P0139

DTC P0139: Heated Oxygen Sensor Circuit Slow Response

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.73) from the output terminal (terminal No.4) of the heated oxygen sensor (rear).
- Terminal No.2 of the heated oxygen sensor (rear) is grounded with ECM (terminal No.49).

TECHNICAL DESCRIPTION
- The output signal of the heated oxygen sensor (front) is compensated by the output signal of the heated oxygen sensor (rear).
- The ECM checks for an open circuit in the heated oxygen sensor (rear) output line.

DESCRIPTIONS OF MONITOR METHODS
- Heated oxygen sensor (rear) output voltage does not change during specified go/stop operations including fuel cut are repeated.

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)
- Volume airflow sensor
- Engine coolant temperature sensor
- Intake air temperature sensor
- Barometric pressure sensor

DTC SET CONDITIONS

Logic Flow Chart:

Logic Flow Chart

Check Conditions
- Engine coolant temperature is higher than 76 degrees C (169 degrees F).
- The heated oxygen sensor (front) is active.
- The cumulative volume airflow sensor output frequency is higher than 10,000 Hz.
- Fuel is being shut off.

Judgment Criterion
- Heated oxygen sensor (rear) output voltage does not reach 0.2 volt for 6 seconds from fuel cut start.

NOTE: Monitoring stops after fuel has been shut off for more than 38 seconds.

OBD-II DRIVE CYCLE PATTERN
Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 19. OBD-II Drive Cycle Pattern Lists

TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
- Heated oxygen sensor (rear) failed.

DIAGNOSIS

Required Special Tools:
- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: V.C.I.
- MB991827: USB Cable
- MB991911: Main Harness B

STEP 1. Replace heated oxygen sensor (rear).




1. Replace heated oxygen sensor (rear).
2. Carry out a test drive with the drive cycle pattern. Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 19. OBD-II Drive Cycle Pattern Lists
3. Check the diagnostic trouble code (DTC).

Q: Is DTC P0139 set?

YES: Refer to DTC P0136 - Heated Oxygen Sensor Circuit (sensor 2) , DTC P0137 - Heated Oxygen Sensor Circuit Low Voltage (sensor 2) , DTC P0138 - Heated Oxygen Sensor Circuit High Voltage (sensor 2).

NO: The inspection is complete.