P0138
2AZ-FXE ENGINE CONTROL SYSTEM: SFI SYSTEM: P0136-P0139: Oxygen Sensor Circuit Malfunction (Bank 1 Sensor 2)
DTC P0136 - Oxygen Sensor Circuit Malfunction (Bank 1 Sensor 2)
DTC P0137 - Oxygen Sensor Circuit Low Voltage (Bank 1 Sensor 2)
DTC P0138 - Oxygen Sensor Circuit High Voltage (Bank 1 Sensor 2)
DTC P0139 - Oxygen Sensor Circuit Slow Response (Bank 1 Sensor 2)
DESCRIPTION
A three-way catalytic converter (TWC) is used in order to convert carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx) into less harmful substances. To allow the TWC to function effectively, it is necessary to keep the air-fuel ratio of the engine near the stoichiometric air-fuel ratio. To monitor the TWC, a Heated Oxygen (HO2) sensor is used.
The HO2 sensor is located behind the TWC, to detect the oxygen concentration in the exhaust gas. Since the sensor has an integrated heater for its sensing portion, it is possible to detect the oxygen concentration even when the intake air volume is low (the exhaust gas temperature is low).
When the air-fuel ratio becomes lean, the oxygen concentration in the exhaust gas is great. The HO2 sensor informs the ECM that the post-TWC oxygen concentration is great (low voltage, i.e. less than 0.45 V).
Conversely, when the air-fuel ratio is richer than the stoichiometric air-fuel level, the oxygen concentration in the exhaust gas becomes small. The HO2 sensor informs the ECM that the post-TWC oxygen concentration is small (high voltage, i.e. more than 0.45 V). The HO2 sensor output voltage changes drastically when the air-fuel ratio is close to the stoichiometric level.
The ECM uses the supplementary information from the HO2 sensor to determine the oxygen concentration after the TWC, and adjusts the fuel injection time accordingly. Thus, if the HO2 sensor is working improperly due to internal malfunctions, the ECM will be unable to monitor TWC operation.
MONITOR DESCRIPTION
Active Air-Fuel Ratio Control
The ECM (included in the hybrid vehicle control ECU) usually performs air-fuel ratio feedback control so that the Air-Fuel Ratio (A/F) sensor output indicates a near stoichiometric air-fuel level. This vehicle includes active air-fuel ratio control in addition to regular air-fuel ratio control. The ECM performs active air-fuel ratio control to detect any deterioration in the Three-Way Catalytic Converter (TWC) and Heated Oxygen (HO2) sensor malfunctions (refer to the diagram below).
Active air-fuel ratio control is performed for approximately 15 to 20 seconds while driving with a warm engine. During active air-fuel ratio control, the air-fuel ratio is forcibly regulated to become lean or rich by the ECM. If the ECM detects a malfunction, one of the following DTCs is set: DTC P0136 (abnormal voltage output), P0137 (open circuit) or P0138 (short circuit).
Abnormal Voltage Output of HO2 Sensor (DTC P0136)
While the ECM is performing active air-fuel ratio control, the air-fuel ratio is forcibly regulated to become rich or lean. If the sensor is not functioning properly, the voltage output variation is small. For example, when the HO2 sensor voltage does not decrease to less than 0.21 V and does not increase to more than 0.59 V during active air-fuel ratio control, the ECM determines that the sensor voltage output is abnormal and sets DTC P0136.
Open or Short in Heated Oxygen (HO2) Sensor Circuit (DTC P0137 or P0138)
During active air-fuel ratio control, the ECM calculates the Oxygen Storage Capacity (OSC)* of the Three-Way Catalytic Converter (TWC) by forcibly regulating the air-fuel ratio to become rich or lean. If the HO2 sensor has an open or short, or the voltage output of the sensor decreases significantly, the OSC indicates an extraordinarily high value. Even if the ECM attempts to continue regulating the air-fuel ratio to become rich or lean, the HO2 sensor output does not change.
While performing active air-fuel ratio control, when the target air-fuel ratio is rich and the HO2 sensor voltage output is 0.21 V or less (lean), the ECM interprets this as an abnormally low sensor output voltage and sets DTC P0137. When the target air-fuel ratio is lean and the voltage output is 0.59 V or more (rich) during active air-fuel ratio control, the ECM determines that the sensor voltage output is abnormally high, and sets DTC P0138.
HINT: DTC P0138 is also set if the HO2 sensor voltage output is more than 1.2 V for 10 seconds or more.
*: The TWC has the capability to store oxygen. The OSC and the emission purification capacity of the TWC are mutually related. The ECM determines whether the catalyst has deteriorated based on the calculated OSC value P0420.
High or Low Impedance of Heated Oxygen (HO2) Sensor (DTC P0136 or P0137)
During normal air-fuel ratio feedback control, there are small variations in the exhaust gas oxygen concentration. In order to continuously monitor the slight variations in the HO2 sensor signal while the engine is running, the impedance* of the sensor is measured by the ECM. The ECM determines that there is a malfunction in the sensor when the measured impedance deviates from the standard range.
*: The effective resistance in an alternating current electrical circuit.
HINT:
- The impedance cannot be measured using an ohmmeter.
- DTC P0136 indicates deterioration of the HO2 sensor. The ECM sets this DTC by calculating the impedance of the sensor when the typical enabling conditions are satisfied (2 driving cycles).
- DTC P0137 indicates an open or short circuit in the HO2 sensor (2 driving cycles). The ECM sets this DTC when the impedance of the sensor exceeds the threshold 15 kOhms.
Abnormal Voltage Output of Heated Oxygen (HO2) Sensor During Fuel-cut (DTC P0139)
The sensor output voltage drops to below 0.2 V (extremely Lean status) immediately when the vehicle decelerates and fuel cut is operating. If the voltage does not drop to below 0.2 V, the ECM determines that the sensor's response feature has deteriorated, illuminates the MIL and sets a DTC.
MONITOR STRATEGY
TYPICAL ENABLING CONDITIONS
All:
Heated Oxygen Sensor Output Voltage (Abnormal Voltage Output, High Voltage and Low Voltage):
Heated Oxygen Sensor Impedance (Low):
Heated Oxygen Sensor Impedance (High):
Heated Oxygen Sensor Output Voltage (Extremely High):
Heated Oxygen Sensor Voltage During Fuel Cut:
TYPICAL MALFUNCTION THRESHOLDS
Heated Oxygen Sensor Output Voltage (Abnormal Voltage Output):
Heated Oxygen Sensor Output Voltage (Low):
Heated Oxygen Sensor Output Voltage (High):
Heated Oxygen Sensor Impedance (Low):
Heated Oxygen Sensor Impedance (High):
Heated Oxygen Sensor Output Voltage (Extremely High):
Heated Oxygen Sensor Voltage During Fuel Cut:
COMPONENT OPERATING RANGE
MONITOR RESULT
Refer to CHECKING MONITOR STATUS Mode 6 Data.
WIRING DIAGRAM
CONFIRMATION DRIVING PATTERN
HINT:
- This confirmation driving pattern is used in the "PERFORM CONFIRMATION DRIVING PATTERN" procedure of the following diagnostic troubleshooting procedure.
- Performing this confirmation pattern will activate the Heated Oxygen (HO2) sensor monitor. (The catalyst monitor is performed simultaneously.) This is very useful for verifying the completion of a repair.
1. Connect the Techstream to the DLC3.
2. Turn the power switch on (IG).
3. Warm-up the engine until the engine coolant temperature reaches 75°C (167°F) or more [A].
4. Drive the vehicle at between 45 mph and 75 mph (70 km/h and 120 km/h) for at least 10 minutes [B].
5. Drive the vehicle at 60 mph (95 km/h) or more and decelerate the vehicle for 8 seconds or more. Perform this 3 times [C].
6. Turn the tester on.
7. Select the following menu items: Powertrain / Engine / Utility / All Readiness.
8. Input DTCs: P0136, P0137, P0138 and P0139.
- Check the DTC MONITOR is "NORMAL." If DTC MONITOR is "INCOMPLETE," perform the drive pattern increasing the vehicle speed and using the B position to decelerate the vehicle.
INSPECTION PROCEDURE
HINT: Malfunctioning areas can be identified by performing the Powertrain / Engine / Utility / All Readiness function provided in the Active Test. The Powertrain / Engine / Utility / All Readiness function can help to determine whether the Air Fuel Ratio (A/F) sensor, Heated Oxygen (HO2) sensor and other potential trouble areas are malfunctioning.
The following instructions describe how to conduct the Powertrain / Engine / Utility / All Readiness operation using the Techstream.
1. Connect the Techstream to the DLC3.
2. Put the engine in inspection mode Check Mode Procedure.
3. Turn the tester on.
4. Warm up the engine at an engine speed of 2500 rpm for approximately 90 seconds.
5. Select the following menu items: Powertrain / Engine / Active Test / Control the Injection Volume for A/F sensor.
6. Perform the Active Test operation with the engine idling (press the RIGHT or LEFT button to change the fuel injection volume).
7. Monitor the output voltages of the A/F and HO2 sensors (AFS B1 S1 and O2S B1 S2) displayed on the tester.
HINT:
- The Control the Injection Volume for A/F sensor operation lowers the fuel injection volume by 12.5% or increases the injection volume by 25%.
- Each sensor reacts in accordance with increases and decreases in the fuel injection volume.
NOTICE: The Air Fuel Ratio (A/F) sensor has an output delay of a few seconds and the Heated Oxygen (HO2) sensor has a maximum output delay of approximately 20 seconds.
- Following the Control the Injection Volume for A/F sensor or Control the Injection Volume for A/F sensor procedure enables technicians to check and graph the voltage outputs of both the A/F and HO2 sensors.
- To display the graph, select the following menu items: Powertrain / Engine / Active Test / Control the Injection Volume for A/F Sensor / A/F Control System / AFS B1 S1 or AFS B2 S1 and O2S B1 S2 or O2S B2 S2 then press the graph button on the Data List view.
HINT: Read freeze frame data using the Techstream. The ECM (included in the hybrid vehicle control ECU) records vehicle and driving condition as freeze frame data the moment a DTC is stored. 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.
PROCEDURE
1. READ DTC OUTPUT (DTC P0136, P0137 OR P0138)
(a) Connect the Techstream to the DLC3.
(b) Turn the power switch on (IG).
(c) Turn the tester on.
(d) Select the following menu items: Powertrain / Engine / Trouble Code.
(e) Read DTCs.
Result:
C -- READ VALUE USING TECHSTREAM (OUTPUT VOLTAGE OF HEATED OXYGEN SENSOR)
B -- CHECK FOR EXHAUST GAS LEAK
A -- Continue to next step.
2. READ VALUE USING TECHSTREAM (OUTPUT VOLTAGE OF HEATED OXYGEN SENSOR)
(a) Connect the Techstream to the DLC3.
(b) Turn the power switch on (IG).
(c) Turn the tester on.
(d) Select the following menu items: Powertrain / Engine / Data List / A/F Control System / O2S B1 S2.
(e) Allow the engine to idle.
(f) Read the Heated Oxygen (HO2) sensor output voltage while idling.
Result:
B -- INSPECT AIR FUEL RATIO SENSOR
A -- Continue to next step.
3. INSPECT HEATED OXYGEN SENSOR (CHECK FOR SHORT)
(a) Disconnect the heated oxygen sensor connector.
(b) Measure the resistance according to the value(s) in the table below.
Standard resistance:
(c) Reconnect the heated oxygen sensor connector.
NG -- REPLACE HEATED OXYGEN SENSOR
OK -- Continue to next step.
4. CHECK HARNESS AND CONNECTOR (CHECK FOR SHORT)
(a) Turn the power switch off and wait for 5 minutes or more.
(b) Disconnect the hybrid vehicle control ECU connector.
(c) Measure the resistance according to the value(s) in the table below.
Standard resistance:
(d) Reconnect the hybrid vehicle control ECU connector.
NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR
OK -- REPLACE HYBRID VEHICLE CONTROL ECU
5. INSPECT AIR FUEL RATIO SENSOR
HINT: This A/F sensor test is to check the A/F sensor current during fuel-cut. When the sensor is normal, the sensor current will indicate below 3.0 mA in this test.
(a) Connect the Techstream to the DLC3.
(b) Turn the power switch on (IG).
(c) Turn the tester on.
(d) Drive the vehicle according to the drive pattern listed below:
(1) Warm up the engine until the engine coolant temperature reaches 75°C (167°F) or more.
(2) Drive the vehicle at 40 mph (60 km/h) or more and decelerate the vehicle for 5 seconds or more.
(3) Repeat the deceleration above at least 3 times.
(e) Select the following menu items: Powertrain / Engine / Monitor / O2 Sensor / Details.
(f) Confirm that RANGE B1S1 is either PASS or FAIL. If the tester shows Incomplete, re-check RANGE B1S1 after performing the drive pattern.
(g) Select the RANGE B1S1.
(h) Read the Test Value.
Standard current:
Less than 3.0 mA
HINT: If the tester shows Incomplete again, increase vehicle speed and use the B position to decelerate the vehicle. Refer to the CONFIRMATION DRIVING PATTERN.
NG -- REPLACE AIR FUEL RATIO SENSOR
OK -- REPLACE HEATED OXYGEN SENSOR
6. READ VALUE USING TECHSTREAM (OUTPUT VOLTAGE OF HEATED OXYGEN SENSOR)
(a) Connect the Techstream to the DLC3.
(b) Turn the power switch on (IG).
(c) Turn the tester on.
(d) Start the engine.
(e) Select the following menu items: Powertrain / Engine / Data List / A/F Control System / O2S B1 S2.
(f) After warming up the engine, run the engine at an engine speed of 2500 rpm for 3 minutes.
(g) Read the output voltage of the heated oxygen sensor when the engine rpm is suddenly increased.
HINT: Quickly accelerate the engine to 4000 rpm 3 times using the accelerator pedal.
Standard:
Fluctuates between 0.4 V or less and 0.5 V or more.
NG -- CHECK FOR EXHAUST GAS LEAK
OK -- Continue to next step.
7. PERFORM ACTIVE TEST USING TECHSTREAM (INJECTION VOLUME)
(a) Connect the Techstream to the DLC3.
(b) Turn the power switch on (IG).
(c) Turn the tester on.
(d) Start the engine and warm it up.
(e) Select the following menu items: Powertrain / Engine / Active Test / Control the Injection Volume.
(f) Change the fuel injection volume using the tester, and monitor the voltage output of Air Fuel Ratio (A/F) and Heated Oxygen (HO2) sensors displayed on the tester.
HINT:
- Change the fuel injection volume within the range of -12% and +12%. The injection volume can be changed in 1% graduations within the range.
- The A/F sensor is displayed as AFS B1 S1 and the HO2 sensor is displayed as O2S B1 S2 on the Techstream.
Result:
HINT: A normal HO2 sensor voltage (O2S B1 S2) reacts in accordance with increases and decreases in fuel injection volumes. When the A/F sensor voltage remains at either less or more than 3.3 V despite the HO2 sensor indicating a normal reaction, the A/F sensor is malfunctioning.
NG -- REPLACE AIR FUEL RATIO SENSOR
OK -- CHECK ENGINE TO DETERMINE CAUSE OF EXTREMELY RICH OR LEAN ACTUAL AIR FUEL RATIO
8. CHECK FOR EXHAUST GAS LEAK
OK:
No gas leak.
NG -- REPAIR OR REPLACE EXHAUST GAS LEAK POINT
OK -- Continue to next step.
9. INSPECT HEATED OXYGEN SENSOR (HEATER RESISTANCE)
NG -- REPLACE HEATED OXYGEN SENSOR
OK -- Continue to next step.
10. CHECK HARNESS AND CONNECTOR (HEATED OXYGEN SENSOR - HYBRID VEHICLE CONTROL ECU)
(a) Disconnect the heated oxygen sensor connector.
(b) Turn the power switch on (IG).
(c) Measure the voltage between the +B terminal of HO2 sensor connector and body ground.
Standard voltage:
(d) Turn the power switch off.
(e) Disconnect the hybrid vehicle control ECU connector.
(f) Measure the resistance according to the value(s) in the table below.
Standard resistance (Check for open):
Standard resistance (Check for short):
(g) Reconnect the heated oxygen sensor connector.
(h) Reconnect the hybrid vehicle control ECU connector.
NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR
OK -- Continue to next step.
11. REPLACE HEATED OXYGEN SENSOR
(a) Replace the heated oxygen sensor Removal.
NEXT -- Continue to next step.
12. PERFORM CONFIRMATION DRIVING PATTERN
HINT: Refer to the CONFIRMATION DRIVING PATTERN.
NEXT -- Continue to next step.
13. CHECK WHETHER DTC OUTPUT RECURS (DTC P0136, P0137, P0138 OR P0139)
(a) Connect the Techstream to the DLC3.
(b) Turn the power switch on (IG).
(c) Turn the tester on.
(d) Select the following menu items: Powertrain / Engine / Utility / All Readiness.
(e) Input DTCs: P0136, P0137, P0138 and P0139.
(1) Check the DTC MONITOR is NORMAL. If DTC MONITOR is INCOMPLETE, perform the drive pattern increasing the vehicle speed and using the B position to decelerate the vehicle.
Result:
B -- REPLACE AIR FUEL RATIO SENSOR
A -- END
14. REPLACE AIR FUEL RATIO SENSOR
(a) Replace the air fuel ratio sensor Removal.
NEXT -- Continue to next step.
15. PERFORM CONFIRMATION DRIVING PATTERN
HINT: Refer to the CONFIRMATION DRIVING PATTERN.
NEXT -- Continue to next step.
16. CHECK WHETHER DTC OUTPUT RECURS (DTC P0136, P0137, P0138 OR P0139)
(a) Connect the Techstream to the DLC3.
(b) Turn the power switch on (IG).
(c) Turn the tester on.
(d) Select the following menu items: Powertrain / Engine / Utility / All Readiness.
(e) Input DTCs: P0136, P0137, P0138 and P0139.
(1) Check the DTC MONITOR is NORMAL. If DTC MONITOR is INCOMPLETE, perform the drive pattern increasing the vehicle speed and using the B position to decelerate the vehicle.
Result:
B -- REPLACE HEATED OXYGEN SENSOR
A -- END