P0031 Oxygen (A/F) Sensor Heater Control Circuit Low (Bank 1 Sensor 1)

 

DTC    P0031    Oxygen (A/F) Sensor Heater Control Circuit Low (Bank 1 Sensor 1)

DTC    P0032    Oxygen (A/F) Sensor Heater Control Circuit High (Bank 1 Sensor 1)


 

DESCRIPTION

HINT:

  1. For more information on the A/F sensor and TOYOTA D-CAT*, refer to the following procedures.
  2. These DTCs are related to the A/F sensor, although the titles say oxygen sensor.
*: Diesel Clean Advanced Technology.

 

The characteristic of the A/F sensor is such that it provides an output voltage*1 that is proportional to the air-fuel ratio that it is measuring. The A/F sensor output voltage is used as feedback to allow the ECM to control the A/F mixture.
The A/F sensor is located after the Diesel Particulate-NOx Reduction (DPNR) catalytic converter. This sensor has been developed based on the structure and technology of the A/F sensor that is used for gasoline engine. The cover for the sensor electrode has been modified to suit its application in a diesel engine. This change allows the sensor to function effectively in this TOYOTA D-CAT type diesel engine, and it also avoids problems with sensor temperature and particulate matter (PM).
In order to reduce both PM and nitrogen oxides (NOx), the ECM adjusts the air-fuel ratio to a mixture that is slightly richer than that which would otherwise be used (note that this mixture is still leaner than the stoichiometric air fuel ratio). The ECM bases these adjustments on signals that it receives from the A/F sensor.
When the ECM performs DPNR catalyst regeneration (cleaning) by adding fuel using the exhaust fuel addition injector, the A/F sensor feedback is used to ensure that an appropriate air fuel ratio is maintained.
*1: This voltage change occurs only inside the computer. It is not possible to measure this voltage at the sensor. The intelligent tester can be used to monitor this voltage.


ECD SYSTEM  2AD-FHV P0031    Oxygen A/F Sensor Heater Control Circuit Low Bank 1 Sensor 1  TOYOTA RAV4 / ACA30, 33, 38 ALA30

 

 

HINT:
 
The ECM provides a pulse width modulated control circuit to adjust current through the heater. The A/F sensor heater circuit uses a relay on the B+ side of the circuit.

 


ECD SYSTEM  2AD-FHV P0031    Oxygen A/F Sensor Heater Control Circuit Low Bank 1 Sensor 1  TOYOTA RAV4 / ACA30, 33, 38 ALA30


 

DTC No. DTC Detection Condition Trouble Area
P0031 A/F sensor heater current is 0.8 A or less when the heater operates
(1 trip detection logic)
  1. Open in A/F sensor heater circuit
  2. A/F sensor heater
  3. A/F sensor heater relay
  4. ECM
P0032 When either condition below is met:
  1. A/F sensor heater current is 10.4 A or more when the heater operates
    (1 trip detection logic)
  2. A/F sensor heater current is 0.8 A or more when the heater is not operating
    (1 trip detection logic)
  1. Short in A/F sensor heater circuit
  2. A/F sensor heater
  3. A/F

 

MONITOR DESCRIPTION

The inner surface of the A/F sensor element is exposed to outside air. The outer surface of the sensor element is exposed to exhaust gases. The sensor element is made of platinum coated zirconia and includes an integrated heating element. The zirconia element generates a small voltage when there is a large difference in the oxygen concentrations of the exhaust and the outside air. The platinum coating amplifies the voltage generation. When heated, the sensor becomes very efficient. If the temperature of the exhaust is low, the sensor will not generate useful voltage signals without supplemental heating. The ECM regulates the supplemental heating by using a duty-cycle approach to regulate the average current in the heater element. If the heater current is out of the normal range, the sensor's output signals will be inaccurate and the ECM cannot regulate the air-fuel ratio properly. When the heater current is out of the normal operating range, the ECM interprets this as a malfunction and sets a DTC.

 

WIRING DIAGRAM


ECD SYSTEM  2AD-FHV P0031    Oxygen A/F Sensor Heater Control Circuit Low Bank 1 Sensor 1  TOYOTA RAV4 / ACA30, 33, 38 ALA30



 

INSPECTION PROCEDURE

 

1.INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)


 

ECD SYSTEM  2AD-FHV P0031    Oxygen A/F Sensor Heater Control Circuit Low Bank 1 Sensor 1  TOYOTA RAV4 / ACA30, 33, 38 ALA30
  1. Disconnect the B62 A/F sensor connector.

  1. Measure the resistance of the terminals of the A/F sensor.

     

    Standard resistance:
    Tester Connection Connection Specified Condition
    B62-1 (HAF2) - B62-2 (+B) 20°C (68°F) 1.8 to 3.4 Ω

     

     

  1. Reconnect the A/F sensor connector.

 

  NG
REPLACE AIR FUEL RATIO SENSOR
 
OK  
 


 

2.CHECK AIR FUEL RATIO SENSOR (+B VOLTAGE)


 

ECD SYSTEM  2AD-FHV P0031    Oxygen A/F Sensor Heater Control Circuit Low Bank 1 Sensor 1  TOYOTA RAV4 / ACA30, 33, 38 ALA30
  1. Disconnect the B62 A/F sensor connector.

  1. Turn the ignition switch on (IG).

  1. Measure the voltage of the A/F sensor connector.

     

    Standard voltage:
    Tester Connection Specified Condition
    B62-2 (+B) - Body ground 9 to 14 V

     

     

  1. Reconnect the A/F sensor connector.

 

  NG
GO TO STEP 4
 
OK  
 

 

3.CHECK WIRE HARNESS (A/F SENSOR - ECM)
ECD SYSTEM  2AD-FHV P0031    Oxygen A/F Sensor Heater Control Circuit Low Bank 1 Sensor 1  TOYOTA RAV4 / ACA30, 33, 38 ALA30
  1. Disconnect the B62 A/F sensor connector.

  1. Disconnect the B32 ECM connector.

  1. Measure the resistance of the wire harness side connectors.

     

    Standard resistance:
    Tester Connection Specified Condition
    B62-1 (HAF2) - B32-104 (HAF2) Below 1 Ω
    B62-1 (HAF2) or B32-104 (HAF2) - Body ground 10 kΩ or higher

     

     

  1. Reconnect the A/F sensor connector.

  1. Reconnect the ECM connector.

 

  NG
REPAIR OR REPLACE HARNESS AND CONNECTOR
 
OK  
 
REPLACE ECM 

 

4.INSPECT INTEGRATION RELAY (A/F RELAY)
ECD SYSTEM  2AD-FHV P0031    Oxygen A/F Sensor Heater Control Circuit Low Bank 1 Sensor 1  TOYOTA RAV4 / ACA30, 33, 38 ALA30
  1. Remove the integration relay from the engine room No. 1 relay block.

  1. Inspect the A/F fuse.

    1. Remove the A/F fuse from the integration relay.

    2. Measure the resistance of the fuse.

       

      Standard resistance:
      Below 1 Ω

       

       

    3. Reinstall the A/F fuse.

     

  1. Inspect the A/F relay.

    1. Measure the A/F relay resistance.

       

      Standard resistance:
      Tester Connection Specified Condition
      1B-8 - 1C-1 10 kΩ or higher
      1B-8 - 1C-1 Below 1 Ω (Apply battery voltage to terminals 1B-6 and 1B-7)

       

       

    2. Reinstall the integration relay.

     

 

  NG
REPLACE INTEGRATION RELAY
 
OK  
 

 

5.CHECK WIRE HARNESS (A/F SENSOR - INTEGRATION RELAY - BODY GROUND)
ECD SYSTEM  2AD-FHV P0031    Oxygen A/F Sensor Heater Control Circuit Low Bank 1 Sensor 1  TOYOTA RAV4 / ACA30, 33, 38 ALA30
  1. Check the wire harness between the A/F sensor and integration relay.

    1. Disconnect the B62 A/F sensor connector.

    2. Remove the integration relay from the engine room No. 1 relay block.

    3. Measure the resistance of the wire harness side connector.

       

      Standard resistance:
      Tester Connection Specified Condition
      B62-2 (+B) - 1B-8 Below 1 Ω
      B62-2 (+B) or 1B-8 - Body ground 10 kΩ or higher

       

       

    4. Reconnect the A/F sensor connector.

     

  1. Check the wire harness between the integration relay and body ground.

    1. Measure the resistance of the wire harness side connector.

       

      Standard resistance:
      Tester Connection Specified Condition
      1B-7 - Body ground Below 1 Ω

       

       

    2. Reinstall the integration relay.

     

 

  MG
REPAIR OR REPLACE HARNESS AND CONNECTOR
 
OK  
 
REPLACE ECM