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 (terminal No. 75) 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. 92) or PCM (terminal No. 57) .

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 line.

DESCRIPTIONS OF MONITOR METHODS
- If the heated oxygen sensor (rear) output is higher than the standard value while monitoring the heated oxygen sensor (rear) output, a short circuit (short circuit to power supply) is determined to have occurred.

MONITOR EXECUTION
- Continuous

MONITOR EXECUTION CONDITIONS (Other monitor and Sensor)

Other Monitor (There is no temporary DTC stored in memory for the item monitored)
- Not applicable

Sensor (The sensor is determined to be normal)
- Not applicable

DTC SET CONDITIONS

Logic Flow Chart:

Logic Flowchart

Check Conditions
- 2 seconds or more have passed since the starting sequence was completed.

Judgment Criteria
- Heated oxygen sensor (rear) output voltage has continued to be 1.2 volts or higher for 2 seconds.

OBD-II DRIVE CYCLE PATTERN
Refer to Diagnostic Function - OBD-II Drive Cycle - Procedure 6 - Other Monitor. OBD-II Drive Cycle Pattern Lists

TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
- Heated oxygen sensor (rear) failed.
- Short circuit in heated oxygen sensor (rear) output line.
- 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. Refer to Harness Connector Inspection. 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 (terminal No. 75) 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 - Procedure 6 - Other Monitor. 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.