Troubleshooting
DTC P0156 OXYGEN SENSOR CIRCUIT MALFUNCTION (BANK 2 SENSOR 2)CIRCUIT DESCRIPTION
DTC Detection Condition:
The heated oxygen sensor is used to monitor oxygen concentration in the exhaust. For optimum catalytic converter operation, the air fuel mixture must be maintained near the ideal "stoichiometric" ratio. The oxygen sensor output voltage changes suddenly at the stoichiometric ratio. The ECM adjusts the fuel injection time so that the air-fuel ratio is nearly stoichiometric.
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 (low voltage, i.e. less than 0.45 V).
When the air-fuel ratio is RICHER than the stoichiometric air-fuel ratio, the oxygen will be vanished from the exhaust gas. And the heated oxygen sensor informs the ECM of the RICH condition (high voltage, i.e. more than 0.45 V).
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.
MONITOR DESCRIPTION
Monitor Strategy:
Typical Enabling Conditions:
Typical Malfunction Thresholds:
Component Operating Range:
Monitor Result (Mode 06 Data):
When the sensor output remains RICH or LEAN even though the vehicle has been accelerating and slowing for 5 to 8 minutes, the ECM interprets this as a fault in the rear oxygen sensor. Also, if the rear oxygen sensor output remains at less than 0.05 V for more than 270 seconds (when ECM monitored the oxygen sensor for 300 seconds while the air fuel feed back is being performed), the ECM will interpret this as a fault. In either case, the ECM will turn on the MIL and set a DTC.
Wiring Diagram:
CONFIRMATION DRIVING PATTERN
Confirmation Driving Pattern:
a. Connect the hand-held tester to the DLC3.
b. Switch the hand-held tester from the normal mode to the check (test) mode.
c. Start the engine and let the engine idle for 60 seconds or more.
d. Drive the vehicle at 25 mph (40 km/h) or more for 40 seconds or more.
e. Let the engine idle for 10 seconds or more.
f. Perform steps (d) to (e) 12 times.
HINT: If a malfunction exists, the MIL will be illuminated on the multi-information display during step (f).
NOTE: If the conditions in this test are not strictly followed, detection of a malfunction will not occur. If you do not have a hand-held tester, turn the ignition switch OFF after performing steps from (c) to (f), then perform steps from (c) to (f) 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 the "A/F CONTROL" ACTIVE TEST (A/F sensor, heated oxygen sensor or other trouble areas can be distinguished).
a. Perform ACTIVE TEST using the hand-held tester (A/F CONTROL).
HINT: "A/F CONTROL" is ACTIVE TEST which changes the injection volume -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 by running the engine at 2,500 rpm for approximately 90 seconds.
4. Select the item "DIAGNOSIS/ENHANCED OBD II/ACTIVE TEST/ A/F CONTROL".
5. Perform "A/F CONTROL" with the engine in an 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 seconds delay in the A/F sensor output and there is about 20 seconds delay in the heated oxygen sensor output.
The following A/F CONTROL procedure enables the technician to check and graph the voltage outputs of both the A/F sensor and the 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 related to different systems that have terminal E2 as the ground terminal are output simultaneously, terminal E2 may be open.
- Read freeze frame data using the hand-held tester or the OBD II scan tool. 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.
a. Clear the DTCs.
b. Set the check mode.
c. Perform a simulation test.
d. Check the connector and terminal.
e. Wiggle the harness and the connector.