When one 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 ignition switch is turned off.

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 P0031 Oxygen (A/F) Sensor Heater Control Circuit Low (Bank 1 Sensor 1). 1GR-FE ENGINE CONTROL. Land Cruiser URJ200 URJ202 GRJ200 VDJ200

DTC No.	DTC Detection Condition	Trouble Area
P0031 P0051	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 (sensor 1) Integration relay ECM
P0032 P0052	Air fuel ratio sensor heater current failure (1 trip detection logic).	Short in air fuel ratio sensor heater circuit Air fuel ratio sensor heater (sensor 1) Integration relay ECM
P101D P103D	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 (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 the 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 ().

INSPECTION PROCEDURE

NOTICE:

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

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.

Change the fuel injection volume using the Control the Injection Volume function provided in the Active Test and monitor the air fuel ratio sensor output voltage (). If the sensor output voltage does not change (almost no reaction) while performing the Active Test, the sensor may be malfunctioning.

1.INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)

Inspect the air fuel ratio sensor ().

REPLACE AIR FUEL RATIO SENSOR ()

OK

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

Dtc P0031 Oxygen (A/F) Sensor Heater Control Circuit Low (Bank 1 Sensor 1). 1GR-FE ENGINE CONTROL. Land Cruiser URJ200 URJ202 GRJ200 VDJ200

Disconnect the air fuel ratio sensor connector.

Turn the ignition switch to ON.

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

Standard Voltage:
Tester Connection Switch Condition Specified Condition
C22-2 (+B) - Body ground Ignition switch ON 11 to 14 V
C23-2 (+B) - Body ground Ignition switch ON 11 to 14 V

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

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:

for LHD
Tester Connection	Condition	Specified Condition
C22-1 (HA1A) - C45-22 (HA1A)	Always	Below 1 Ω
C23-1 (HA2A) - C45-20 (HA2A)	Always	Below 1 Ω
C22-1 (HA1A) or C45-22 (HA1A) - Body ground	Always	10 kΩ or higher
C23-1 (HA2A) or C45-20 (HA2A) - Body ground	Always	10 kΩ or higher

for RHD
Tester Connection	Condition	Specified Condition
C22-1 (HA1A) - C46-22 (HA1A)	Always	Below 1 Ω
C23-1 (HA2A) - C46-20 (HA2A)	Always	Below 1 Ω
C22-1 (HA1A) or C46-22 (HA1A) - Body ground	Always	10 kΩ or higher
C23-1 (HA2A) or C46-20 (HA2A) - Body ground	Always	10 kΩ or higher

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

4.CHECK WHETHER DTC OUTPUT RECURS (DTC P0031, P0032, P0051, P0052, P101D OR P103D)

Connect the GTS to the DLC3.

Turn the ignition switch to ON.

Turn the GTS on.

Clear the DTCs ().

Start the engine.

Allow the engine to idle for 1 minute or more.

Read the output pending DTCs using the GTS.

Result
Result	Proceed to
No pending DTC is output	A
Pending DTC P0031, P0032, P0051, P0052, P101D or P103D is output	B

REPLACE ECM ()

CHECK FOR INTERMITTENT PROBLEMS ()

5.INSPECT INTEGRATION RELAY (A/F)

Inspect the integration relay (A/F) ().

REPLACE INTEGRATION RELAY

OK

6.CHECK HARNESS AND CONNECTOR (INTEGRATION RELAY (A/F) - A/F SENSOR AND BODY GROUND)

Disconnect the air fuel ratio sensor connector.

Remove the integration relay from the engine room relay block.

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

Standard Resistance:

Tester Connection	Condition	Specified Condition
C22-2 (+B) - 1A-4	Always	Below 1 Ω
C23-2 (+B) - 1A-4	Always	Below 1 Ω
1A-2 - 1B-4	Always	Below 1 Ω
1A-3 - Body ground	Always	Below 1 Ω
C22-2 (+B) or 1A-4 - Body ground	Always	10 kΩ or higher
C23-2 (+B) or 1A-4 - Body ground	Always	10 kΩ or higher
1A-2 or 1B-4 - Body ground	Always	10 kΩ or higher

REPAIR OR REPLACE HARNESS OR CONNECTOR

CHECK ECM POWER SOURCE CIRCUIT ()

1GR-FE ENGINE CONTROL

Land Cruiser URJ200 URJ202 GRJ200 VDJ200

SFI SYSTEM

Tester Connection	Switch Condition	Specified Condition
C22-2 (+B) - Body ground	Ignition switch ON	11 to 14 V
C23-2 (+B) - Body ground	Ignition switch ON	11 to 14 V