1998 TOYOTA LAND CRUISER Factory Repair Manual

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Page 1193 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
DI-144
- DIAGNOSTICSENGINE
337 Author: Date:
2004 LAND CRUISER (RM1071U)
2 Chec

Page 1194 of 3115

TOYOTA LAND CRUISER 1998 Factory Repair Manual A21543
1
23
4 EFI or ECD Relay
A21341
+B
OX
E1HT
H6
H8
Components Side:
Bank1 Sensor2, Bank2 Sensor2
A21340
OX2B
HT1BE6
ECM ConnectorOX1B
HT2B
- DIAGNOSTICSENGINE
DI-145
338 Author: Date:
2004 LAND

Page 1195 of 3115

TOYOTA LAND CRUISER 1998 Factory Repair Manual A21040
Reference (Bank 1 Sensor 1 System Drawing)
From
BatteryEFI or ECD
No. 1 FuseEFI or ECD
RelayEFI or ECD
No. 2 FuseHeater Oxygen
Sensor
Heater
SensorHT1A
OX1A
E2
MRELECM
DI-146
- DIAGNOSTICSENGI

Page 1196 of 3115

TOYOTA LAND CRUISER 1998 Factory Repair Manual - DIAGNOSTICSENGINE
DI-147
340 Author: Date:
2004 LAND CRUISER (RM1071U)
DTC P0171 System too Lean (Bank 1)
DTC P0172 System too Rich (Bank 1)
DTC P0174 System too Lean (Bank 2)
DTC P0175 System t

- DIAGNOSTICSENGINE
DI-147
340 Author: Date:
2004 LAND CRUISER (RM1071U)
DTC P0171 System too Lean (Bank 1)
DTC P0172 System too Rich (Bank 1)
DTC P0174 System too Lean (Bank 2)
DTC P0175 System too Rich (Bank 2)
CIRCUIT DESCRIPTION
The fuel trim is related to the feedback compensation value, not to the basic injection time. The fuel trim in-
cludes the short-term fuel trim and the long-term fuel trim.
The short-term fuel trim is the short-term fuel compensation used to maintain the air-fuel ratio at stoichio-
metric air-fuel ratio. The signal from the heated oxygen sensor indicates whether the air-fuel ratio is RICH
or LEAN compared to the stoichiometric air-fuel ratio. This variance triggers a reduction in the fuel volume
if the air-fuel ratio is RICH, and an increase in the fuel volume if it is LEAN.
The long-term fuel trim is the overall fuel compensation carried out in long-term to compensate for a continu-
al deviation of the short-term fuel trim from the central value, due to individual engine differences, wear over-
time and changes in the operating environment.
If both the short-term fuel trim and the long-term fuel trim are LEAN or RICH beyond a certain value, it is
detected as a malfunction and the MIL is illuminated and a DTC is set.
DTC No.DTC Detecting ConditionTrouble Area
P0171
P0174When air-fuel ratio feedback is stable after warming up engine,
fuel trim is considerably in error on LEAN side
(2 trip detection logic)
Air induction system
Injector blockage
Mass air flow meter
Engine coolant temperature sensor
Fuel pressure
Gas leakage in exhaust system
Open or short in heated oxygen sensor (bank 1, 2 sensor 1)
circuit
Heated oxygen sensor (bank 1, 2 sensor 1)
Heated oxygen sensor heater (bank 1, 2 sensor 1)
EFI or ECD relay
PCV piping
ECM
P0172
P0175When air-fuel ratio feedback is stable after warming up engine,
fuel trim is considerably in error on RICH side
(2 trip detection logic)
Injector leak, blockage
Mass air flow meter
Engine coolant temperature sensor
Ignition system
Fuel pressure
Gas leakage in exhaust system
Open or short in heated oxygen sensor (bank 1, 2 sensor 1)
circuit
Heated oxygen sensor (bank 1, 2 sensor 1)
ECM
DIC2A-01

Page 1197 of 3115

TOYOTA LAND CRUISER 1998 Factory Repair Manual A20489A21204
Fuel compensation
amount1.40
1.0
0.65+40 (%): Thershold at LEAN
-35 (%): Thershold at RICH DI-148
- DIAGNOSTICSENGINE
341 Author: Date:
2004 LAND CRUISER (RM1071U)
HINT:
When DTC P0

Page 1198 of 3115

TOYOTA LAND CRUISER 1998 Factory Repair Manual - DIAGNOSTICSENGINE
DI-149
342 Author: Date:
2004 LAND CRUISER (RM1071U)
MONITOR STRATEGY
P0171Fuel system lean (Bank 1)
RltdDTCP0172Fuel system rich (Bank 1)Related DTCsP0174Fuel system lean (Ban

Page 1199 of 3115

TOYOTA LAND CRUISER 1998 Factory Repair Manual +25 %
-12.5 %
More than 0.5 V
Less than 0.4 V
Case 1
Case 2
Case 3
Case 4
Output voltage of heated oxygen
sensor (sensor 1: front sensor)
Injection volume
Output voltage
Output voltage of heated oxyg

+25 %
-12.5 %
More than 0.5 V
Less than 0.4 V
Case 1
Case 2
Case 3
Case 4
Output voltage of heated oxygen
sensor (sensor 1: front sensor)
Injection volume
Output voltage
Output voltage of heated oxygen
sensor (sensor 2: rear sensor)Mainly suspect
trouble area
OK
+25 %
-12.5 %
More than 0.5 V
Less than 0.4 V
Injection volume
Output voltage
+25 %
-12.5 %
More than 0.5 V
Less than 0.4 V
Injection volume
Output voltage
Sensor 1: front sensor
(sensor 1, heater, sensor 1
circuit)
+25 %
-12.5 %
More than 0.5 V
Less than 0.4 V
Injection volume
Output voltage
+25 %
-12.5 %
Injection volume
Output voltage
NG
+25 %
-12.5 %
Injection volume
Output voltage
NG
+25 %
-12.5 %
Injection volume
Output voltage
NG
+25 %
-12.5 %
Injection volume
Output voltage
NGExtremely rich or lean of the
actual air-fuel ratio
(Injector, fuel pressure, gas
leakage in exhaust system,
etc.) OK
OK
OK
Almost no reaction
'
Sensor 2: rear sensor
(sensor 2, heater, sensor 2
circuit)
Almost no reactionAlmost no reaction
Almost no reaction
DI-150
- DIAGNOSTICSENGINE
343 Author: Date:
2004 LAND CRUISER (RM1071U)
INSPECTION PROCEDURE
HINT:
Hand-held tester only:
The narrowing down the trouble area is possible by performing ACTIVE TEST of the following ºA/F CON-
TROLº (Heated oxygen sensor or another can be distinguished).
(a) Perform ACTIVE TEST by hand-held tester (A/F CONTROL).
HINT:
ºA/F CONTROLº is the ACTIVE TEST which changes the injection volume to -12.5 % or +25 %.
(1) Connect the hand-held tester to the DLC3 on the vehicle.
(2) Turn the ignition switch ON.
(3) Warm up the engine with the engine speed at 2,500 rpm for approximately 90 seconds.
(4) Select the item ºDIAGNOSIS / ENHANCED OBD II / ACTIVE TEST / A/F CONTROLº.
(5) Perform ºA/F CONTROLº with the engine in an idle condition (press the right or left button).
RESULT:
Heated oxygen sensor reacts in accordance with increase and decrease of injection volume
+25 % " rich output: More than 0.5 V
-12.5 % " lean output: Less than 0.4 V
NOTICE:
However, there is a few seconds delay in the sensor 1 (front sensor) output. And there is about 20
seconds delay in the sensor 2 (rear sensor).

Page 1200 of 3115

TOYOTA LAND CRUISER 1998 Factory Repair Manual - DIAGNOSTICSENGINE
DI-151
344 Author: Date:
2004 LAND CRUISER (RM1071U)
The following A/F CONTROL procedure enables the technician to check and graph the voltage output of
the heated oxygen senso

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