P0031

2GR-FE ENGINE CONTROL SYSTEM: SFI SYSTEM: 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)

DTC P0051 - Oxygen (A/F) Sensor Heater Control Circuit Low (Bank 2 Sensor 1)

DTC P0052 - Oxygen (A/F) Sensor Heater Control Circuit High (Bank 2 Sensor 1)

CAUTION / NOTICE / HINT
HINT:
- Although the DTC titles say the 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.

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 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.
A three-way catalytic converter (TWC) is used in order to convert the carbon monoxide (CO), hydro carbon (HC), and nitrogen oxides (NOx) into less harmful substances. To allow the TWC to function effectively, it is necessary to keep the air-fuel ratio of the engine near the stoichiometric air-fuel ratio.
*: 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 ignition 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 cylinder No. 1.
- Bank 2 refers to the bank that does not include cylinder No. 1.
- Sensor 1 refers to the closest sensor to the engine assembly.
- Sensor 2 refers to the furthest sensor away from the engine assembly.
- When any of these DTCs are set, check the A/F sensor voltage output by selecting the following menu items on Techstream: Powertrain / Engine and ECT / Data List / A/F Control System / AFS B1 S1 or AFS B2 S1.
- Short-term fuel trim values can also be read using Techstream.
- The ECM regulates the voltages at the A1A+, A2A+, A1A- and A2A- terminals of the ECM to a constant level. Therefore, the A/F sensor voltage output cannot be confirmed without using Techstream.
- If an A/F sensor malfunction is detected, the ECM sets a DTC.

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 gas.
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 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 will be inaccurate, as a result, the ECM will be 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.

Example:
- The ECM sets DTC P0032 or P0052 when the current in the A/F sensor heater is more than 10 A. 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

MONITOR RESULT

Refer to CHECKING MONITOR STATUS Mode 6 Data.

WIRING DIAGRAM

INSPECTION PROCEDURE
HINT: Read freeze frame data using 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 A5 or A6 A/F sensor connector.
(b) Measure the resistance according to the value(s) in the table below.
Standard resistance:
Bank 1

Bank 2

C -- REPLACE AIR FUEL RATIO SENSOR
B -- REPLACE AIR FUEL RATIO SENSOR
A -- Continue to next step.
2. CHECK TERMINAL VOLTAGE (+B OF A/F SENSOR)

(a) Disconnect the A5 or A6 A/F sensor connector.
(b) Turn the ignition switch to the ON position.
(c) Measure the voltage according to the value(s) in the table below.
Standard voltage:

(d) Reconnect the A/F sensor connector.
OK -- CHECK HARNESS AND CONNECTOR (A/F RELAY - ECM)
NG -- Continue to next step.
3. INSPECT FUSE (A/F FUSE)

(a) Remove the A/F fuse from the engine room junction block.
(b) Measure the resistance according to the value(s) in the table below.
Standard resistance:
Below 1 Ohms
(c) Reinstall the A/F fuse.
NG -- INSPECT FUSE (A/F FUSE)
OK -- Continue to next step.
4. INSPECT RELAY (A/F RELAY)

(a) Remove the A/F relay from the No. 6 engine room relay block.
(b) Measure the resistance according to the value(s) in the table below.
Standard resistance:

(c) Reinstall the A/F relay.
NG -- REPLACE RELAY (A/F RELAY)
OK -- Continue to next step.
5. CHECK HARNESS AND CONNECTOR (A/F SENSOR - A/F RELAY)

(a) Disconnect the A5 or A6 A/F sensor connector.
(b) Remove the A/F relay from the No. 6 engine room relay block.
(c) Measure the resistance according to the value(s) in the table below.
Standard resistance:
Check for open

Check for short

(d) Reinstall the A/F relay.
(e) Reconnect the A/F sensor connector.
NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR (A/F SENSOR - A/F RELAY)
OK -- Continue to next step.
6. CHECK HARNESS AND CONNECTOR (A/F RELAY - BODY GROUND)

(a) Remove the A/F relay from the No. 6 engine room relay block.
(b) Measure the resistance according to the value(s) in the table below.
Standard resistance:
Check for open

NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR (A/F RELAY - BODY GROUND)
OK -- REPAIR OR REPLACE HARNESS OR CONNECTOR (A/F RELAY - BATTERY)
7. CHECK HARNESS AND CONNECTOR (A/F RELAY - ECM)

(a) Disconnect the A5 or A6 A/F sensor connector.
(b) Disconnect the E10 ECM connector.
(c) Measure the resistance according to the value(s) in the table below.
Standard resistance:
Check for open

Check for short

(d) Reconnect the ECM connector.
(e) Reconnect the A/F sensor connectors.
NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR (A/F RELAY - ECM)
OK -- Continue to next step.
8. CHECK WHETHER DTC OUTPUT RECURS
(a) Connect Techstream to the DLC3.
(b) Turn the ignition switch to the ON position.
(c) Turn Techstream ON.
(d) Clear the 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 Code.
(h) Read the DTCs.
Result:

B -- REPLACE ECM
A -- CHECK FOR INTERMITTENT PROBLEMS