P0139
CIRCUIT OPERATION
- A voltage corresponding to the oxygen concentration in the exhaust gas is sent to the ECM (terminal 75)
- Terminal 4 of the heated oxygen sensor (rear) is grounded with ECM (terminal 92)
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
DTC SET CONDITIONS
Check Conditions
- Engine coolant temperature is higher than 82 °C (180 °F).
- Barometric pressure is higher than 76 kPa (11 psi).
- The heated oxygen sensor (front) is active.
Judgement Criteria
- The heated oxygen sensor (rear) output voltage, before the fuel shut off is started, was 0.4 volts or more, and during the shut off, it takes one second or more for the heated oxygen sensor (rear) output voltage to fall from 0.4 to 0.15 volts.
or
- The heated oxygen sensor (rear) output voltage, before the fuel shut off is started, was 0.15 volts or more, and during the shut off, it takes three seconds or more for the heated oxygen sensor (rear) output voltage to fall below 0.15 volts.
TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
- Heated oxygen sensor (rear) failed.
- Open circuit in heated oxygen sensor (rear) output line.
- Open circuit in heated oxygen sensor (rear) ground line.
- ECM failed.
- PCM failed.
DIAGNOSIS
Required Special Tools
MB991502: Scan Tool (MUT-II)
STEP 1. Using scan tool MB991502, check data list item 59: Heated Oxygen Sensor (rear).
CAUTION: To prevent damage to scan tool MB991502, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991502.
1. Connect scan tool MB991502 to the data link connector.
2. Start the engine and run at idle.
3. Set scan tool MB991502 to the data reading mode for item 59, Heated Oxygen Sensor (rear).
4. Warm up the engine.
- After increasing the output voltage 0.15 volts or more by the engine revving, finish it. Then confirm that the output voltage reduces to 0.15 volts or less within 3 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. Refer to How to Use Troubleshooting/Inspection Service Points.
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 Procedure 6 - Other Monitor.
2. Check the diagnostic trouble code (DTC).
Q: Is the DTC P0139 is output?
YES: Retry the troubleshooting.
NO: The inspection is complete.