1Gr-Fe Engine Control. Dtc P0031 Oxygen (A/F) Sensor Heater Control Circuit Low (Bank 1 Sensor 1)

When any 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. The ECM continues operating in fail-safe mode until the engine switch is turned off.
Although the DTC titles say heated 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 (TWC) and located near the engine assembly.

The ECM provides a pulse-width modulated control circuit 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 P0051	The air fuel ratio sensor heater current is below 0.8 A (1 trip detection logic).	Open in air fuel ratio sensor heater circuit Air fuel ratio sensor heater (for bank 1, 2 sensor 1) No. 1 integration relay (A/F) ECM
P0032 P0052	An air fuel ratio sensor heater current failure (1 trip detection logic).	Short in air fuel ratio sensor heater circuit Air fuel ratio sensor heater (for bank 1, 2 sensor 1) No. 1 integration relay (A/F) ECM
P101D P103D	The heater current is higher than a specified value while the heater is not operating (1 trip detection logic).	Short in air fuel ratio sensor heater circuit ECM

HINT:

Bank 1 refers to the bank that includes the No. 1 cylinder.
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.

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 (TWC) 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.

WIRING DIAGRAM

Refer to DTC P2195 (LandCruiser RM000000WC40YDX_07.html).

INSPECTION PROCEDURE

HINT:

Read freeze frame data using the GTS. 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.

1.INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)

Inspect the air fuel ratio sensor (LandCruiser RM000002RV202KX_01_0001.html).
HINT:
for Automatic Transmission
Perform "Inspection After Repair" after replacing the air fuel ratio sensor (LandCruiser RM000004NJC03SX.html).

REPLACE AIR FUEL RATIO SENSOR (LandCruiser RM000002W9Q017X.html)

OK

2.CHECK TERMINAL VOLTAGE (+B OF AIR FUEL RATIO SENSOR)

Land Cruiser, Land Cruiser Prado. Grj150 Trj150,155 Kdj150,155 Lj150, Gdj150,155.1Gr-Fe Engine Control.Sfi System.
Dtc
P0031 Oxygen (A/F) Sensor Heater Control Circuit Low (Bank 1 Sensor 1)

Disconnect the air fuel ratio sensor connector.

Measure the voltage according to the value(s) in the table below.
Standard Voltage:
Tester Connection
Switch Condition
Specified Condition
C25-2 (+B) - Body ground
Engine switch on (IG)
11 to 14 V
C26-2 (+B) - Body ground
Engine switch on (IG)
11 to 14 V
Text in Illustration
*A
Bank 1
*B
Bank 2
*a
Front view of wire harness connector
(to Air Fuel Ratio Sensor)

Text in Illustration
*A	Bank 1
*B	Bank 2
*a	Front view of wire harness connector (to Air Fuel Ratio Sensor)

Reconnect the air fuel ratio sensor connector.

Go to step 5

OK

3.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 (Check for Open):

for Automatic Transmission
Tester Connection	Condition	Specified Condition
C25-1 (HA1A) - C37-17 (HA1A)	Always	Below 1 Ω
C26-1 (HA2A) - C37-12 (HA2A)	Always	Below 1 Ω

for Manual Transmission
Tester Connection	Condition	Specified Condition
C25-1 (HA1A) - C37-17 (HA1A)	Always	Below 1 Ω
C26-1 (HA2A) - C37-19 (HA2A)	Always	Below 1 Ω

Standard Resistance (Check for Short):

for Automatic Transmission
Tester Connection	Condition	Specified Condition
C25-1 (HA1A) or C37-17 (HA1A) - Body ground	Always	10 kΩ or higher
C26-1 (HA2A) or C37-12 (HA2A) - Body ground	Always	10 kΩ or higher

for Manual Transmission
Tester Connection	Condition	Specified Condition
C25-1 (HA1A) or C37-17 (HA1A) - Body ground	Always	10 kΩ or higher
C26-1 (HA2A) or C37-19 (HA2A) - Body ground	Always	10 kΩ or higher

Reconnect the air fuel ratio sensor connector.

Reconnect the ECM connector.

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

4.CHECK WHETHER DTC OUTPUT RECURS

Connect the GTS to the DLC3.

Turn the engine switch on (IG).

Turn the GTS on.

Clear the DTCs (LandCruiser RM000000PDK1DIX.html).

Start the engine.

Allow the engine to idle for 1 minute or more.

Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.

Read the DTCs.

Result
Result	Proceed to
No output	A
P0031, P0032, P0051, P0052, P101D or P103D	B

REPLACE ECM (LandCruiser RM00000329203TX.html)

CHECK FOR INTERMITTENT PROBLEMS (LandCruiser RM000000PDQ18TX.html)

5.INSPECT NO. 1 INTEGRATION RELAY (A/F)

Inspect the air fuel ratio sensor relay (LandCruiser RM000003BLB03QX_01_0015.html).

REPLACE NO. 1 INTEGRATION RELAY (A/F)

OK

6.CHECK HARNESS AND CONNECTOR (AIR FUEL RATIO SENSOR - NO. 1 INTEGRATION RELAY (A/F))

Disconnect the air fuel ratio sensor connector.

Remove the No. 1 integration relay from the engine room relay block.

Measure the resistance according to the value(s) in the table below.
Standard Resistance (Check for Open):
Tester Connection
Condition
Specified Condition
C25-2 (+B) - 1B-8
Always
Below 1 Ω
C26-2 (+B) - 1B-8
Always
Below 1 Ω
Standard Resistance (Check for Short):
Tester Connection
Condition
Specified Condition
C25-2 (+B) or 1B-8 - Body ground
Always
10 kΩ or higher
C26-2 (+B) or 1B-8 - Body ground
Always
10 kΩ or higher

Reconnect the air fuel ratio sensor connector.

Reinstall the No. 1 integration relay.

REPAIR OR REPLACE HARNESS OR CONNECTOR

CHECK ECM POWER SOURCE CIRCUIT (LandCruiser RM000001DN80BOX.html)

Tester Connection	Switch Condition	Specified Condition
C25-2 (+B) - Body ground	Engine switch on (IG)	11 to 14 V
C26-2 (+B) - Body ground	Engine switch on (IG)	11 to 14 V