DTC P0139: Heated Oxygen Sensor (rear) Circuit Slow Responce

CIRCUIT OPERATION

A voltage corresponding to the oxygen concentration in the exhaust gas is sent to the ECM (terminal No. 40) from the output terminal (terminal No. 3) of the heated oxygen sensor (rear).
Terminal No. 4 of the heated oxygen sensor (rear) is grounded with ECM (terminal No. 41).
The ECM applies an offset voltage of 0.5 volt to terminal No. 4 of the heated oxygen sensor (rear).

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 the heated oxygen sensor (rear) output voltage.

DESCRIPTIONS OF MONITOR METHODS

MONITOR EXECUTION

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) heater monitor
Heated oxygen sensor (rear) heater monitor
Heated oxygen sensor (front) inactive monitor
Heated oxygen sensor offset voltage 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

Check Conditions

Engine coolant temperature is more than 76°C (169°F).
The heated oxygen sensor (front) is active.
The cumulative mass airflow sensor output is more than 1,638 g.
Fuel is being shut off.
Heated oxygen sensor (rear) output voltage is more than 0.5 volt when fuel cut is started.

Judgement Criterion

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

Heated oxygen sensor (rear) output voltage does not reach 0.2 volt for 1 second from 0.4 volt while fuel is being shut off.

note

Monitoring stops after fuel has been shut off for 64 seconds or more.

FAIL-SAFE AND BACKUP FUNCTION

None

OBD-II DRIVE CYCLE PATTERN

TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)

Heated oxygen sensor (rear) deteriorated.
Connector 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. Using scan tool MB991958, check data list item AD: 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, 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?

It can be assumed that this malfunction is intermittent. Refer to GROUP 00, How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions

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 10

(2)Check the diagnostic trouble code (DTC).

Q. Is DTC P0139 set?

	Refer to DTC P0137 - Heated Oxygen Sensor (rear) Circuit Low Voltage , DTC P0138 - Heated Oxygen Sensor (rear) Circuit High Voltage .

	The inspection is complete.