P0138
DTC P0138: Heated Oxygen Sensor Circuit High Voltage (bank 1, sensor 2)Right Bank Heated Oxygen Sensor (Rear) Circuit Part 1:
Right Bank Heated Oxygen Sensor (Rear) Circuit Part 2:
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 heater (front) monitor
Heated oxygen sensor heater (rear) 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:
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 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.
DIAGNOSTIC
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. 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 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 ID Code Registration Judgment Table
NO: It can be assumed that this malfunction is intermittent.
STEP 4. Test the OBD-II drive cycle.
1. Carry out a test drive with the drive cycle pattern. Refer to 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.