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P0156

Left Bank Heated Oxygen Sensor (rear) Circuit:




Connectors:




CIRCUIT OPERATION
- A voltage corresponding to the oxygen concentration in the exhaust gas is sent to the PCM (terminal 73) from the output terminal (terminal 4) of the left bank heated oxygen sensor (rear).
- Terminal 2 of the left bank heated oxygen sensor (rear) is grounded with PCM (terminal 57).

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.

DTC SET CONDITIONS

Check Area
- Left bank heated oxygen sensor (rear) signal voltage has continued to be 0.15 volt or lower for three minutes or more after the starting sequence was completed.
- Engine coolant temperature is higher than approximately 82° C (180° F).
- Engine speed is higher than 1,200 r/min.
- Volumetric efficiency is higher than 25 percent.
- Monitoring time: 7 seconds.

Judgment Criteria
- Input voltage supplied to the PCM interface circuit is higher than 4.5 volts when 5 volts is applied to the left bank heated oxygen sensor (rear) output line via a resistor.
- Only one monitor during one drive cycle.

Check Area
- Left bank heated oxygen sensor (rear) signal voltage remains 0.15 volt or less for at least three minutes after the engine is started.
- Engine coolant temperature is higher than approximately 82° C (180° F).
- Engine speed is higher than 1,200 r/min.
- Volumetric efficiency is higher than 25 percent.
- Volume air flow sensor output frequency is 100 Hz or more.
- At least twenty seconds have passed since fuel shut off control was canceled.
- The left bank heated oxygen sensor outputs 0.5 volts or more.
- Monitoring time: 10 seconds.

Judgment 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.
- Only one monitor during one drive cycle.

Check Area
- Engine coolant temperature is higher than approximately 82° C (180° F).
- Barometric pressure is higher than 76 kPa (11 psi).
- The left bank heated oxygen sensor (front) is active.

Judgment Criteria
- The left bank heated oxygen sensor (rear) output voltage, before the fuel shut off is started, was 0.4 volts or more, and during the shut off, it takes one second or more for the left bank heated oxygen sensor (rear) output voltage to fall from 0.4 to 0.15 volts.
or
- The left bank heated oxygen sensor (rear) output voltage, before the fuel shut off is started, was 0.15 volts or more, and during the shut off, it takes three seconds or more for the left bank heated oxygen sensor (rear) output voltage to fall below 0.15 volts.

TROUBLESHOOTING HINTS
The most likely causes for this code to be set are:
- Left bank heated oxygen sensor (rear) failed.
- Open circuit in left bank heated oxygen sensor (rear) output line.
- Open circuit in left bank heated oxygen sensor (rear) ground line.
- PCM failed.

DIAGNOSIS
Required Special Tool:
MB991502: Scan Tool (MUT-II)

CAUTION: To prevent damage to the scan tool, turn the ignition switch "OFF" before connecting or disconnecting the scan tool.




STEP 1. Using scan tool MB991502, check data list item 69: Heated Oxygen Sensor (rear).
- The output voltage should be 0.6 volt or more when accelerated with a wide open throttle.

If not within specifications, go to Step 2.

If within specifications, it can be assumed that this malfunction is intermittent







STEP 2. Check the harness wire between the left bank heated oxygen sensor (rear) connector E-48 and the PCM connectors C-90, C-91.

NOTE: After inspecting the intermediate connectors C-71, C-79 and E-45, inspect the wire. If the intermediate connectors C-71, C-79 and E-45 are damaged, repair or replace them. Refer to vehicle level Testing and Inspection. Then go to Step 5.

If the wire between the left bank heated oxygen sensor (rear) connector E-48 and the PCM connectors C-90, C-91 are not damaged, go to Step 3.

If the wire between the left bank heated oxygen sensor (rear) connector E-48 and the PCM connectors C-90, C-91 are damaged, repair it. Then go to Step 5.







STEP 3. Check for damage of the harness connector E-48 at the left bank heated oxygen sensor (rear) and the harness connectors C-90, C-91 at the PCM.

If the harness connector E-48 and the harness connectors C-90, C-91 are in good condition, go to Step 4.

If the harness connector E-48 and the harness connectors C-90, C-91 are damaged, repair or replace them. Refer to vehicle level Testing and Inspection. Then go to Step 5.

STEP 4. Replace the left bank heated oxygen sensor (rear).
1. Replace the left bank heated oxygen sensor (rear).
2. Carry out a test drive with the drive cycle pattern. Refer to Procedure 4 - Heated Oxygen Sensor Monitor and Procedure 6 - Other Monitor.
3. Read in the diagnostic trouble code (DTC).

If DTC P0156 is output, replace the PCM. Then go to Step 5.

If DTC P0156 is not output, the inspection is complete.

STEP 5. Test the OBD-II drive cycle.
1. Carry out a test drive with the drive cycle pattern. Refer to Procedure 4 - Heated Oxygen Sensor Monitor and Procedure 6 - Other Monitor.

2. Read the diagnostic trouble code, and confirm that a diagnostic trouble code is not being output.


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