Toyota Tundra Service Manual: Oxygen Sensor Circuit (Bank 1 Sensor 2) (P0136-P0139,P013A,P013C,P0156-P0159)

DESCRIPTION

In order to obtain a high purification rate of the carbon monoxide (CO), hydrocarbon (HC) and nitrogen oxide (NOx) components in the exhaust gas, a TWC is used. For the most efficient use of the TWC, the air-fuel ratio must be precisely controlled so that it is always close to the stoichiometric air-fuel ratio. For the purpose of helping the ECM to deliver accurate air-fuel ratio control, a Heated Oxygen (HO2) sensor is used.

The HO2 sensor is located behind the TWC, and detects the oxygen concentration in the exhaust gas. Since the sensor is integrated with the heater that heats the 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 rich. The HO2 sensor informs the ECM that the post-TWC air-fuel ratio is lean (low voltage, i.e. less than 0.45 V).

Conversely, when the air-fuel ratio is richer than the stoichiometric air-fuel ratio, the oxygen concentration in the exhaust gas becomes lean. The HO2 sensor informs the ECM that the post-TWC air-fuel ratio is rich (high voltage, i.e. more than 0.45 V). The HO2 sensor has the property of changing its output voltage drastically when the air-fuel ratio is close to the stoichiometric level.

The ECM uses the supplementary information from the HO2 sensor to determine whether the air-fuel ratio after the TWC is rich or lean, and adjusts the fuel injection time accordingly. Thus, if the HO2 sensor is working improperly due to internal malfunctions, the ECM is unable to compensate for deviations in the primary air-fuel ratio control.

MONITOR DESCRIPTION

1. Active Air-Fuel Ratio Control

The ECM 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, a DTC is stored.

2. Abnormal Voltage Output of Heated Oxygen (HO2) Sensor (DTC P0136 and P0156)

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 increase to more than 0.66 V during active air-fuel ratio control, the ECM determines that the sensor voltage output is abnormal and stores DTC P0136 or P0156.

3. Open in Heated Oxygen (HO2) Sensor Circuit (DTC P0137 and P0157)

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 the voltage output of the sensor noticeably decreases, 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 stores DTC P0137 or P0157.

HINT:

*: 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 (See page ).

4. High or Low Impedance of Heated Oxygen (HO2) Sensor (DTC P0136 and P0156 or P0137 and P0157)

During normal air-fuel ratio feedback control, there are small variations in the exhaust gas oxygen concentration. In order to continuously monitor the slight variation of 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.
• DTCs P0136 and P0156 indicate the deterioration of the HO2 sensor. The ECM stores the DTCs by calculating the impedance of the sensor when the typical enabling conditions are satisfied (2 driving cycles).
• DTCs P0137 and P0157 indicate an open or short circuit in the HO2 sensor (2 driving cycles). The ECM stores the DTCs when the impedance of the sensor exceeds the threshold 15 kΩ.

5. Extremely High Output Voltage of Heated Oxygen (HO2) Sensor (DTC P0138 or P0158)

The ECM continuously monitors the HO2 sensor output voltage while the engine is running.

DTC P0138 or P0158 is stored if the HO2 sensor voltage output is more than 1.2 V for 10 seconds or more.

6. Heated Oxygen Sensor Output Voltage During Fuel Cut (P0139 or P0159)

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 when accumulated intake air mass is more than 15.3 g, the system determines that the sensor response has deteriorated, illuminates the MIL and stores a DTC.

7. Abnormal Voltage Output of Heated Oxygen Sensor during Fuel Cut from Rich Condition (P013A and P013C)

If the sensor output voltage does not drop from 0.35 to 0.2 V immediately when the vehicle decelerates and fuel cut is operating, the ECM illuminates the MIL and stores a DTC.

MONITOR STRATEGY

TYPICAL ENABLING CONDITIONS

TYPICAL MALFUNCTION THRESHOLDS

COMPONENT OPERATING RANGE

MONITOR RESULT

Refer to Checking Monitor Status (See page ).

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 driving 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 ignition switch to ON and turn the Techstream on.
3. Clear the DTCs (even if no DTCs are stored, perform the clear DTC operation).
4. Turn the ignition switch off and wait for at least 30 seconds.
5. Turn the ignition switch to ON and turn the Techstream on [A].
6. Start the engine and warm it up until the ECT reaches 75°C (167°F) or higher [B].
7. With the transmission in 4th gear or higher, drive the vehicle at 60 to 120 km/h (37 to 75 mph) for 10 minutes or more [C].

   CAUTION:

   When performing the confirmation driving pattern, obey all speed limits and traffic laws.

8. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes [D].
9. Read the pending DTCs.

   HINT:

   • If a pending DTC is output, the system is malfunctioning.
   • If a pending DTC is not output, perform the following procedure.
10. Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.
11. Input the DTC: P0136, P0137, P0138, P0156, P0157 or P0158.
12. Check the DTC judgment result.

    Techstream Display	Description
    NORMAL	DTC judgment completed System normal
    ABNORMAL	DTC judgment completed System abnormal
    INCOMPLETE	DTC judgment not completed Perform driving pattern after confirming DTC enabling conditions
    N/A	Unable to perform DTC judgment Number of DTCs which do not fulfill DTC preconditions has reached ECU memory limit

    HINT:

    • If the judgment result shows NORMAL, the system is normal.
    • If the judgment result shows ABNORMAL, the system has a malfunction.
    • If the judgment result shows INCOMPLETE or N/A, perform steps [C] through [D].
13. If no pending DTC is output, perform a universal trip and check for permanent DTCs (See page ).

    HINT:

    • If a permanent DTC is output, the system is malfunctioning.
    • If no permanent DTC is output, the system is normal.

1. Connect the Techstream to the DLC3.
2. Turn the ignition switch to ON.
3. Turn the Techstream on.
4. Clear DTCs (even if no DTCs are stored, perform the clear DTC operation).
5. Turn the ignition switch off and wait for at least 30 seconds.
6. Turn the ignition switch to ON and turn the Techstream on.
7. Enter the following menus: Powertrain / Engine and ECT / Monitor / Current Monitor.
8. Check that Catalyst Efficiency / Current is Incomplete.
9. Start the engine and warm it up until the engine coolant temperature is 75°C (167°F) or higher [A].
10. Drive the vehicle at approximately 60 km/h (37 mph) for 10 minutes or more [B].

    CAUTION:

    When performing the confirmation driving pattern, obey all speed limits and traffic laws.

    HINT:

    Drive the vehicle while keeping the engine load as constant as possible.

11. Drive the vehicle at 60 km/h (37 mph), and then decelerate the vehicle by releasing the accelerator pedal for 5 seconds or more to perform the fuel-cut [C].

    CAUTION:

    When performing the confirmation driving pattern, obey all speed limits and traffic laws.

12. Enter the following menus: Powertrain / Engine and ECT / Monitor / Current Monitor / O2 Sensor / RL F/C B1S2, RL F/C B2S2 [D].
13. Check the Test Value for RL F/C B1S2, RL F/C B2S2.

    HINT:

    If Test Value displays 0, perform step [C] until it displays a value larger than 0, as the O2 sensor monitor is not finished.

14. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.
15. Read the pending DTC [D].

    HINT:

    • If a pending DTC is output, the system is malfunctioning.
    • If a pending DTC is not output, perform the following procedure.
16. Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.
17. Input the DTC: P0139, P013A, P013C or P0159.
18. Check the DTC judgment result.

    Techstream Display	Description
    NORMAL	DTC judgment completed System normal
    ABNORMAL	DTC judgment completed System abnormal
    INCOMPLETE	DTC judgment not completed Perform driving pattern after confirming DTC enabling conditions
    N/A	Unable to perform DTC judgment Number of DTCs which do not fulfill DTC preconditions has reached ECU memory limit

    HINT:

    • If the judgment result shows ABNORMAL, the system has a malfunction.
    • If the judgment result shows NORMAL, the system is normal.
    • If the judgment result shows INCOMPLETE or N/A, drive the vehicle with the shift lever in S, and then perform step [C] again.
19. If no pending DTC is output, perform a universal trip and check for permanent DTCs (See page ).

    HINT:

    • If a permanent DTC is output, the system is malfunctioning.
    • If no permanent DTC is output, the system is normal.

WIRING DIAGRAM

CAUTION / NOTICE / HINT

HINT:

Malfunctioning areas can be identified by performing the Control the Injection Volume for A/F Sensor function provided in the Active Test. The Control the Injection Volume for A/F Sensor 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 Control the Injection Volume for A/F Sensor operation using the Techstream.

1. Connect the Techstream to the DLC3.
2. Start the engine and turn the Techstream on.
3. Warm up the engine at an engine speed of 2500 rpm for approximately 90 seconds.
4. Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor.
5. Perform the Active Test operation with the engine in an idling condition (press the RIGHT or LEFT button to change the fuel injection volume).
6. Monitor the output voltages of the A/F and HO2 sensors (AFS Voltage B1S1 and O2S B1S2 or AFS Voltage B2S1 and O2S B2S2) displayed on the Techstream.

HINT:

• Change the fuel injection volume within the range of -12.5% to +12.5%.
• The air fuel ratio sensor has an output delay of a few seconds and the heated oxygen sensor has a maximum output delay of approximately 20 seconds.
• If the sensor output voltage does not change (almost no reaction) while performing the Active Test, the sensor may be malfunctioning.

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.

HINT:

• Following the 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, enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor / Data List / AFS Voltage B1S1 and O2S B1S2 or AFS Voltage B2S1 and O2S B2S2.
• Read freeze frame data using the Techstream. Freeze frame data records the engine condition 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 will be set.
• If the OX2B wire from the ECM connector is short-circuited to the +B wire, DTC P0156 will be set.
• Bank 1 refers to the bank that includes the No. 1 cylinder*.

  *: The No. 1 cylinder is the cylinder which is farthest from the transmission.

• Bank 2 refers to the bank that does not include the No. 1 cylinder.
• Sensor 1 refers to the sensor closest to the engine assembly.
• Sensor 2 refers to the sensor farthest away from the engine assembly.

PROCEDURE

(a) Connect the Techstream to the DLC3.

(b) Turn the ignition switch to ON.

(c) Turn the Techstream on.

(d) Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.

(e) Read DTCs.

B

GO TO STEP 8

C

GO TO STEP 4

D

GO TO STEP 21

E

GO TO DTC CHART

A

(a) Disconnect the HO2 sensor connector.

(b) Measure the resistance according to the value(s) in the table below.

Standard Resistance:

HINT:

Perform "Inspection After Repair" after replacing the heated oxygen sensor (See page ).

NG

REPLACE HEATED OXYGEN SENSOR

OK

(a) Turn the ignition switch off and wait for 5 minutes.

(b) Disconnect the ECM connector.

(c) Measure the resistance according to the value(s) in the table below.

Standard Resistance:

OK

REPLACE ECM

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

(a) Connect the Techstream to the DLC3.

(b) Start the engine.

(c) Turn the Techstream on.

(d) Warm up the engine.

(e) Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor / Data List / O2S B1S2 or O2S B2S2.

(f) Change the fuel injection volume using the Techstream, monitoring the voltage output of the HO2 sensors displayed on the Techstream.

HINT:

• Change the fuel injection volume within the range of -12.5% to +12.5%.
• The air fuel ratio sensor has an output delay of a few seconds and the heated oxygen sensor has a maximum output delay of approximately 20 seconds.

Standard voltage:

Fluctuates between 0.4 V or less and 0.55 V or more.

NG

GO TO STEP 8

OK

(a) Connect the Techstream to the DLC3.

(b) Turn the Techstream on.

(c) Start the engine.

(d) Warm up the engine.

(e) Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor.

(f) Change the fuel injection volume using the Techstream, and monitor the voltage output of the Air-Fuel Ratio (A/F) and HO2 sensors displayed on the Techstream.

HINT:

• Change the fuel injection volume within the range of -12.5% to +12.5%.
• The A/F sensor is displayed as AFS Voltage B1S1 or AFS Voltage B2S1, and the HO2 sensor is displayed as O2S B1S2 or O2S B2S2 on the Techstream.
• The air fuel ratio sensor has an output delay of a few seconds and the heated oxygen sensor has a maximum output delay of approximately 20 seconds.
• If the sensor output voltage does not change (almost no reaction) while performing the Active Test, the sensor may be malfunctioning. Result

  Techstream Display (Sensor)	Voltage Variation	Proceed to
  AFS Voltage B1S1 AFS Voltage B2S1	Alternates between more and less than 3.3 V	OK
  	Remains at more than 3.3 V	NG
  	Remains at less than 3.3 V	NG

  HINT:

  A normal HO2 sensor voltage (O2S B1S2 or O2S B2S2) 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

GO TO STEP 16

OK

(a) Connect the Techstream to the DLC3.

(b) Start the engine and warm it up until the engine coolant temperature reaches 75°C (167°F) or higher.

HINT:

• When performing the Active Test, make sure the shift lever is in P or N.
• The A/C switch and all accessory switches should be off.

(c) Turn the Techstream on.

(d) Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the EGR Step Position.

(e) Confirm the Throttle Idle Position is ON and check the engine idling condition and MAP values in the Data List while performing the Active Test.

HINT:

• Do not leave the EGR valve open for 10 seconds or more during the Active Test.
• Be sure to return the EGR valve to step 0 when the Active Test is completed.

OK:

MAP and idling condition change in response to EGR step position as follows.

Standard:

OK

CHECK EXTREMELY RICH OR LEAN ACTUAL AIR FUEL RATIO AND REPAIR CAUSE (FUEL INJECTOR ASSEMBLY, FUEL PRESSURE, GAS LEAK FROM SYSTEM)

NG

(a) Remove the EGR valve assembly (See page ).

(b) Check if the EGR valve is stuck open.

OK:

EGR valve is tightly closed.

HINT:

Perform "Inspection After Repairs" after replacing the EGR valve assembly (See page ).

OK

CHECK EXTREMELY RICH OR LEAN ACTUAL AIR FUEL RATIO AND REPAIR CAUSE (FUEL INJECTOR ASSEMBLY, FUEL PRESSURE, GAS LEAK FROM SYSTEM)

NG

REPLACE EGR VALVE ASSEMBLY

(a) Check for exhaust gas leak.

OK:

No gas leak.

HINT:

Perform "Inspection After Repair" after repairing or replacing the exhaust system (See page ).

NG

REPAIR OR REPLACE EXHAUST GAS LEAK POINT

OK

NG

REPLACE HEATED OXYGEN SENSOR

OK

(a) Disconnect the HO2 sensor connector.

(b) Disconnect the ECM connector.

(c) Measure the resistance according to the value(s) in the table below.

Standard Resistance:

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

(a) Replace the heated oxygen sensor (See page ).

HINT:

Perform "Inspection After Repair" after replacing the heated oxygen sensor (See page ).

NEXT

(a) Perform the Confirmation Driving Pattern (P0136, P0137, P0138, P0156, P0157 and P0158).

NEXT

(a) Connect the Techstream to the DLC3.

(b) Turn the Techstream on.

(c) Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.

(d) Input DTCs: P0136, P0137, P0138, P0156, P0157 and P0158.

(e) Check that the DTC monitor is NORMAL. If the DTC monitor is INCOMPLETE, perform the drive pattern increasing the vehicle speed.

B

END

A

(a) Connect the Techstream to the DLC3.

(b) Start the engine and warm it up until the engine coolant temperature reaches 75°C (167°F) or higher.

HINT:

• When performing the Active Test, make sure the shift lever is in P or N.
• The A/C switch and all accessory switches should be off.

(c) Turn the Techstream on.

(d) Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the EGR Step Position.

(e) Confirm the Throttle Idle Position is ON and check the engine idling condition and MAP values in the Data List while performing the Active Test.

HINT:

• Do not leave the EGR valve open for 10 seconds or more during the Active Test.
• Be sure to return the EGR valve to step 0 when the Active Test is completed.

OK:

MAP and idling condition change in response to EGR step position as follows.

Standard:

HINT:

Perform "Inspection After Repair" after replacing the air fuel ratio sensor (See page ).

OK

REPLACE AIR FUEL RATIO SENSOR

NG

(a) Remove the EGR valve assembly (See page ).

(b) Check if the EGR valve is stuck open.

OK:

EGR valve is tightly closed.

HINT:

Perform "Inspection After Repair" after replacing the EGR valve assembly or air fuel ratio sensor (See page ).

OK

REPLACE AIR FUEL RATIO SENSOR

NG

REPLACE EGR VALVE ASSEMBLY

(a) Replace the air fuel ratio sensor (See page ).

HINT:

Perform "Inspection After Repair" after replacing the air fuel ratio sensor (See page ).

NEXT

(a) Perform the Confirmation Driving Pattern (P0136, P0137, P0138, P0156, P0157 and P0158).

NEXT

(a) Connect the Techstream to the DLC3.

(b) Turn the Techstream on.

(c) Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.

(d) Input DTCs: P0136, P0137, P0138, P0156, P0157 and P0158.

(e) Check that the DTC monitor is NORMAL. If the DTC monitor is INCOMPLETE, perform the drive pattern increasing the vehicle speed.

B

END

A

(a) Connect the Techstream to the DLC3.

(b) Start the engine and warm it up until the engine coolant temperature reaches 75°C (167°F) or higher.

HINT:

• When performing the Active Test, make sure the shift lever is in P or N.
• The A/C switch and all accessory switches should be off.

(c) Turn the Techstream on.

(d) Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the EGR Step Position.

(e) Confirm the Throttle Idle Position is ON and check the engine idling condition and MAP values in the Data List while performing the Active Test.

HINT:

• Do not leave the EGR valve open for 10 seconds or more during the Active Test.
• Be sure to return the EGR valve to step 0 when the Active Test is completed.

OK:

MAP and idling condition change in response to EGR step position as follows.

Standard:

HINT:

Perform "Inspection After Repair" after replacing the heated oxygen sensor (See page ).

OK

REPLACE HEATED OXYGEN SENSOR

NG

(a) Remove the EGR valve assembly (See page ).

(b) Check if the EGR valve is stuck open.

OK:

EGR valve is tightly closed.

HINT:

Perform "Inspection After Repair" after replacing the EGR valve assembly or heated oxygen sensor (See page ).

OK

REPLACE HEATED OXYGEN SENSOR

NG

REPLACE EGR VALVE ASSEMBLY

(a) Check for exhaust gas leak.

OK:

No gas leak.

HINT:

Perform "Inspection After Repair" after repairing or replacing the exhaust system (See page ).

NG

REPAIR OR REPLACE EXHAUST GAS LEAK POINT

OK

(a) Turn the ignition switch off and wait for 5 minutes.

(b) Disconnect the ECM connector.

(c) Measure the resistance according to the value(s) in the table below.

Standard Resistance:

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

(a) Perform the Confirmation Driving Pattern (P0139, P013A, P013C and P0159).

NEXT

(a) Connect the Techstream to the DLC3.

(b) Turn the Techstream on.

(c) Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.

(d) Input DTCs: P0139, P013A, P013C or P0159.

(e) Check that the DTC monitor is NORMAL. If the DTC monitor is INCOMPLETE, perform the drive pattern increasing the vehicle speed.

B

CHECK FOR INTERMITTENT PROBLEMS

A

(a) Connect the Techstream to the DLC3.

(b) Start the engine and warm it up until the engine coolant temperature reaches 75°C (167°F) or higher.

HINT:

• When performing the Active Test, make sure the shift lever is in P or N.
• The A/C switch and all accessory switches should be off.

(c) Turn the Techstream on.

(d) Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the EGR Step Position.

(e) Confirm the Throttle Idle Position is ON and check the engine idling condition and MAP values in the Data List while performing the Active Test.

HINT:

• Do not leave the EGR valve open for 10 seconds or more during the Active Test.
• Be sure to return the EGR valve to step 0 when the Active Test is completed.

OK:

MAP and idling condition change in response to EGR step position as follows.

Standard:

HINT:

Perform "Inspection After Repair" after replacing the heated oxygen sensor (See page ).

OK

REPLACE HEATED OXYGEN SENSOR

NG

(a) Remove the EGR valve assembly (See page ).

(b) Check if the EGR valve is stuck open.

OK:

EGR valve is tightly closed.

HINT:

Perform "Inspection After Repair" after replacing the EGR valve assembly or heated oxygen sensor (See page ).

OK

REPLACE HEATED OXYGEN SENSOR

NG

REPLACE EGR VALVE ASSEMBLY