P0138

DTC P0138: Heated Oxygen Sensor Circuit High Voltage (bank 1, sensor 2)

Right Bank Heated Oxygen Sensor (Rear) Circuit:

CIRCUIT OPERATION
- A voltage corresponding to the oxygen concentration in the exhaust gas is sent to the ECM (terminal No. 56) from the output terminal (terminal No. 4) of the right bank heated oxygen sensor (rear).
- Terminal No. 2 of the right bank heated oxygen sensor (rear) is grounded with ECM (terminal No. 57).
- The ECM applies an offset voltage of 0.5 volt to terminal No. 2 of the right bank heated oxygen sensor (rear).

TECHNICAL DESCRIPTION
- The output signal of the right bank heated oxygen sensor (front) is compensated by the output signal of the right bank heated oxygen sensor (rear).
- The ECM checks for the right bank heated oxygen sensor (rear) output voltage.

DESCRIPTIONS OF MONITOR METHODS
Right bank heated oxygen sensor (rear) output voltage is over the specified range.

MONITOR EXECUTION
Continuous

MONITOR EXECUTION CONDITIONS (Other monitor and Sensor)

Other Monitor (There is no temporary DTC stored in memory for the item monitored below)
- Not applicable

Sensor (The sensor below is determined to be normal)
- Engine coolant temperature sensor

DESCRIPTIONS OF MONITOR METHODS
Right bank heated oxygen sensor (rear) output voltage is over the specified range.

MONITOR EXECUTION
Continuous

MONITOR EXECUTION CONDITIONS (Other monitor and Sensor)

Other Monitor (There is no temporary DTC stored in memory for the item monitored below)
- Heated oxygen sensor (front) monitor
- Heated oxygen sensor (front) inactive monitor
- Heated oxygen sensor offset voltage monitor
- Heated oxygen sensor (front) heater monitor
- Heated oxygen sensor (rear) heater monitor
- Air/fuel ratio feedback monitor

Sensor (The sensor below is determined to be normal)
- Mass airflow sensor
- Engine coolant temperature sensor
- Intake air temperature sensor
- Barometric pressure sensor

DTC SET CONDITION

Logic Flow Chart:

Check Conditions
- 2 seconds or more have passed since the engine starting sequence was completed.
- Heated oxygen sensor off set voltage is between 0.4 and 0.6 volt.

Judgement Criterion
- Right bank heated oxygen sensor (rear) output voltage has continued to be 1.8 volts or higher for 2 seconds.

OBD-II DRIVE CYCLE PATTERN
Refer to MFI Diagnostic Function-OBD-II Drive Cycle-Pattern 24. OBD-II Drive Cycle

TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
- Connector damage.
- Harness damage
- ECM failed.

DIAGNOSIS

Required Special Tools:
- MB991958: Scan tool (M.U.T.-III Sub Assembly)
- MB991824: V.C.I.
- MB991827: USB Cable
- MB991910: Main Harness A

STEP 1. Check harness connector B-02 at the right bank heated oxygen sensor (rear) and harness connector B-10 at ECM for damage.

Q: Is the harness connector in good condition?

YES : Go to Step 2.

NO : Repair it. Refer to General (Electrical), Harness Connector Inspection. Then go to Step 4.

STEP 2. Check for short circuit to power supply between the right bank heated oxygen sensor (rear) connector B-02 (terminal No. 4) and the ECM connector B-10 (terminal No. 56).

Q: Is the harness wire in good condition?

YES : Go to Step 3.

NO : Repair it. Then go to Step 4.

STEP 3. Check the trouble symptoms.

1. Carry out a test drive with the drive cycle pattern. Refer to MFI Diagnostic Function-OBD-II Drive Cycle-Pattern 24. OBD-II Drive Cycle
2. Check the diagnostic trouble code (DTC).

Q: Is DTC P0138 set?

YES : Replace the ECM. When the ECM is replaced,register the ID code. Refer to Diagnosis-ID Codes Registration Judgment Table [Vehicles with KOS] or Diagnosis-ID Codes Registration Judgment Table [Vehicles with WCM]. Then go to Step 4.

NO : It can be assumed that this malfunction is intermittent. Refer to General (Body and Chassis), How to Use Troubleshooting/Inspection Service Points-How to Cope with Intermittent Malfunctions.

STEP 4. Test the OBD-II drive cycle.

1. Carry out a test drive with the drive cycle pattern. Refer to MFI Diagnostic Function-OBD-II Drive Cycle-Pattern 24. OBD-II Drive Cycle
2. Check the diagnostic trouble code (DTC).

Q: Is DTC P0138 set?

YES : Retry the troubleshooting.

NO : The inspection is complete.