P0138

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 No. 40) from the output terminal (terminal No.
3) of the heated oxygen sensor (rear).

- Terminal No. 4 of the heated oxygen sensor (rear) is grounded with ECM (terminal No. 41).

- The ECM applies an offset voltage of 0.5 volt to terminal No. 4 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 stored 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

DTC SET CONDITIONS

Logic Flow Chart






Check Conditions

- Heated oxygen sensor offset voltage is between 0.4 and 0.6 volt.

- 2 seconds or more have passed since the engine starting sequence was completed.
Judgement 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 23 OBD- II Drive Cycle.

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. Check harness connector D-37 at heated oxygen sensor
(rear) and harness connector B-10 at ECM for damage.

Q. Is the harness connector in good condition?

YES Go to Step 2.
NO Repair or replace it. Harness Connector Inspection.
Then go to Step 3.
STEP 2. Check for short circuit to power supply between heated oxygen sensor (rear) connector D-37 (terminal No. 3) and ECM connector B-10 (terminal No. 40).

NOTE:
Check harness after checking intermediate connector A-13 and C-129. If intermediate connector is damaged, repair or replace it. Harness Connector Inspection.
Then go to Step 3.

Q. Is the harness wire in good condition?

YES Replace the ECM. When the ECM is replaced, register the ID code. Refer to ID registration procedure manual - ID codes registration judgement table [Vehicles with KOS] or ID registration procedure manual - ID codes registration judgement table [Vehicles with WCM]. 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 23 OBD- II Drive Cycle.

(2)Check the diagnostic trouble code (DTC).

Q. Is DTC P0138 set?

YES Retry the troubleshooting.
NO The inspection is complete.