P0138

DTC P0138: Heated Oxygen Sensor Circuit High Voltage (sensor 2)

Heated Oxygen Sensor (rear) Circuit Part 1:

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 PCM (terminal No. 73) 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. 75) or PCM (terminal No. 63) .
- The ECM or the PCM applies an offset voltage of 0.5 volt to terminal No. 2 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 or PCM checks for an open circuit in 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 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)
- Volume airflow sensor
- Engine coolant temperature sensor
- Intake air temperature sensor
- Barometric pressure sensor

DTC SET CONDITIONS

Logic Flow Chart:

Logic Flow Chart

Check Condition
- 2 seconds or more have passed since the starting sequence was completed.
- 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 1.8 volts or higher for 2 seconds.

OBD-II DRIVE CYCLE PATTERN
Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 21 OBD-II Drive Cycle Pattern Lists.

TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
- Short circuit in heated oxygen sensor (rear) output line.
- Connector damage.
- ECM failed.
- PCM failed.

DIAGNOSIS

STEP 1. Check harness connector C-11 at heated oxygen sensor (rear) and harness connector C-115 at ECM or harness connector C-116 at PCM for damage.

Q: Is the harness connector in good condition?

YES: Go to Step 2.

NO: Repair or replace it. Then go to Step 3.

STEP 2. Check for short circuit to power supply between heated oxygen sensor (rear) connector C-11 (terminal No. 1) and ECM connector C-115 or PCM connector C- 116 (terminal No. 73).

Q: Is the harness wire in good condition?

YES: Replace the ECM or PCM. Then go to Step 3.

NO: Repair it. Then go to Step 3.

STEP 3. 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 21 OBD-II Drive Cycle Pattern Lists.
2. Check the diagnostic trouble code (DTC).

Q: Is DTC P0138 set?

YES: Retry the troubleshooting.

NO: The inspection is complete.