P0031

1UR-FSE ENGINE CONTROL SYSTEM: SFI SYSTEM: P0031, P0032, P0051, P0052: Oxygen (A/F) Sensor Heater Control Circuit Low (Bank 1 Sensor 1)
P0052 - Oxygen (A/F) Sensor Heater Control Circuit High (Bank 2 Sensor 1)

DESCRIPTION

HINT
- Although the DTC titles include oxygen sensor, these DTCs relate to the Air-Fuel Ratio (A/F) sensor.
- 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 through 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.





HINT
- 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.
- 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.










HINT
- Bank 1 refers to the bank that includes No. 1 cylinder.
- Bank 2 refers to the bank that does not include 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.

MONITOR DESCRIPTION

1. The ECM uses information from the Air-Fuel Ratio (A/F) sensor to regulate the air-fuel ratio and keep it close to the stoichiometric level. This maximizes the ability of the Three-Way Catalytic Converter (TWC) to purify the exhaust gases.

2. The A/F sensor detects oxygen levels in the exhaust gas and transmits the information to the ECM. The inner surface of the sensor element is exposed to the outside air. The outer surface of the sensor element is exposed to the exhaust gas. The sensor element is made of platinum coated zirconia and includes an integrated heating element.

3. The zirconia element generates a small voltage when there is a large difference in the oxygen concentrations between the exhaust gas and outside air. The platinum coating amplifies this voltage generation.

4. The A/F sensor is more efficient when heated. When the exhaust gas temperature is low, the sensor cannot generate useful voltage signals without supplementary heating. The ECM regulates the supplementary heating using a duty-cycle approach to adjust the average current in the sensor heater element. If the heater current is outside the normal range, the signal transmitted by the A/F sensor will be inaccurate, as a result, the ECM will be unable to regulate air-fuel ratio properly.

5. When the current in the A/F sensor heater is outside the normal operating range, the ECM interprets this as a malfunction in the sensor heater and sets a DTC.

- Example:

- The ECM sets DTC P0032 or P0052 when the current in the A/F sensor heater fail. Conversely, when the heater current is less than 0.8 A, DTC P0031 or P0051 is set.

MONITOR STRATEGY





TYPICAL ENABLING CONDITIONS

All:





P0031 and P0051:





P0032 and P0052:





TYPICAL MALFUNCTION THRESHOLDS

P0031 and P0051:





P0032 and P0052:





COMPONENT OPERATING RANGE

P0031 and P0051:





P0032 and P0052:





CONFIRMATION DRIVING PATTERN





1. Connect the Techstream to the DLC3.

2. Turn the engine switch on (IG) and turn the Techstream on.

3. Clear the DTCs (even if no DTCs are stored, perform the clear DTC procedure) Reading and Clearing Diagnostic Trouble Codes.

4. Turn the engine switch off and wait for 30 seconds.

5. Turn the engine switch on (IG) and turn the Techstream on [A].

6. Start the engine and idle it for 5 minutes or more [B].

7. With the vehicle stationary, depress the accelerator pedal and maintain an engine speed of 3000 rpm for 1 minute [C].

8. Idle the engine for 5 minutes or more [D].

9. Enter the following menus: Powertrain / Engine / Trouble Codes.

10. Read the DTC [E].

HINT
- If a DTC is output, the system is malfunctioning.
- If a DTC is not output, perform the following procedure.

11. Enter the following menus: Powertrain / Engine / Utility / All Readiness.

12. Input the DTC: P0031, P0032, P0051 or P0052.

13. Check the DTC judgment result.





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 sows INCOMPLETE or UNKNOWN, perform steps [B] through [D] again.

14. Enter the following menus: Powertrain / Engine / Utility / All Readiness.

15. Check the DTC judgment result.

16. If the test result is INCOMPLETE or UNKNOWN and no DTC is output, perform a universal trip and check for permanent DTCs Reading and Clearing Diagnostic Trouble Codes.

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

WIRING DIAGRAM

Refer to DTC P2195 P2195.

INSPECTION PROCEDURE

HINT
- 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.
- Read freeze frame data using the Techstream. The ECM records vehicle and driving condition information as freeze frame data the moment a DTC is stored. When troubleshooting, freeze frame data can be helpful in determining whether the vehicle was running or stopped, whether the engine was warmed up or not, whether the air fuel ratio was lean or rich, as well as other data recorded at the time of a malfunction.

PROCEDURE

1. INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)

(a) Disconnect the A/F sensor connector.





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

Standard resistance (Bank 1 Sensor 1):





Standard resistance (Bank 2 Sensor 1):





(c) Reconnect the A/F sensor connector.

NG -- REPLACE AIR FUEL RATIO SENSOR Components
OK -- Continue to next step.

2. CHECK TERMINAL VOLTAGE (+B OF A/F SENSOR)

(a) Disconnect the A/F sensor connector.





(b) Turn the engine switch on (IG).

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

Standard voltage (Bank 1 Sensor 1):





Standard voltage (Bank 2 Sensor 1):





(d) Reconnect the A/F sensor connector.

NG -- INSPECT A/F FUSE
OK -- Continue to next step.

3. CHECK HARNESS AND CONNECTOR (A/F SENSOR - ECM)

(a) Disconnect the A/F sensor connector.

(b) Disconnect the ECM connector.

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

Standard resistance (Check for Open):





Standard resistance (Check for Short):





(d) Reconnect the A/F sensor connector.

(e) Reconnect the ECM connector.

NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR

OK -- REPLACE ECM Components

4. INSPECT A/F FUSE

(a) Remove the A/F fuse from the engine room No. 2 relay block.





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

Standard Resistance:





(c) Reinstall the fuse.

NG -- CHECK FOR SHORT IN ALL HARNESSES AND CONNECTORS CONNECTED TO FUSE AND REPLACE FUSE
OK -- Continue to next step.

5. INSPECT EFI NO. 2 FUSE

(a) Remove the EFI NO. 2 fuse from the engine room No. 2 relay block.





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

Standard Resistance:





(c) Reinstall the fuse.

NG -- CHECK FOR SHORT IN ALL HARNESSES AND CONNECTORS CONNECTED TO FUSE AND REPLACE FUSE
OK -- Continue to next step.

6. INSPECT A/F RELAY

(a) Remove the A/F relay from the engine room No. 2 relay block.





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

Standard Resistance:





(c) Reinstall the relay.

NG -- REPLACE A/F RELAY
OK -- Continue to next step.

7. CHECK HARNESS AND CONNECTOR (EFI MAIN RELAY - A/F RELAY)

(a) Remove the A/F relay from the engine room No. 2 relay block.





(b) Turn the engine switch on (IG).

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

Standard Voltage:





(d) Reinstall the A/F relay.

NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR (EFI MAIN RELAY - A/F RELAY)
OK -- Continue to next step.

8. CHECK HARNESS AND CONNECTOR (A/F RELAY - BODY GROUND)

(a) Remove the A/F relay from the engine room No. 2 relay block.

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

Standard Resistance (Check for Open):





(c) Reinstall the A/F relay.

NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR (A/F RELAY - BODY GROUND)

OK -- REPAIR OR REPLACE HARNESS OR CONNECTOR (BATTERY - A/F RELAY)