P0137

DTC P0137: Heated Oxygen Sensor Circuit Low Voltage

Heated Oxygen Sensor (Rear) Circuit:

CIRCUIT OPERATION
- A voltage corresponding to the oxygen concentration in the exhaust gas is sent to the ECM (terminal No.73) from the output terminal (terminal No.4) of the heated oxygen sensor (rear).
- Terminal No.2 of the heated oxygen sensor (rear) is grounded with ECM (terminal No.49).

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 stays low when air/fuel ratio is forced to be rich. The above procedure is repeated when oxygen sensor is inactive.

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
- After 2 seconds or more pass from the time when the monitor determines normally for detecting an open circuit.
- Heated oxygen sensor (rear) signal voltage has continued to be 0.15 volt or lower.
- Engine coolant temperature is higher than 76 degrees C (169 degrees F).
- Volume airflow sensor output frequency is 56 Hz or more.
- At least 20 seconds have passed since fuel shut off control was canceled.
- Monitoring time: 8 seconds.

Judgment Criterion
- Making the air/fuel ratio 15 percent for 8 seconds richer does not result in raising the heated oxygen sensor (rear) output voltage beyond 0.15 volt.

OBD-II DRIVE CYCLE PATTERN
Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 11. 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 (M.U.T.-III Sub Assembly)
- MB991824: V.C.I.
- MB991827: USB Cable
- MB991911: Main Harness B
- MB991658: Test Harness Set

STEP 1. Using scan tool MB991958, check data list item 59: Heated Oxygen Sensor (rear).

CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.




1. Connect scan tool MB991958 to the data link connector.
2. Start the engine and run at idle.
3. Set scan tool MB991958 to the data reading mode for item 59, Heated Oxygen Sensor (rear).
a. Transaxle: 2nd speed
b. Drive with wide open throttle
c. Engine: 3,500 r/min or more
- The output voltage should be between 0.6 and 1.0 volt.

4. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is the sensor operating properly?

YES: It can be assumed that this malfunction is intermittent.

NO: Go to Step 2.

STEP 2. Check the heated oxygen sensor (rear).




1. Disconnect the heated oxygen sensor (rear) connector D-40 and connect test harness special tool, MB991658, to the connector on the heated oxygen sensor (rear) side.
2. Warm up the engine until engine coolant temperature reaches 80 degrees C (176 degrees F) or higher.
3. Drive at 50 km/h (31 mph) or more for 10 minutes.




4. Connect a digital voltage meter between terminal No.2 and terminal No.4.
5. Measure the output voltage of the heated oxygen sensor under the following driving.
- Transaxle: 2nd speed
- Drive with wide open throttle
- Engine: 3,500 r/min or more

Standard value: 0.6 - 1.0 volt

NOTE: If the sufficiently high temperature [of approximate 400 degrees C (752 degrees F) or more] is not reached although the heated oxygen sensor is normal, the output voltage would be possibly low although the rich air/fuel ratio.

Q: Is the measured voltage between 0.6 and 1.0 volt?

YES: Go to Step 3.

NO: Replace the heated oxygen sensor (rear). Then go to Step 5.







STEP 3. Check harness connector D-40 at heated oxygen sensor (rear) and connector C-117 at ECM for damage.

Q: Is the harness connector in good condition?

YES: Go to Step 4.

NO: Repair or replace it. Then go to Step 5.







STEP 4. Check for short circuit to ground between heated oxygen sensor (rear) connector D-40 (terminal No.4) and ECM connector C-117 (terminal No.73).

Q: Is the harness wire in good condition?

YES: Replace the ECM. Then go to Step 5.

NO: Repair it. Then go to Step 5.

STEP 5. 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 11. OBD-II Drive Cycle Pattern Lists
2. Check the diagnostic trouble code (DTC).

Q: Is DTC P0137 set?

YES: Retry the troubleshooting.

NO: The inspection is complete.