P0031, P0032, P101D

DTC Code	DTC Name
P0031	Oxygen (A/F) Sensor Heater Control Circuit Low (Bank 1 Sensor 1)
P0032	Oxygen (A/F) Sensor Heater Control Circuit High (Bank 1 Sensor 1)
P101D	A/F Sensor Heater Circuit Performance Bank 1 Sensor 1 Stuck ON

DESCRIPTION

Refer to DTC P2195 Click here.

Tech Tips

When either of these DTCs is stored , the ECM enters fail-safe mode. The ECM turns off the air fuel ratio sensor heater in fail-safe mode. Fail-safe mode continues until the power switch is turned off.
Although the DTC titles say the oxygen sensor, these DTCs relate to the air fuel ratio sensor.
Sensor 1 refers to the sensor mounted in front of the Three-way catalytic converter and located near the engine assembly.
The ECM uses pulse width modulation to adjust the current through the heater. The air fuel ratio sensor heater circuit uses a relay on the +B side of the circuit.

DTC No.	DTC Detection Condition	Trouble Area
P0031	Air fuel ratio sensor heater current is below 0.8 A, even when the air fuel ratio sensor heater duty cycle is 30% or more (1 trip detection logic).	Open in air fuel ratio sensor (sensor 1) heater circuit Air fuel ratio sensor (sensor 1) ECM
P0032	An air fuel ratio sensor heater current reaches the high limit (Hybrid IC high current limiter port "Fail") (1 trip detection logic).	Short in air fuel ratio sensor (sensor 1) heater circuit Air fuel ratio sensor (sensor 1) ECM
P101D	The heater current is higher than the specified value while the heater is not operating (1 trip detection logic).	ECM

MONITOR DESCRIPTION

The ECM uses information from the air fuel ratio 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 to purify the exhaust gases.

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

When the current in the air fuel ratio sensor heater is outside the normal operating range, the ECM interprets this as a malfunction in the sensor heater and stores a DTC.

MONITOR STRATEGY

Frequency of Operation

Continuous

TYPICAL ENABLING CONDITIONS

P0031
Air fuel ratio sensor heater output duty cycle	30% or more

P0032
Air fuel ratio sensor heater duty cycle	More than 0%

P101D
Air fuel ratio sensor heater duty cycle	10% or more, and less than 60%
Air fuel ratio sensor heater ON current	0.8 A or higher

CONFIRMATION DRIVING PATTERN

Connect the intelligent tester to the DLC3.
Turn the power switch on (IG) and turn the tester on.
Clear the DTCs (even if no DTCs are stored, perform the clear DTC operation).
Turn the power switch off and wait for at least 30 seconds.
Turn the power switch on (IG) and turn the tester on [A].
Put the engine in inspection mode (maintenance mode) Click here.
Start the engine and idle it for 5 minutes or more [B].
With the vehicle stationary, depress the accelerator pedal and maintain an engine speed of 2500 rpm for 1 minute [C].

Tech Tips

During charging control, the engine speed is set at idle. Therefore, the engine speed does not increase when depressing the accelerator pedal. In this case, perform steps [C] and [D] after charging control has completed.
Idle the engine for 5 minutes or more [D].
Enter the following menus: Powertrain / Engine and ECT / DTC.
Read the pending DTCs [E].
Tech Tips
- If a pending DTC is output, the system is malfunctioning.
- If a pending DTC is not output, perform the following procedure.
Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.
Input the DTC: P0031, P0032 or P101D.

Check the DTC judgment result.

Tester Display	Description
NORMAL	DTC judgment completed System normal
ABNORMAL	DTC judgment completed System abnormal
INCOMPLETE	DTC judgment not completed Perform driving pattern after confirming DTC enabling conditions
N/A	Unable to perform DTC judgment Number of DTCs which do not fulfill DTC preconditions has reached ECU memory limit

Tech Tips

If the judgment result shows NORMAL, the system is normal.
If the judgment result shows ABNORMAL, the system has a malfunction.
If the judgment result shows INCOMPLETE or N/A, perform steps [B] through [E] again.

WIRING DIAGRAM

Refer to DTC P2195 Click here.

INSPECTION PROCEDURE

Note

Inspect the fuses for circuits related to this system before performing the following inspection procedure.

Tech Tips

Refer to "Data List / Active Test" [A/F Heater Duty #1] Click here.
Read freeze frame data using the intelligent tester. The ECM records vehicle and driving condition information as freeze frame data the moment a DTC is stored. 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.
Sensor 1 refers to the sensor closest to the engine assembly.
Sensor 2 refers to the sensor farthest away from the engine assembly.
Change the fuel injection volume using the Control the Injection Volume for A/F Sensor function provided in the Active Test and monitor the air fuel ratio sensor output voltage Click here. If the sensor output voltage does not change (almost no reaction) while performing the Active Test, the sensor may be malfunctioning.

PROCEDURE

INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)
1. Inspect the air fuel ratio sensor Click here.
NG
REPLACE AIR FUEL RATIO SENSOR Click here

OK

CHECK TERMINAL VOLTAGE (POWER SOURCE OF AIR FUEL RATIO SENSOR)

Text in Illustration

*a
Front view of wire harness connector

(to Air Fuel Ratio Sensor (Sensor 1))

Disconnect the air fuel ratio sensor connector.
Turn the power switch on (IG).

Text in Illustration
*a	Front view of wire harness connector (to Air Fuel Ratio Sensor (Sensor 1))

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

Standard Voltage

Tester Connection	Condition	Specified Condition
D23-2 (+B) - Body ground	Power switch on (IG)	11 to 14 V

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR (AIR FUEL RATIO SENSOR - EFI MAIN RELAY)

OK

CHECK HARNESS AND CONNECTOR (AIR FUEL RATIO SENSOR - ECM)

Disconnect the air fuel ratio sensor connector.
Disconnect the ECM connector.

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

Standard Resistance

Tester Connection	Condition	Specified Condition
D23-1 (HA1A) - D27-18 (HA1A)	Always	Below 1 Ω
D23-1 (HA1A) or D27-18 (HA1A) - Body ground	Always	10 kΩ or higher

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

CHECK WHETHER DTC OUTPUT RECURS (DTC P0031, P0032 OR P101D)

Connect the intelligent tester to the DLC3.
Turn the power switch on (IG).
Turn the tester on.
Clear the DTCs Click here.
Drive the vehicle in accordance with the driving pattern described in the Confirmation Driving Pattern.
Enter the following menus: Powertrain / Engine and ECT / DTC.

Read the DTCs.

Result
Result	Proceed to
DTC is not output	A
DTC P0031, P0032 or P101D is output	B

B

REPLACE ECM Click here

A

CHECK FOR INTERMITTENT PROBLEMS Click here

SFI SYSTEM (w/o EGR System), Diagnostic DTC:P0031, P0032, P101D