-circulated to battery positive (B+) in the wiring harness or in one of the oxygen sensors.
Check the insulation of the oxygen sensors.
- Unplug the 4-pin connectors of both oxygen sensors.
- Check the resistance of both sensors
^ pins 1-3 OL (Over Load infinite resistance)
^ pins 1-4 OL (Over Load infinite resistance).
Are all readings OK?
YES: Rectify the lead between the connectors of both sensors and pin 23, 70 or 47 of the engine control module and then proceed to point 4.
NO: Change the relevant oxygen sensor and proceed to point 4.
3. Check the oxygen sensor's electrical interfaces
- Unplug the oxygen sensor's 4-pin connector.
- Replace the sensor with a conventional 1.5 V battery in good condition.
- Connect the battery's positive (+) pole to pin 4 of the connector.
- Connect the battery's -negative (-) pole to pin 3 of the connector.
- Ignition switch in ON position.
- Connect an ISAT scan tool.
- Select "READ FUNCTIONS".
- Select "O2S 2".
The ISAT scan tool must show approx. 1.4 V.
Does the ISAT scan tool show about "1.4 V"?
YES: Change the oxygen sensor and continue with point 4.
NO: Check the leads between pin 4 of the connector and pin 70 of the engine control module and between pin 3 of the connector and pin 47 of the engine control module for continuity or shorting and rectify them as necessary. Then continue with point 4.
4. Final check:
- Clear the diagnostic trouble code.
- Implementation of driving cycle:
Start the engine and run it at idling speed until the temperature of the coolant exceeds 60°C (140°F) or for at least 1 minute if this temperature is reached earlier.
- Connect an ISAT scan tool.
- Select "READ FUNCTIONS".
- Select "025 2".
- Drive the car and check that the ISAT scan tool readings are:
^ >0.7 V at full load.
^ about 0 V at fuel shut-of in connection with engine braking (manual gearbox: 3rd, 4th or 5th gear and engine speed above 2,000 rpm).
Are the readings OK?
YES: Continue at "Before Replacing a Control Module". Component Tests and General Diagnostics
NO: The remedial measure taken was correct.