Conditioning For Sensor Testing

1. WAVEFORMS OF AIR-FUEL RATIO (A/F) AND HEATED OXYGEN (HO2) SENSORS 

   HINT:

   Perform the operation with the engine speeds and time durations described below prior to check the waveforms of the A/F and HO2 sensors. This is in order to activate the sensors sufficiently to obtain the appropriate inspection results.

   Fig 1: Waveforms Of Air-Fuel Ratio (A/F) And Heated Oxygen (HO2) Sensors

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
   1. Connect an intelligent tester or OBD II scan tool to the DLC3 (Procedure "A").
   2. Start the engine and warm it up with all the accessories switched OFF, until the engine coolant temperature stabilizes (Procedure "B").
   3. Run the engine at an engine speed of between 2,500 rpm and 3,000 rpm for at least 3 minutes (Procedure "C").
   4. While running the engine at 3,000 rpm for 2 seconds and 2,000 rpm for 2 seconds, check the waveforms of the A/F and HO2 sensors using the tester or scan tool (Procedure "D").

      HINT:

      • If either of the voltage outputs of the Air-Fuel Ratio (A/F) or Heated Oxygen (HO2) sensors does not fluctuate, or either of the sensors makes a noise, the sensor may be malfunctioning.
      • If the voltage outputs of both the sensors remain lean or rich, the air-fuel ratio may be extremely lean or rich. In such cases, perform the following A/F CONTROL using an intelligent tester.
      • If the Three-Way Catalytic Converter (TWC) has deteriorated, the HO2 sensor (located behind the TWC) voltage output fluctuates up and down frequently, even under normal driving conditions (active air-fuel ratio control is not performed).
        Fig 2: Voltage Output When Active Air Fuel Ratio Control Is Not Performed

        Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
2. A/F CONTROL 

   HINT:

   Intelligent tester only:

   Malfunctioning areas can be identified by performing the A/F CONTROL function provided in the ACTIVE TEST. The A/F CONTROL 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 A/F CONTROL operation using an intelligent tester.

   1. Connect an intelligent tester to the DLC3.
   2. Start the engine and turn the tester ON.
   3. Warm up the engine at an engine speed of 2,500 rpm for approximately 90 seconds.
   4. On the 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 in an idling condition (press the RIGHT or LEFT button to change the fuel injection volume).
   6. Monitor the voltage outputs of the A/F and HO2 sensors (AFS B1S1 and OS2 B1S2) displayed on the tester.

      HINT:

      • The A/F CONTROL 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.

Standard voltage 

Fig 3: A/F Sensor And HO2 Sensor Output Voltage Graph

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

HINT:

• Following the A/F CONTROL 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 on the tester: DIAGNOSIS / ENHANCED OBD II / ACTIVE TEST / A/F CONTROL / USER DATA / AFS B1S1 and O2S B1S2, and press the YES button and then the ENTER button followed by the F4 button.