Service Manuals, User Guides, Schematic Diagrams or docs for : . Car Manuals Toyota Sienna 1998-2003 Approved FSM 05 eg cip0125
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DI-42
DIAGNOSTICS - ENGINE
DI4F0-02
DTC P0125 Insufficient Coolant Temp. for Closed Loop
Fuel Control
CIRCUIT DESCRIPTION
To obtain a high purification rate for the CO, HC and NOx components of the exhaust gas, a three-way
catalytic 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 A/F sensor has the characteristic that provides output voltage* approximately proportional to the existing
air-fuel ratio. The A/F sensor output voltage* is used to provide feedback for the ECM to control the air-fuel
ratio.
By the A/F sensor output, the ECM can determine the deviation amount from the stoichiometric air-fuel ratio
and control the proper injection time immediately. If the A/F sensor is malfunctioning, ECM is unable to per-
form accurate air-fuel ratio control.
The A/F sensor is equipped with a heater which heats the zirconia element. The heater is controlled by the
ECM. When the intake air volume is low (the temp. of the exhaust gas is low), current flows to the heater
to heat the sensor for accurate oxygen concentration detection.
*: The voltage value changes at the inside of the ECM only.
Atmosphere
(V)
Platinum 4.0
A/F Sensor Voltage
Electrode 3.8
3.6
ECM Monitored
Solid Electrolyte
(Zirconia Element) 3.4
3.2
Platinum 3.0
Electrode 2.8
2.6
Heater
2.4
Coating (Ceramic)
12 13 14 15 16 17 18 19
Air-Fuel Ratio
Cover Exhaust Gas
A00477
DTC No. DTC Detecting Condition Trouble Area
After engine is warmed up, A/F sensor output* does not
S Fuel system
change when conditions (a), (b) and (c) continue for at least
S Injector
1.5 min.
S Ignition system
*: Output value changes at inside of ECM only.
P0125 S Gas leakage on exhaust system
(a) Engine speed: 1,500 rpm or more
S Open or short in A/F sensor circuit (bank 1, 2 sensor 1)
(b) Vehicle speed: 40 - 100 km/h (25 - 62 mph)
S A/F sensors (bank 1, 2 sensor 1)
(c) Throttle valve does not fully closed
S ECM
(d) After starting engine y 140 sec
HINT:
S After confirming DTC P0125, use the OBD II scan tool or TOYOTA hand-held tester to confirm voltage
output of heated oxygen sensors (bank 1, 2 sensor 1) from CURRENT DATA.
S The ECM controls the voltage of AF and AF terminals of ECM to the fixed voltage. Therefore, it
is impossible to confirm the A/F sensor output voltage without OBD II scan tool or TOYOTA hand-held
tester.
2001 SIENNA (RM787U)
Author : Date : 196
DI-43
DIAGNOSTICS - ENGINE
S OBD II scan tool (excluding TOYOTA hand-held tester) displays the one fifth of the A/F sensor output
voltage which is displayed on the TOYOTA hand-held tester.
WIRING DIAGRAM
E04
E05
to Analog-Digital
to Analog-Digital
E03
Converter
Converter
B+
ECM
E1
4 HAFL
8 MREL
AFR+
3 HAFR
20 AFR-
3.3 V
12 AFL+
3.0 V
3.3 V
3.0 V
8 OXS
21 AFL-
HTS
E11
E11
E11
E11
E11
E9
E8
E11
11
E9
9
BR
B-R
L-W
W
R
L
L
B-W
4
3
B
2
20
II2
II2
1
9
Y-G
Heated Oxygen sensor
A/F sensor
4
(Bank 1, Sensor 1)
3
(Bank1, Sensor 2)
C
W
L-W
C
B
J13
J/C
2
1
J14
A BR J/C
C
A/F sensor
(Bank 2, Sensor 1)
A B-R
BR BR
3
B-R
B-R
B-R
4
2 IH1
B
EC
II2
2 3A
11 3B
II2
19
2
1
1
IH1
8
Y-G
J/B No.3
Engine Room J/B No.2
2 2J 7 2K 9 2J
L-R
W-B
EFI Relay
5 2C
EE
L
2
1
EFI
W
3 2B
2
3
5
B-L
2A
1
IJ
Battery
5
3
W-B
MAIN
L
L-B
FL
A/F HTR
L
IK5
1
1
2
1
2
1
10
* USA 15A Canada 20A A/F HTR Relay
Engine Room R/B No.1 A07521
INSPECTION PROCEDURE
HINT:
Read freeze frame data using TOYOTA hand-held tester or OBD II scan tool. Because freeze frame records
the engine conditions when the malfunction is detected, when troubleshooting it is useful for determining
whether the vehicle was running or stopped, the engine warmed up or not, the air-fuel ratio lean or rich, etc.
at the time of the malfunction.
2001 SIENNA (RM787U)
Author : Date : 197
DI-44
DIAGNOSTICS - ENGINE
1 Are there any other codes (besides DTC P0125) being output ?
YES Go to relevant DTC chart.
NO
2 Connect the OBD II scan tool or TOYOTA hand-held tester and read value for
voltage output of A/F sensors (bank 1, 2 sensor 1).
PREPARATION:
(a) Connect the OBD II scan tool or TOYOTA hand-held tester to the DLC3.
(b) Warm up the A/F sensors (bank 1, 2 sensor 1) with the engine at 2,500 rpm for approx. 90 sec.
CHECK:
Read voltage value of A/F sensors (bank 1, 2 sensor 1) on the screen of OBD II scan tool or TOYOTA hand-
held tester when you perform all the following conditions.
HINT:
The voltage of AFR ,AFL terminal of ECM is 3.3 fixed and the AFR ,AFL terminal is 3.0 V fixed.
Therefore, it is impossible to check the A/F sensor output voltage at the terminals (AFR ,AFL /
AFR ,AFL ) of ECM.
OK:
Condition A/F Sensor Voltage value
Engine idling
S N t remains at 3.3. V (*0.660 V)
Not i t 3 3 (*0 660
( 0.660
Engine idli
E i idling
S Not remains at 3 8 V (*0.76 V) or more
3.8 (*0 76
Driving at engine speed 1,500 rpm or more and vehicle S Not remains at 2.8 V (*0.56 V) or less
speed 40 km/h (25 mph) or move, and operate throttle valve
*: When you use the OBD II scan tool (excluding TOYOTA hand-held tester)
open and close
HINT:
S During fuel enrichment, there is a case that the output voltage of A/F sensors (bank 1, 2 sensor 1) is
below 2.8 V (* 0.56 V), it is normal.
S During fuel cut, there is a case that the output voltage of A/F sensors (bank 1, 2 sensor 1) is above
3.8 V (* 0.76 V), it is normal.
S If output voltage of A/F sensors (bank 1, 2 sensor 1) remains at 3.30 V (* 0.660 V) even after performing
all the above conditions, A/F sensors (bank 1, 2 sensor 1) circuit may be open.
S If output voltage of A/F sensor remains at 3.8 V (* 0.76 V) or more, or 2.8 V (* 0.56 V) or less even after
performing all the above conditions, A/F sensors (bank 1, 2 sensor 1) circuit may be short.
*: When you use the OBD II scan tool (excluding TOYOTA hand-held tester).
OK Go to step 10.
NG
2001 SIENNA (RM787U)
Author : Date : 198
DI-45
DIAGNOSTICS - ENGINE
3 Check for open and short in harness and connector between ECM and A/F
sensors (bank1, 2 sensor1) (See page IN-31 ).
NG Repair or replace harness or connector.
OK
4 Check resistance of A/F sensor heaters (bank1, 2 sensor1) (See page SF-81 ).
NG Replace A/F sensor.
OK
5 Check air induction system (See page SF-1 ).
NG Repair or replace.
OK
6 Check fuel pressure (See page SF-6 ).
NG Check and repair fuel pump, fuel pipe line and
filter (See page SF-1 ).
OK
7 Check injector injection (See page SF-26 ).
NG Replace injector.
OK
2001 SIENNA (RM787U)
Author : Date : 199
DI-46
DIAGNOSTICS - ENGINE
8 Check gas leakage on exhaust system.
NG Repair or replace
OK
Replace A/F sensors (bank1, 2 sensor1).
9 Perform confirmation driving pattern (See page DI-104 ).
Go
10 Is there DTC P0125 being output again ?
YES Check and replace ECM
(See page IN-31 ).
NO
11 Did vehicle runs out of fuel in the past ?
NO Check for intermittent problems
(See page DI-3 ).
YES
DTC P0125 is caused by running out of fuel.
2001 SIENNA (RM787U)
Author : Date : 200
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