Troubleshooting

DTC P0156 OXYGEN SENSOR CIRCUIT MALFUNCTION (BANK 2 SENSOR 2)

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 body.

CIRCUIT DESCRIPTION

DTC Detection Condition:

The heated oxygen sensor (HO2S) is used to monitor oxygen in the exhaust gas. For optimum catalyst operation,the air fuel mixture (air-fuel ratio) must be maintained near the ideal stoichiometric ratio. The HO2S output voltage changes suddenly in the vicinity of the stoichiometric ratio. The ECM adjusts the fuel injection time so that the air-fuel ratio is nearly stoichiometric.

The HO2S generates a voltage between 0.1 and 0.9 volts in response to oxygen in the exhaust gas. If the oxygen in the exhaust gas increases, the air-fuel ratio becomes LEAN. The ECM interprets Lean when the HO2S voltage is below 0.45 volts. If the oxygen in the exhaust gas decreases, the air-fuel ratio becomes RICH. The ECM interprets Rich when the HO2S voltage is above 0.45 volts.

MONITOR DESCRIPTION

Monitor Strategy:

Typical Enabling Conditions:

Typical Malfunction Thresholds:

Component Operating Range:

O2S Test Result:

The ECM monitors the rear HO2S by checking to make sure:
- The HO2S voltage does not remain Rich (above 0.5 volts) or Lean (below 0.4 volts) while the vehicle is accelerating and decelerating for 4 to 8 minutes. If the voltage does remain either Rich or Lean, the ECM interprets this as a malfunction, illuminates the Malfunction Indicator Light (MIL) and sets a DTC.
- The HO2S voltage does not remain at less than 0.05 V for a long time while the vehicle is running. If the voltage does remain at less than 0.05 V, the ECM interprets this as a malfunction, illuminates the MIL and sets a DTC.
- The sensor's voltage drops to below 0.2 V (extremely Lean status) immediately when the vehicle decelerates and fuel-cut is operating. If the voltage drops to below 0.2 V, the ECM determine that the sensor's response feature has deteriorated, illuminates the MIL and sets a DTC.

Wiring Diagram:

CONFIRMATION DRIVING PATTERN

Confirmation Driving Pattern:

a. Connect the hand-held tester to the DLC3.
b. Switch from normal mode to check mode.
c. Warm up the engine until the engine coolant temperature reaches to 75 °C (167 °F).
d. Drive the vehicle at 60 km/h (38 mph) for 20 seconds.
e. Allow the engine to idle for 10 seconds.
f. Perform steps (d) to (e) 12 times.

HINT: If a malfunction exists, the Malfunction Indicator Light (MIL) is illuminated 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 the 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 - 6:

INSPECTION PROCEDURE

HINT: Narrowing down the trouble area is possible by performing the A/F CONTROL on the Active Test (HO2S or other trouble areas can be distinguished).

The injection volume can be switched to -12.5 % (decrease) or +25 % (increase) by A/F CONTROL.

The A/F CONTROL procedure enables a technician to check and graph the voltage outputs of the HO2Ss.

A/F CONTROL Procedure:
a. Connect the hand-held tester to the DLC3 on the vehicle.
b. Turn the ignition switch ON.
c. Warm up the engine by running the engine at 2,500 rpm for approximately 90 seconds.
d. Select the item "DIAGNOSIS / ENHANCED OBD II / ACTIVE TEST / A/F CONTROL".
e. Perform A/F CONTROL at the engine idling.

Standard:
The HO2S 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: The front HO2S output has a few seconds of delay and the rear HO2S output has a maximum of 20 seconds of delay.
If the vehicle is short of fuel, the air-fuel ratio becomes LEAN and the DTCs will be recorded.

HINT: Read freeze frame data using the hand-held tester. Freeze frame data records the engine conditions when a malfunction is detected. When troubleshooting, freeze frame data can help determine if the vehicle warunning or stopped, if the engine was warmed up or not, if the air fuel ratio was lean or rich, and other data from the time the malfunction occurred.

CHECK FOR INTERMITTENT PROBLEMS

HINT: Inspect the vehicle's ECM using check mode. Intermittent problems are easier to detect when the hand-held tester is in check mode. In check mode, the hand-held tester uses 1 trip detection logic, which has a higher sensitivity to malfunctions than normal mode (default), which uses 2 trip detection logic.

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.