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.
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 Part 1:
Typical Malfunction Thresholds Part 2:
Component Operating Range:
The ECM monitors the rear heated oxygen sensor (HO2S) in the following 3 items:
1. The HO2S voltage changes between Rich (more than 0.45 V) and Lean (less than 0.45 V) while the vehicle is running (repeating acceleration and deceleration) for 8 minutes. If not, the ECM interprets this as a malfunction, illuminates the MIL, and then sets a DTC.
2. The HO2S voltage does not remain at less than 0.05 V for a long time while the vehicle is running (60% of the time in the 220 seconds monitor, the sensor output is less than 0.05 V). If it does, the ECM interprets this as a malfunction, illuminates the MIL, and then sets a DTC.
3. The sensor's voltage drops to below 0.2 V (extremely Lean status) immediately when the vehicle decelerates and the fuel cut is working for 6 seconds. If not, the ECM interprets this to mean the sensor's response feature has deteriorated, illuminates the MIL, and then sets a DTC.
O2S TEST RESULT (MODE 05)
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.