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 heated oxygen sensor (front) 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

MONITOR EXECUTION

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 (front) monitor
Heated oxygen sensor heater (front) monitor
Heated oxygen sensor heater (rear) monitor
Heated oxygen sensor inactive (front) monitor
Heated oxygen sensor offset voltage monitor
Air/fuel ratio feedback 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

2 seconds or more have passed since the engine starting sequence was completed.
Heated oxygen sensor offset voltage is between 0.4 and 0.6 volt.

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

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.

DIAGNOSIS

STEP 1. Check harness connector D-40 at heated oxygen sensor (rear) and harness connector B-108 at ECM for damage.

Q. Is the harness connector in good condition?

	Go to Step 2.

	Repair or replace it. Refer to GROUP 00E, 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. 3) and ECM connector B-108 (terminal No. 40).

note

Check harness after checking intermediate connector A-10 and C-37. If intermediate connector is damaged, repair or replace it. Refer to GROUP 00E, Harness Connector Inspection

. Then go to Step 3.

Q. Is the harness wire in good condition?

	Replace the ECM. When the ECM is replaced, register the ID code. Refer to GROUP 42B, Diagnosis - ID Code Registration Judgment Table <Vehicles with KOS> or GROUP 42C, Diagnosis - ID Codes Registration Judgment Table <Vehicles with WCM> . Then go to Step 3.

	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

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

Q. Is DTC P0138 set?

	Retry the troubleshooting.

	The inspection is complete.