P0138

DTC P0138: Heated Oxygen Sensor Circuit High Voltage

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) from the output terminal (terminal No. 1) of the heated oxygen sensor (rear).
- Terminal 2 of the heated oxygen sensor (rear) is grounded with ECM (terminal No. 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 checks for an open circuit in the heated oxygen sensor (rear) output line.

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 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.
- Connector damage.
- ECM failed.

DIAGNOSIS

Required Special Tools:
- MB991958: Scan Tool (MUT-III Sub Assembly)
- MB991824: V.C.I.
- MB991827: USB Cable
- MB991911: Main Harness B







STEP 1. Check harness connector D-40 at heated oxygen sensor (rear) and harness connector C-115 at ECM 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 D-40 (terminal No. 1) and ECM connector C-115 (terminal No. 75).

Q: Is the harness wire in good condition?

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

NO: Repair it. Then go to Step 3.

STEP 3. Perform 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: Repeat the troubleshooting.

NO: The procedure is complete.