P0138
DTC P0138 OXYGEN SENSOR CIRCUIT HIGH VOLTAGE (BANK 1 SENSOR 2)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 V 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 the air-fuel ratio as Lean when the HO2S voltage is below 0.45 V. If the oxygen in the exhaust gas decreases, the air-fuel ratio becomes Rich. The ECM interprets the air-fuel ratio as Rich when the HO2S voltage is above 0.45 V.
MONITOR DESCRIPTION
Monitor Strategy:
Typical Enabling Conditions Part 1:
Typical Enabling Conditions Part 2:
Typical Malfunction Thresholds Part 1:
Typical Malfunction Thresholds Part 2:
Component Operating Range:
O2S Test Result:
The heated oxygen sensor (HO2S) outputs a voltage of 0 to 1 V. The voltage varies with oxygen density in the exhaust gas. The ECM measures the voltage to monitor the HO2S.
Voltage
The ECM counts the time while the HO2S voltage is lower than 0.05 V. When the time exceeds a malfunction threshold, the ECM illuminates the MIL and sets DTC P0136 or P0156 (2-trip detection logic).
Switching
The ECM counts the frequency of the HO2S switching. When the HO2S does not switch for a certain period, the ECM illuminates the MIL and sets DTC P0136 or P0156 (2-trip detection logic).
Low voltage
The ECM measures the HO2S voltage. When the voltage is lower than 0.03 V for 90 seconds, the ECM illuminates the MIL and sets DTC P0137 or P0157.
Voltage during fuel-cut
The ECM measures the HO2S voltage during the fuel-cut. When the voltage does not reach 0.2 V during the fuel-cut, the ECM illuminates the MIL and sets DTC P0138 or P0158 (2-trip detection logic).
High voltage
The ECM measures the HO2S voltage. When the voltage is higher than 1.2 V for 10 seconds, the ECM illuminates the MIL and sets DTC P0138 or P0158.
CONFIRMATION DRIVING PATTERN (P0136 and/or P0156)
a. Connect the hand-held tester to the DLC3.
b. Switch the hand-held tester from normal mode to check (test) mode.
c. Start the engine and warm it up until the engine coolant temperature becomes more than 75 °C.
d. Drive the vehicle at 60 km/h (38 mph) or more for 40 seconds or more.
e. Run the engine at idle for 10 seconds or more.
f. Perform steps (d) to (e) 12 times.
HINT: If a malfunction exists, the MIL will illuminate during step (f).
NOTE: If the conditions in this test are not strictly followed, a malfunction will not be detected. 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.
CONFIRMATION DRIVING PATTERN (P0137 and/or P0157)
Warm up the engine and run the engine at 60 km/h (38 mph) for 7 minutes.
CONFIRMATION DRIVING PATTERN (P0138 and/or P0158)
Warm up the engine and run the engine at idle for 30 seconds.
Wiring Diagram:
Step 1 - 3:
Step 4 - 6:
Step 7 - 8:
Step 9:
Step 10 - 14:
Step 15:
INSPECTION PROCEDURE
HINT:
Hand-held tester only:
The malfunctioning area can be found by the ACTIVE TEST A/F CONTROL operation. The A/F CONTROL operation can determine if the A/F sensor, heated oxygen sensor or other suspected areas are malfunctioning or not.
Perform the ACTIVE TEST A/F CONTROL operation.
HINT: The A/F CONTROL operation lowers the injection volume by 12.5 % or increases the injection volume by 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. Enter the following menus: 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:
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: The A/F sensor output has a few seconds of delay and the heated oxygen sensor output has about 20 seconds of delay at maximum.
The following A/F CONTROL procedure enables a technician to check the graph of the voltage outputs of both the A/F sensor and the heated oxygen sensor.
To display the graph, enter "ACTIVE TEST / A/F CONTROL / USER DATA", select "AFS B1S1 and O2S B1S2" by pressing "YES", and then "ENTER". Then press "F4".
HINT: 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, freeze frame data can help determine if the vehicle was running 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:
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 the connector.