1998 TOYOTA LAND CRUISER Factory Repair Manual

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Page 1097 of 3115

TOYOTA LAND CRUISER 1998 Factory Repair Manual - DIAGNOSTICSENGINE
DI-357
550 Author: Date:
2004 LAND CRUISER (RM1071U)
3 Check that MIL lights up.
Check that MIL lights up when turning the ignition switch ON.
Standard: MIL lights up
OK System

Page 1098 of 3115

TOYOTA LAND CRUISER 1998 Factory Repair Manual DIC22-01
- DIAGNOSTICSENGINE
DI-49
242 Author: Date:
CIRCUIT INSPECTION
DTC P0031 Oxygen Sensor Heater Control Circuit Low
(Bank 1 Sensor 1)
DTC P0032 Oxygen Sensor Heater Control Circuit High
(Bank

Page 1099 of 3115

TOYOTA LAND CRUISER 1998 Factory Repair Manual P20302
FI7210
A00798
Atmosphere
Housing
Platinum Electrode
Solid Electrolyte
(Zirconia Element)
Platinum Electrode
Heater
Coating (Ceramic)
Exhaust Gas CoverIdeal Air-Fuel Mixture
Output Voltage
Riche

P20302
FI7210
A00798
Atmosphere
Housing
Platinum Electrode
Solid Electrolyte
(Zirconia Element)
Platinum Electrode
Heater
Coating (Ceramic)
Exhaust Gas CoverIdeal Air-Fuel Mixture
Output Voltage
Richer - Air Fuel Ratio - Leaner
A21040
Reference(Bank 1 Sensor 1 System Drawing) :
ECM
EFI or ECD Relay
EFI or ECD
Fuse No. 1 From
Battery
GroundOX1A
MREL HT1A
Duty
Control Heater
Sensor Heated Oxygen Sensor
EFI or ECD
Fuse No. 2
E2 DI-50
- DIAGNOSTICSENGINE
243 Author: Date:
CIRCUIT DESCRIPTION
To obtain a high purification rate for the CO, HC and NOx components of the exhaust gas, a three-way cata-
lytic converter is used, but for the most efficient use of the three-way catalytic converter, the air-fuel ratio
must be precisely controlled so that it is always close to the stoichiometric air-fuel ratio.
The heated oxygen sensor has the characteristic which its output voltage changes suddenly in the vicinity
of the stoichiometric air-fuel ratio. This characteristic is used to detect the oxygen concentration in the ex-
haust gas and provide the ECM with feedback to control the air-fuel ratio.
When the air-fuel ratio becomes LEAN, the oxygen concentration in the exhaust increases and the heated
oxygen sensor informs the ECM of the LEAN condition (low voltage, i.e. less than 0.45 V).
When the air-fuel ratio is RICHER than the stoichiometric air-fuel ratio, the oxygen concentration in the ex-
haust gas is reduced and the heated oxygen sensor informs the ECM of the RICH condition (high voltage,
i.e. more than 0.45 V). The ECM judges by the voltage output from the heated oxygen sensor whether the
air-fuel ratio is RICH or LEAN and controls the injection time accordingly. However, if malfunction of the
heated oxygen sensor causes output of abnormal voltage, this disables the ECM for performing an accurate
air-fuel ratio control. The heated oxygen sensors include a heater which heats the zirconia element. The
heater is controlled by the ECM. When the intake air volume is low (the temperature of the exhaust gas is
low) current flows to the heater to heat the sensor for accurate oxygen concentration detection.
HINT:
The ECM provides a pulse width modulated control circuit to adjust current through the heater. The heated
oxygen sensor heater circuit uses a relay on the B+ side of the circuit.

Page 1100 of 3115

TOYOTA LAND CRUISER 1998 Factory Repair Manual - DIAGNOSTICSENGINE
DI-51
244 Author: Date:
DTC No.DTC Detecting ConditionTrouble Area
P0031
P0037
Heater current is 0.25 A or less when the heater operates with
Open in heater circuit of heated ox

Page 1101 of 3115

TOYOTA LAND CRUISER 1998 Factory Repair Manual DI-52
- DIAGNOSTICSENGINE
245 Author: Date:
MONITOR STRATEGY
P0031Heated oxygen sensor heater current bank 1
sensor 1 (Low current)
P0032Heated oxygen sensor heater current bank 1
sensor 1 (High cur

Page 1102 of 3115

TOYOTA LAND CRUISER 1998 Factory Repair Manual - DIAGNOSTICSENGINE
DI-53
246 Author: Date:
TYPICAL MALFUNCTION THRESHOLDS
Detection CriteriaThreshold
P0031, P0037, P0051, P0057 (Low current):
Heated oxygen sensor heater currentLess than 0.25 A (

Page 1103 of 3115

TOYOTA LAND CRUISER 1998 Factory Repair Manual A21367
ECM
MREL
E2
HT2A
OX2A
OX1A HT1A
HT2B
OX2B
OX1B HT1B 8
28
33
22
234
25
21
295 E9
E5
E6
E6
E6E6
E6
E6
E6 E6 J/B No. 5
2 15
5C
5D B-W
1
1 1
1
12
3 4 Engine Room R/B
EFI or ECD Relay
W-B
B-Y
B-Y
B-

Page 1104 of 3115

TOYOTA LAND CRUISER 1998 Factory Repair Manual A20870
E1 +B
OX
+BHT
OX E1HT H5
H7
H6
H8
Components Side:
Bank1 Sensor1, Bank2 Sensor1
Bank1 Sensor2, Bank2 Sensor2
- DIAGNOSTICSENGINE
DI-55
248 Author: Date:
INSPECTION PROCEDURE
HINT:
Read freez

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