Lexus IS250 · Service Manual ENGINE

P0031

Diagnostic trouble codes

DESCRIPTION

HINT:
  1. Although the DTC titles say oxygen sensor, these DTCs relate to the Air-Fuel Ratio (A/F) sensor.
  2. Sensor 1 refers to the sensor mounted in front of the Three-Way Catalytic Converter (TWC) and located near the engine assembly.

The A/F sensor generates voltage* that corresponds to the actual air-fuel ratio. This sensor voltage is used to provide the ECM with feedback so that it can control the air-fuel ratio. The ECM determines the deviation from the stoichiometric air-fuel ratio level, and regulates the fuel injection time. If the A/F sensor malfunctions, the ECM is unable to control the air-fuel ratio accurately.
The A/F sensor is the planar type and is integrated with the heater, which heats the solid electrolyte (zirconia element). This heater is controlled by the ECM. When the intake air volume is low (the exhaust gas temperature is low), a current flows into the heater to heat the sensor, in order to facilitate accurate oxygen concentration detection. In addition, the sensor and heater portions are narrower than the conventional type. The heat generated by the heater is conducted to the solid electrolyte though the alumina, therefore the sensor activation is accelerated.
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 level.
*: Value changes inside the ECM. Since the A/F sensor is the current output element, a current is converted to a voltage inside the ECM. Any measurements taken at the A/F sensor or ECM connectors will show a constant voltage.
A107164E10

HINT:
  1. When any of these DTCs are set, the ECM enters fail-safe mode. The ECM turns off the A/F sensor heater in fail-safe mode. Fail-safe mode continues until the engine switch is turned off.

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

    A103833E20

DTC No.
 DTC Detection Condition
 Trouble Area
P0031
P0051
 Air-Fuel Ratio (A/F) sensor heater (bank 1 sensor 1) current less than 0.8 A (1 trip detection logic)
  1. Open in A/F sensor heater (bank 1 sensor 1) circuit
  2. A/F sensor heater (bank 1 sensor 1)
  3. A/F HTR relay
  4. ECM
P0032
P0052
 Air-Fuel Ratio (A/F) sensor heater (bank 2 sensor 1) current more than 10 A (1 trip detection logic)
  1. Short in A/F sensor heater (bank 2 sensor 1) circuit
  2. A/F sensor heater (bank 2 sensor 1)
  3. A/F HTR relay
  4. ECM

HINT:
  1. Bank 1 refers to the bank that includes cylinder No. 1.
  2. Bank 2 refers to the bank that does not include cylinder No. 1.
  3. Sensor 1 refers to the sensor closest to the engine assembly.
  4. Sensor 2 refers to the sensor farthest away from the engine assembly.


WIRING DIAGRAM

A117875E01

INSPECTION PROCEDURE

HINT:
Read freeze frame data using the intelligent tester. Freeze frame data records the engine conditions when malfunctions are detected. When troubleshooting, freeze frame data can help determine if the vehicle was running or stopped, 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 (Click here).


1. INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)

  1. A085152E39
    Disconnect the E42 or E38 A/F sensor connector.

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

    Standard resistance (Bank 1 sensor 1):
    Tester Connection
    		 Condition
    		 Specified Condition
    HA1A (1) - +B (2)
    		 20°C (68°F)
    		 1.8 to 3.4 Ω
    HA1A (1) - A1A- (4)
    		 -
    		 10 kΩ or higher

    Standard resistance (Bank 2 sensor 1):
    Tester Connection
    		 Condition
    		 Specified Condition
    HA2A (1) - +B (2)
    		 20°C (68°F)
    		 1.8 to 3.4 Ω
    HA2A (1) - A2A- (4)
    		 -
    		 10 kΩ or higher

  1. Reconnect the A/F sensor connector.



 NG
REPLACE AIR FUEL RATIO SENSOR
OK


2. INSPECT A/F HTR RELAY

  1. B016200E03
    Remove the A/F HTR relay from the engine room J/B and R/B No. 2.

  1. Measure the resistance of the A/F HTR relay.

    Standard resistance:
    Tester Connection
    		 Specified Condition
    3 - 5
    		 10 kΩ or higher
    3 - 5
    		 Below 1 Ω
    (when battery voltage applied to terminals 1 and 2)

  1. Reinstall the A/F HTR relay.



 NG
REPLACE A/F HTR RELAY
OK


3. INSPECT ECM

  1. A126135E01
    Turn the engine switch on (IG).

  1. Measure the voltage of the E6 ECM connector.

    Standard voltage:
    Tester Connection
    		 Specified Condition
    HA1A (E6-6) - E04 (E6-5)
    		 9 to 14 V
    HA2A (E6-4) - E05 (E6-3)
    		 9 to 14 V

    HINT:
    1. The HA1A means the A/F sensor bank 1 sensor 1.
    2. The HA2A means the A/F sensor bank 2 sensor 1.



 OK
REPLACE ECM
NG


4. CHECK HARNESS AND CONNECTOR (A/F SENSOR - ECM, A/F SENSOR - A/F HTR RELAY)

  1. A107393E10
    Check the wire harness and the connector between the ECM and the A/F sensor ECM and body ground.

    1. Disconnect the E42 or E38 A/F sensor connector.

    2. Disconnect the E6 ECM connector.

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

      Standard resistance (Check for open):
      Tester Connection
      		 Specified Condition
      HA1A (E42-1) - HA1A (E6-6)
      		 Below 1 Ω
      HA2A (E38-1) - HA2A (E6-4)
      		 Below 1 Ω
      E04 (E6-5) - Body ground
      		 Below 1 Ω
      E05 (E6-3) - Body ground
      		 Below 1 Ω

      Standard resistance (Check for short):
      Tester Connection
      		 Specified Condition
      HA1A (E42-1) or HA1A (E6-6) - Body ground
      		 10 kΩ or higher
      HA2A (E38-1) or HA2A (E6-4) - Body ground
      		 10 kΩ or higher

    4. Reconnect the A/F sensor connector.

    5. Reconnect the ECM connector.

  1. Check the wire harness and the connector between the A/F sensor and A/F HTR relay.

    1. Disconnect the E42 or E38 A/F sensor connector.

    2. Remove the A/F HTR relay from the engine room J/B and R/B No. 2.

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

      Standard resistance (Check for open):
      Tester Connection
      		 Specified Condition
      +B (E42-2) - A/F HTR relay (3)
      		 Below 1 Ω
      +B (E38-2) - A/F HTR relay (3)
      		 Below 1 Ω

      Standard resistance (Check for short):
      Tester Connection
      		 Specified Condition
      +B (E42-2) or A/F HTR relay (3) - Body ground
      		 10 kΩ or higher
      +B (E38-2) or A/F HTR relay (3) - Body ground
      		 10 kΩ or higher

    4. Reconnect the A/F sensor connector.

    5. Reinstall the A/F HTR relay.



 NG
REPAIR OR REPLACE HARNESS OR CONNECTOR
OK

REPLACE ECM


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