P0139

DTC P0139: Cylinder 1, 4 Heated Oxygen Sensor (rear) Circuit Slow Response

Cylinder 1, 4 Heated Oxygen Sensor (rear) Circuit Part 1:

Cylinder 1, 4 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 or the PCM (terminal No. 97) from the output terminal (terminal No. 4) of the cylinder 1, 4 heated oxygen sensor (rear).
- Terminal No. 2 of the cylinder 1, 4 heated oxygen sensor (rear) is grounded with ECM or PCM (terminal No. 106).
- The ECM or the PCM applies an offset voltage of 0.5 volt to terminal No. 2 of the cylinder 1, 4 heated oxygen sensor (rear).

TECHNICAL DESCRIPTION
- The output signal of the cylinder 1, 4 heated oxygen sensor (front) is compensated by the output signal of the cylinder 1, 4 heated oxygen sensor (rear).
- The ECM or the PCM checks for the cylinder 1, 4 heated oxygen sensor (rear) out- put voltage.

DESCRIPTIONS OF MONITOR METHODS
Cylinder 1, 4 heated oxygen sensor (rear) output voltage does not reach 0.2 volt after fuel cut operation.

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 CONDITIONS

Logic Flow Chart:

Logic Flow Chart

Check Conditions
- Engine coolant temperature is higher than 76 °C (169 °F).
- The cylinder 1, 4 heated oxygen sensor (front) is active.
- The cumulative mass airflow sensor output is higher than 1,638 g.
- Fuel is being shut off.

Judgement Criterion
- Cylinder 1, 4 heated oxygen sensor (rear) output voltage does not reach 0.2 volt for 6 seconds from fuel cut start.

OBD-II DRIVE CYCLE PATTERN
Refer to Diagnostic Function OBD-II Drive Cycle Pattern 11. OBD-II Drive Cycle

TROUBLESHOOTING HINTS (The most likely causes for this code to be set are)
- Cylinder 1, 4 heated oxygen sensor (rear) deteriorated.
- Connector damage.
- ECM failed.
- PCM 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. Using scan tool MB991958, check data list item AD: Cylinder 1, 4 Heated Oxygen Sensor (rear).

CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.

1. Connect scan tool MB991958 to the data link connector.
2. Start the engine and run at idle.
3. Set scan tool MB991958 to the data reading mode for item AD, Cylinder 1, 4 Heated Oxygen Sensor (rear).
4. Warm up the engine.
- After increasing the output voltage 0.5 volt or more by the engine revving, finish it. Then confirm that the output voltage reduces to 0.2 volt or less within 6 seconds.

5. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is the sensor operating properly?

YES: It can be assumed that this malfunction is intermittent.

NO: Replace the heated oxygen sensor (rear). Then go to Step 2.

STEP 2. 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 11. OBD-II Drive Cycle
2. Check the diagnostic trouble code (DTC).

Q: Is DTC P0139 set?

YES: Refer to DTC P0137 Cylinder 1, 4 Heated Oxygen Sensor (rear) Circuit Low Voltage, DTC P0138 Cylinder 1, 4 Heated Oxygen Sensor (rear) Circuit High Voltage.

NO: The inspection is complete.