DTC P0139: Heated Oxygen Sensor Circuit Slow Response (sensor 2)

CIRCUIT OPERATION
• A voltage corresponding to the oxygen concentration in the exhaust gas is sent to the ECM (terminal No. 75) <M/T> or PCM (terminal No. 73) <A/T> from the output terminal (terminal No. 1) of the heated oxygen sensor (rear).
• Terminal No. 2 of the heated oxygen sensor (rear) is grounded with ECM (terminal No. 92) <M/T> or PCM (terminal No. 57) <A/T>.
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 <M/T> or PCM <A/T> checks for an open circuit in the heated oxygen sensor (rear) output line.
DESCRIPTIONS OF MONITOR METHODS
• If the heated oxygen sensor (rear) output does not change in spite of repeating the prescribed (stop-and-go) driving pattern that includes a fuel shut-off, the heated oxygen sensor (rear) is determined to be stuck with faulty output.
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) heater monitor
• Heated oxygen sensor (rear) heater monitor
• Air/fuel ratio feedback system monitor

Sensor (The sensor below is determined to be normal)
• Volume airflow sensor
• Barometric pressure sensor
• Intake air temperature sensor
• Engine coolant temperature sensor
DTC SET CONDITIONS Logic Flow Chart


Check Conditions
• Engine coolant temperature is higher than 76°C (169°F).
• The heated oxygen sensor (front) is active.
• The cumulative volume airflow sensor output frequency is higher than 4,000 Hz.
• Repeat 3 or more times: drive*1, stop*2.
Drive*1:
• Engine speed is higher than 1,500 r/min.
• Volumetric efficiency is higher than 40 percent.
• Vehicle speed is higher than 30 km/h (18.7 mph).
• A total of more than 10 seconds have elapsed with the above mentioned conditions, and more than 2 seconds have elapsed with the fuel shut off.
Stop*2:
• Vehicle speed is lower than 1.5 km/h (0.9 mph).

Judgement Criterion
• Change in the output voltage of the heated oxygen sensor (rear) is lower than 0.313 volt.
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 12 .
TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:
• Heated oxygen sensor (rear) failed.
• ECM failed. <M/T>
• PCM failed. <A/T>