P0157

DTC P0157: Heated Oxygen Sensor Circuit Low Voltage (bank 2, sensor 2)

Left Bank Heated Oxygen Sensor (Rear) Circuit Part 1:

Left Bank Heated Oxygen Sensor (Rear) Circuit Part 2:

CIRCUIT OPERATION
- A voltage corresponding to the oxygen concentration in the exhaust gas is sent to the PCM (terminal No. 96) from the output terminal (terminal No. 4) of the left bank heated oxygen sensor (rear).
- Terminal No. 2 of the left bank heated oxygen sensor (rear) is grounded with PCM (terminal No. 69).

TECHNICAL DESCRIPTION
- The output signal of the left bank heated oxygen sensor (front) is compensated by the output signal of the left bank heated oxygen sensor (rear).
- The PCM checks for an open circuit in the left bank heated oxygen sensor (rear) output line.

DESCRIPTIONS OF MONITOR METHODS
Left bank 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)
- Mass airflow sensor.
- Engine coolant temperature sensor.
- Intake air temperature sensor.
- Barometric pressure sensor.

DTC SET CONDITIONS

Logic Flow Chart:

Logic Flow Chart

Check Conditions
- 3 minutes or more have passed since the engine starting sequence was completed.
- Left bank heated oxygen sensor (rear) signal voltage has continued to be 0.15 volt or lower.
- Engine coolant temperature is higher than 76 °C (169 °F)
- Engine speed is higher than 1,200 r/min
- Volumetric efficiency is higher than 25 percent
- Mass airflow sensor output is 8 g/sec or more.
- At least 20 seconds have passed since fuel shut off control was canceled.
- Monitoring time: 10 seconds

Judgement Criteria
- Making the air/fuel ratio 15 percent for 10 seconds richer does not result in raising the left bank heated oxygen sensor (rear) output voltage beyond 0.15 volt

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:)
- Left bank heated oxygen sensor (rear) failed.
- Short circuit in left bank heated oxygen sensor (rear) output line.
- Connector damage.
- PCM failed.

DIAGNOSIS

Required Special Tools:
- MB991958: Scan Tool (MUT-III Sub Assembly)
- MB991824: V.C.I
- MB991827: USB Cable
- MB991910: Main Harness A

- MB991316: Test Harness




STEP 1. Using scan tool MB991958, check data list item 59: Heated Oxygen Sensor Bank 2, Sensor 2 (left bank)

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 Bank 2, Sensor 2 (left rear).
- Warming up the engine When the engine is revved, the output voltage should repeat 0 volt and 0.6 to 1.0 volt alternately.

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. Refer to How to Use Troubleshooting/Inspection Service Points.

NO: Go to Step 2







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

1. Disconnect the left bank heated oxygen sensor (rear) connector B-24 and connect test harness special tool, MB991316, to the connector on the left bank heated oxygen sensor (front) side
2. Warm up the engine until engine coolant temperature reaches 80 °C (176 °F) or higher
3. Perform a tracing for 5 minutes or more with the engine speed of 4,500 r/min
4. Connect a digital volt meter between terminal No. 2 (black clip) and terminal No. 4 (white clip)
5. While repeatedly revving the engine, measure the heated oxygen sensor (rear) output voltage

Standard value: 0.6 - 1.0 volt

CAUTION:
- Be very careful when connecting the jumper wire; incorrect connection can damage the oxygen sensor.
- Be careful the heater is broken when voltage of beyond 8 V is applied to the oxygen sensor heater.

NOTE: If the sufficiently high temperature (of approximate 400 °C or more) is not reached although the oxygen sensor is normal, the output voltage would be possibly low although the rich air-fuel ratio. Therefore, if the output voltage is low, use a jumper wire to connect the terminal No. 1 (red clip of special tool) and the terminal No. 3 (blue clip of special tool) of the oxygen sensor with a (+) terminal and (-) terminal of 8 V power supply respectively, then check again.

Q: Is the voltage between 0.6 and 1.0 volt?

YES: Go to Step 3.

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







STEP 3. Check harness connector B-24 at left bank heated oxygen sensor (rear) and harness connector B-22 at PCM for damage.

Q: Is the harness connector in good condition?

YES: Go to Step 4.

NO: Repair or replace it. Refer to Harness Connector Inspection. Then go to Step 5.







STEP 4. Check for short circuit to ground between left bank heated oxygen sensor (rear) connector B-24 (terminal No. 4) and PCM connector B-22 (terminal No. 96).

Q: Is the harness wire in good condition?

YES: Replace the PCM. 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 - Procedure 6 - Other Monitor. OBD-II Drive Cycle Pattern Lists
2. Check the diagnostic trouble code (DTC).

Q: Is DTC P0157 set?

YES: Retry the troubleshooting.

NO: The inspection is complete.