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DTC P0138: Heated Oxygen Sensor (rear) Circuit High Voltage
 
 
 
 
CIRCUIT OPERATION
  • A voltage corresponding to the oxygen concentration in the exhaust gas is sent to the ECM terminal O2RL from the output terminal of the heated oxygen sensor (rear).
  • Terminal ORLE of the heated oxygen sensor (rear) is grounded with ECM terminal ORLE.
  • The ECM applies an offset voltage of 0.5 volt to ground terminal of the heated oxygen sensor (rear).
 
 
TECHNICAL DESCRIPTION
  • The output signal of the linear air-fuel ratio sensor 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
  • Heated oxygen sensor (rear) output voltage is over specified range.
 
 
MONITOR EXECUTION
  • Continuous
 
 
MONITOR EXECUTION CONDITIONS (Other monitor and Sensor)
Other Monitor (There is no temporary DTC set in memory for the item monitored below)
  • Linear air-fuel ratio sensor monitor
  • Linear air-fuel ratio sensor heater monitor
  • Heated oxygen sensor (rear) heater monitor
  • Heated oxygen sensor offset voltage monitor
Sensor (The sensor below is determined to be normal)
  • Mass airflow sensor
  • Engine coolant temperature sensor
  • Intake air temperature sensor
  • Barometric pressure sensor
  • Fuel tank pressure sensor
 
 
DTC SET CONDITIONS
Logic Flow Chart
 
 
Check Conditions
  • More than 2 seconds have passed since the power supply mode of the electric motor switch was ON.
  • Heated oxygen sensor offset voltage is between 0.4 and 0.6 volt.
Judgment Criterion
  • Heated oxygen sensor (rear) output voltage has continued to be higher than 1.8 volts for 2 seconds.
 
 
FAIL-SAFE AND BACKUP FUNCTION
  • None.
 
 
OBD-II DRIVE CYCLE PATTERN
  • Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 2 .
 
 
TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
  • Shorted heated oxygen sensor (rear) circuit or connector damage.
  • ECM failed.

 
 
DIAGNOSIS
STEP 1. Using scan tool (M.U.T.-IIISE), check data list item AD: Heated Oxygen Sensor (rear).
cautionTo prevent damage to scan tool (M.U.T.-IIISE), always turn off the power supply mode of the electric motor switch before connecting or disconnecting scan tool (M.U.T.-IIISE).
(1) Connect scan tool (M.U.T.-IIISE). Refer to HOW TO CONNECT THE SCAN TOOL (M.U.T.-IIISE) .
(2) Set the vehicle to the continuous idling mode.
(3) Set scan tool (M.U.T.-IIISE) to the data reading mode for item AD, Heated Oxygen Sensor (rear).
  • The output voltages should be between 0.6 and 1.0 volt.
(4) Turn off the power supply mode of the electric motor switch.
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 .
Go to Step 2.
 
STEP 2. Check of short circuit to power supply in O2RL line between heated oxygen sensor (rear) connector and ECM connector.
Is the harness wire in good condition?
Go to Step 3.
Repair the connector(s) or wiring harness. Then go to Step 4.
 
STEP 3. Using scan tool (M.U.T.-IIISE), check data list item AD: Heated Oxygen Sensor (rear).
(1) Set the vehicle to the continuous idling mode.
(2) Set scan tool (M.U.T.-IIISE) to the data reading mode for item AD, Heated Oxygen Sensor (rear).
  1. The output voltages should be between 0.6 and 1.0 volt.
(3) Turn off the power supply mode of the electric motor switch.
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 ECM (Refer to Removal and Installation ). Then go to Step 4.
 
STEP 4. 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 2 .
(2) Check the diagnostic trouble code (DTC).
Is DTC P0138 set?
Retry the troubleshooting.
The inspection is complete.