P0138
DTC P0138 HEATED OXYGEN SENSOR CIRCUIT HIGH VOLTAGE (BANK 1 SENSOR 2)CIRCUIT DESCRIPTION
DTC Detection Condition:
The heated oxygen sensor is used to monitor oxygen concentration in the exhaust gas. For optimum catalytic converter operation, the air fuel mixture must be maintained near the ideal stoichiometric ratio. The heated oxygen sensor 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.
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).
MONITOR DESCRIPTION
Monitor Strategy:
Typical Enabling Conditions:
Typical Malfunction Thresholds:
Component Operating Range:
O2S Test Result (Mode 05 Data):
The ECM monitors the rear heated oxygen sensor in the following 3 items:
1. If the rear heated oxygen sensor voltage changes between RICH and LEAN while the vehicle is running (repeating acceleration and deceleration), the ECM interprets this as a malfunction and illuminates the MIL, and then sets a DTC.
2. If the rear heated oxygen sensor voltage does not remain less than 0.05 V for a long period of time while the vehicle is running, the ECM interprets this as a malfunction and illuminates the MIL, and then sets a DTC.
3. If the sensor's voltage drops below 0.2 V (extremely LEAN status) immediately when the vehicle decelerates and the fuel cut is working. If not, the ECM interprets this as a sensor's response feature deterioration and illuminates the MIL, and then sets DTC.
Wiring Diagram:
CONFIRMATION DRIVING PATTERN
CAUTION: Strictly observe posted speed limits, traffic laws, and road conditions when conducting the drive pattern.
a. Connect the hand-held tester to the DLC3.
b. Turn the ignition switch to ON.
c. Turn the tester ON.
d. Clear DTCs.
e. Run the engine at idle for 2 minutes.
f. Warm up the engine until the engine coolant temperature (ECT) reaches 75 °C (167 °F).
g. Allow the vehicle to run at 30 mph (48 km/h) or more for 40 seconds or more.
h. Stop the vehicle and run the engine at idle for 20 seconds or more.
i. Repeat the steps (g) and (h) at least 8 times in one driving cycle.
j. Move the shift lever into the second gear.
k. Depress the accelerator pedal for at least 10 seconds.
l. Allow the vehicle to run at 30 mph (48 km/h) or more.
m. Immediately after step (l), release the accelerator pedal for at least 10 seconds without depressing the brake pedal (to execute fuel-cut).
n. Decelerate the vehicle until the vehicle speed drops less than 6 mph (10 km/h).
o. Repeat the steps (k), (l), (m) and (n) at least twice in one driving cycle.
HINT: The HO2 sensor operates when the following conditions are met:
- 2 minutes or more passed after the engine start.
- The ECT is 75 °C (167 °F) or more.
- Cumulative running time at 30 mph (48 km/h) or more exceeds 6 minutes.
- Closed loop.
- Fuel-cut is operated for 8 seconds or more.
Step 1 - 4:
Step 5 - 7:
INSPECTION PROCEDURE
HINT:
Hand-held tester only:
Malfunctioning areas can be found by performing the ACTIVE TEST / A/F CONTROL operation (Heated Oxygen [HO2] sensor or other trouble areas). The A/F CONTROL operation can determine whether the front HO2 sensor (sensor1), rear HO2 sensor (sensor 2) and other potential trouble areas are malfunctioning or not.
a. Perform A/F CONTROL using the hand-held tester.
HINT: The A/F Control operation lowers the fuel injection volume by 12.5 % or increases the injection volume by 25 %.
1. Connect the hand-held tester to the DLC3.
2. Turn the ignition switch to ON and turn the hand-held tester ON.
3. Warm up the engine by running the engine at 2,500 rpm for approximately 90 seconds.
4. On the hand-held tester, select the following menu items: DIAGNOSIS / ENHANCED OBD II / ACTIVE TEST / A/F CONTROL.
5. Perform the A/F CONTROL operation with the engine idling (press the right or left button).
Result:
The heated oxygen sensor reacts in accordance with increase and decrease of the fuel injection volume.
+25 % -> Rich output: More than 0.5 V
-12.5 % -> Lean output: Less than 0.4 V
NOTE: The front heated oxygen sensor has an output delay of a few seconds and the rear heated oxygen sensor has a maximum output delay of approximately 20 seconds.
The following A/F CONTROL procedure enables the technician to check the graph of the voltage outputs of both front and rear heated oxygen sensors.
To display the graph, enter ACTIVE TEST/ A/F CONTROL / USER DATA, select "O2S B1S1 and O2S B1S2" by pressing the "YES" button and then the "ENTER". Then press the "F4" button.
NOTE: If the vehicle is short of fuel, the air-fuel ratio becomes LEAN and heated oxygen sensor DTCs are set, and the MIL then comes on.
HINT:
- If different DTCs related to different systems that have terminal E2 as the ground terminal are output simultaneously, terminal E2 may have an open circuit.
- Read freeze frame data using the hand-held tester. Freeze frame data records the engine conditions when malfunctions are detected. When troubleshooting, freeze frame data can help determine if the vehicle was moving or stationary, 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.
- If the OX1B wire from the ECM connector is short-circuited to the +B wire, DTC P0136 is set.
CHECK FOR INTERMITTENT PROBLEMS
Hand-held tester only:
Inspect the vehicle's ECM using check mode. Intermittent problems are easier to detect when the ECM is in check mode with hand-held tester. In check mode, the ECM 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 connector.