Troubleshooting
DTC P0156 OXYGEN SENSOR CIRCUIT MALFUNCTION (BANK 2 SENSOR 2)CIRCUIT DESCRIPTION
DTC Detection Condition:
To obtain a high purification rate for the CO, HC and NOx components of the exhaust gas, a three-way catalytic converter is used. For the most efficient use of the three-way catalytic converter, the air-fuel ratio must be precisely controlled so that it is always close to the stoichiometric air-fuel ratio.
The heated oxygen sensor has the characteristic whereby its output voltage changes suddenly in the vicinity of the stoichiometric air-fuel ratio. This is used to detect the oxygen concentration in the exhaust gas and provide the ECM with feedback control the air-fuel ratio.
When the air-fuel ratio becomes LEAN, the oxygen concentration in the exhaust gas increases. And the heated oxygen sensor informs the ECM of the LEAN condition (small electromotive force: < 0.45 V).
When the air-fuel ratio is RICHER than the stoichiometric air-fuel ratio, the oxygen concentration in the exhaust gas is reduced. And the heated oxygen sensor informs the ECM of the RICH condition (large electromotive force: > 0.45 V). The ECM judges by the electromotive force from the heated oxygen sensor whether the air-fuel ratio is RICH or LEAN and controls the injection time accordingly. It the malfunction of the heated oxygen sensor causes an output of abnormal electromotive force, the ECM becomes unable to perform the accurate air-fuel ratio control.
The heated oxygen sensors include a heater which heats the zirconia element. The heater is controlled by the ECM. When the intake air volume is low (the temperature of the exhaust gas is low), current flows to the heater in order to heat the sensor for the accurate oxygen concentration detection.
HINT:
- Bank 1 refers to the bank that includes cylinder No.1.
- Bank 2 refers to the bank that does not include cylinder No.1.
- Sensor 2 refers to the sensor farthest away from the engine assembly.
Wiring Diagram:
CONFIRMATION DRIVING PATTERN
1. Connect the hand-held tester to the DLC3. (*1)
2. Switch the hand-held tester from the normal mode to the check (test) mode. (*1)
3. Start the engine and let the engine idle for 60 seconds or more. (*2)
4. Drive the vehicle at 40 km/h (25 mph) or more for 40 seconds or more. (*3)
5. Let the engine idle for 10 seconds or more. (*4)
6. Perform steps (*3) to (*4) 12 times. (*5)
HINT: If a malfunction exists, the MIL will illuminate on the multi-information display during step (*5).
NOTE: If the conditions in this test are not strictly followed, detection of the malfunction will not be possible. If you do not have a hand-held tester, turn the ignition switch OFF after performing steps from (*2) to (*5), then perform steps from (*2) to (*5) again.
Step 1 - 2:
Step 3 - 4:
Step 5:
Step 6 - 7:
INSPECTION PROCEDURE
HINT:
Hand-held tester only:
Narrowing down the trouble area is possible by performing ACTIVE TEST of the following "A/F CONTROL" (A/F sensor, heated oxygen sensor or other trouble areas can be distinguished).
a. Perform ACTIVE TEST by the hand-held tester (A/F CONTROL).
HINT: "A/F CONTROL" is ACTIVE TEST which changes the injection volume to -12.5 % or +25 %.
1. Connect the hand-held tester to the DLC3 on the vehicle.
2. Turn the ignition switch ON.
3. Warm up the engine with the engine speed at 2,500 rpm for approx. 90 sec.
4. Select the item "DIAGNOSIS/ENHANCED OBD II/ACTIVE TEST/ A/F CONTROL".
5. Perform "A/F CONTROL" when idle condition (press the right or left button).
Result:
A/F sensor reacts in accordance with increase and decrease of injection volume:
+25 % -> rich output: Less than 3.0 V
-12.5 % -> lean output: More than 3.35 V
Heated oxygen sensor reacts in accordance with increase and decrease of injection volume:
+25 % -> rich output: More than 0.55 V
-12.5 % -> lean output: Less than 0.4 V
NOTE: There is a few second delay in the A/F sensor output and there is about 20 seconds delay in the heated oxygen sensor output.
The following procedure of A/F CONTROL enables the user to check its output (show its graph indication) of A/F sensor and heated oxygen sensor.
For displaying the graph indication, enter "ACTIVE TEST/ A/F CONTROL/USER DATA", then select "AFS B1S1 and O2S B1S2" or "AFS B2S1 and O2S B2S2" by pressing "YES" button and push "ENTER" button before pressing "F4" button.
HINT:
- If different DTCs that are related to a different system are output simultaneously while terminal E2 is used as a ground terminal, terminal E2 may be open.
- Read freeze frame data using the hand-held tester or the OBD II scan tool, as freeze frame data records the engine conditions when a malfunction is detected. When troubleshooting, it is useful for determining whether the vehicle was running or stopped, the engine was warmed up or not, the air-fuel ratio was lean or rich, etc. at the time of the malfunction.
CHECK FOR INTERMITTENT PROBLEMS
Hand-held tester only:
By putting the vehicle's ECM in the check mode, the 1 trip detection logic is possible instead of the 2 trip detection logic, and the sensitivity to detect faults is increased. This makes it easier to detect intermittent problems.
1. Clear the DTCs.
2. Set the check mode.
3. Perform a simulation test.
4. Check the connector and terminal.
5. Wiggle the harness and the connector.