P0031

2ZR-FE ENGINE CONTROL SYSTEM: SFI SYSTEM: P0031, P0032: 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

The A/F sensor generates a 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 the narrow 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 into a voltage inside the ECM. Any measurements taken at the A/F sensor or ECM connectors will show a constant voltage.





HINT:
- When either of these DTCs is set, the ECM enters fail-safe mode. The ECM turns off the Air Fuel Ratio (A/F) sensor heater in fail-safe mode. Fail-safe mode continues until the ignition switch is turned to OFF.
- Although the DTC titles say the oxygen sensor, these DTCs relate to the 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 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:
- 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

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.
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.
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.
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 becomes inaccurate, as a result, the ECM is unable to regulate air-fuel ratio properly.
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.

MONITOR STRATEGY





TYPICAL ENABLING CONDITIONS

All:





P0031:





P0032:





TYPICAL MALFUNCTION THRESHOLDS

P0031:





P0032:





COMPONENT OPERATING RANGE





WIRING DIAGRAM






INSPECTION PROCEDURE
HINT: Read freeze frame data using a Techstream. Freeze frame data records 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.

PROCEDURE

1. INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)




(a) Disconnect the air fuel ratio sensor connector.
(b) Measure the resistance according to the value(s) in the table below.
Standard resistance:





(c) Reconnect the air fuel ratio sensor connector.
NG -- REPLACE AIR FUEL RATIO SENSOR
OK -- Continue to next step.
2. CHECK TERMINAL VOLTAGE (POWER SOURCE)




(a) Disconnect the air fuel ratio sensor connector.
(b) Turn the ignition switch to ON.
(c) Measure the voltage according to the value(s) in the table below.
Standard voltage:





(d) Reconnect the air fuel ratio sensor connector.
NG -- CHECK HARNESS AND CONNECTOR (AIR FUEL RATIO SENSOR - INTEGRATION RELAY)
OK -- Continue to next step.
3. CHECK HARNESS AND CONNECTOR (AIR FUEL RATIO SENSOR - ECM)




(a) Disconnect the air fuel ratio 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 air fuel ratio sensor connector.
(e) Reconnect the ECM connector.
NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR
OK -- Continue to next step.
4. CHECK WHETHER DTC OUTPUT RECURS (DTC P0031 OR P0032)
(a) Connect a Techstream to the DLC3.
(b) Turn the ignition switch to ON.
(c) Turn the tester ON.
(d) Clear DTCs DTC Check / Clear.
(e) Start the engine.
(f) Allow the engine to idle for 1 minute or more.
(g) Select the following menu items: Powertrain / Engine and ECT / Trouble Codes.
(h) Read DTCs.
Result:






B -- REPLACE ECM
A -- CHECK FOR INTERMITTENT PROBLEMS
5. CHECK HARNESS AND CONNECTOR (AIR FUEL RATIO SENSOR - INTEGRATION RELAY)




(a) Disconnect the air fuel ratio sensor connector.
(b) Remove the integration relay (EFI relay) from the engine room relay block Removal.
(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 air fuel ratio sensor connector.
(e) Reinstall the integration relay.
NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR
OK -- REPAIR OR REPLACE ECM POWER SOURCE CIRCUIT