Inspection Procedure

HINT:

Read freeze frame data using a intelligent tester. Freeze frame data record 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.

1. INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE) 
   1. Disconnect the A4 Air-Fuel Ratio (A/F) sensor connector.
   2. Measure the resistance between the terminals of the A/F sensor connector.

      Standard Resistance 

      RESISTANCE REFERENCE CHART
      
      

      Tester Connections	Specified Conditions
      HA1A (1) - +B (2)	1.8 Ω to 3.4 Ω at 20°C (680°F)
      HA1A (1) - A1A- (4)	10 kΩ or higher

   3. Reconnect the A/F sensor connector.
   Fig 1: Identifying A4 Air-Fuel Ratio (A/F) Sensor Connector Terminals
   Courtesy of TOYOTA MOTOR SALES, U.S.A., INC.

   NG: REPLACE AIR FUEL RATIO SENSOR 

   OK: Go to Next Step 

2. INSPECT AIR FUEL RATIO SENSOR HEATER RELAY (A/F HEATER RELAY) 
   1. Remove the A/F HEATER relay from the engine room R/B.
   2. Check the A/F HEATER relay resistance.

      Standard Resistance 

      RESISTANCE REFERENCE CHART
      
      

      Tester Connections	Specified Conditions
      3 - 5	10 kΩ or higher
      3 - 5	Below 1 Ω (when battery voltage applied to terminals 1 and 2)

   3. Reinstall the A/F HEATER relay.
   Fig 2: Checking Circuit Opening Relay Resistance
   Courtesy of TOYOTA MOTOR SALES, U.S.A., INC.

   NG: REPLACE AIR FUEL RATIO SENSOR HEATER RELAY 

   OK: Go to Next Step 

3. INSPECT ECM (HA1A VOLTAGE) 
   1. Turn the ignition switch to ON.
   2. Measure the voltage between the terminals of the E4 and E5 ECM connectors.

      Standard Voltage 

      VOLTAGE CHART
      
      

      Tester Connections	Specified Conditions
      HA1A (E4-1) - E04 (E5-7)	9 to 14 V

   Fig 3: Identifying Terminals Of E4 And E5 ECM Connectors

   Courtesy of TOYOTA MOTOR SALES, U.S.A., INC.

   OK : REPLACE ECM 

   NG: Go to Next Step 

4. CHECK HARNESS AND CONNECTOR (A/F SENSOR - ECM, A/F SENSOR - A/F HEATER RELAY) 
   1. Check the harness and connectors between the ECM and A/F sensor.
      1. Disconnect the A4 A/F sensor connector.
      2. Disconnect the E4 ECM connector.
      3. Check the resistance.

         Standard Resistance (Check for open) 

         RESISTANCE REFERENCE CHART
         
         

         Tester Connections	Specified Conditions
         HA1A (A4-1) - HA1A (E4-1)	Below 1 Ω

         Standard Resistance (Check for short) 

         RESISTANCE REFERENCE CHART
         
         

         Tester Connections	Specified Conditions
         HA1A (A4-1) or HA1A (E4-1) - Body ground	10 kΩ or higher

      4. Reconnect the A/F sensor connector.
      5. Reconnect the ECM connector.
   2. Check the harness and connector between the A/F sensor and A/F HEATER relay.
      1. Disconnect the A4 A/F sensor connector.
      2. Remove the A/F HEATER relay from the engine room R/B.
      3. Check the resistance.

         Standard Resistance (Check for open) 

         RESISTANCE REFERENCE CHART
         
         

         Tester Connections	Specified Conditions
         +B (A4-2) - A/F HEATER relay (3)	Below 1 Ω

         Standard Resistance (Check for short) 

         RESISTANCE REFERENCE CHART
         
         

         Tester Connections	Specified Conditions
         +B (A4-2) or A/F HEATER relay (3) - Body ground	10 kΩ or higher

      4. Reconnect the A/F sensor connector.
      5. Reinstall the A/F HEATER relay.
   Fig 4: Identifying A/F Sensor, ECM, A/F Sensor And A/F Heater Relay
   Courtesy of TOYOTA MOTOR SALES, U.S.A., INC.

   OK : REPLACE ECM 

   NG: REPAIR OR REPLACE HARNESS OR CONNECTOR