Page 2473 of 4770
A03008A03414
ON
VC
(+) E2
(±)
w/o Immobiliser
w/ Immobiliser
VC
(+) E2
(±)
± DIAGNOSTICSENGINE (5S±FE)
DI±53
288 Author: Date:
5 Check voltage between terminals VC and E2 of ECM connector.
PREPARATION:
(a) Remove the glove compartment (See page SF±64).
(b) Turn ignition switch ON.
CHECK:
Measure voltage between terminals VC and E2 of the ECM
connector.
OK:
Voltage: 4.5 ~ 5.5 V
NG Check and replace ECM (See page IN±31).
OK
Check for open in harness and connector be-
tween ECM and sensor (VC line)
(See page IN±31).
Page 2474 of 4770

DI±54
± DIAGNOSTICSENGINE (5S±FE)
289 Author: Date:
DTC P0121 Throttle/Pedal Position Sensor/Switch ºAº
Circuit Range/Performance Problem
CIRCUIT DESCRIPTION
Refer to DTC P0120 (Throttle/Pedal Position Sensor/Switch "A" Circuit Malfunction) on page DI±49.
DTC No.Detection ItemTrouble Area
P0121
After vehicle speed has been exceeded 30 km/h (19 mph)
even once, output value of throttle position sensor is out of
applicable range while vehicle speed between 30 km/h (19
mph) and 0 km/h (0 mph)
(2 trip detection logic)
Throttle position sensor
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.
1 Are there any other codes (besides DTC P0121) being output?
YES Go to relevant DTC chart.
NO
Replace throttle position sensor.
DI00S±04
Page 2475 of 4770

A00477
Atmosphere
Cover
Exhaust GasPlatinum
Electrode
Solid Electrolyte
(Zirconia Element)
Platinum
Electrode
Heater
Air±Fuel Ratio
(V)
2.6 4.0
3.8
3.6
3.4
3.2
3.0
2.8
2.4
12 13 14 15 16 17 18
Coating (Ceramic)
ECM Monitored
A/F Sensor Voltage
19
± DIAGNOSTICSENGINE (5S±FE)
DI±55
290 Author: Date:
DTC P0125 Insufficient Coolant Temp. for Closed Loop
Fuel Control (Only for California Spec.)
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 exist-
ing 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.
DTC No.DTC Detecting ConditionTrouble Area
P0125
After engine is warmed up, A/F sensor output* does not
change when conditions (a), (b), and (c) continue for at least
1.5 min.:
*: Output value changes at inside of ECM only
(a) Engine speed: 1,500 rpm or more
(b) Vehicle speed: 40 ~ 100 km/h (25 ~ 62 mph)
(c) Throttle valve is not fully closedFuel system
Injector
Ignition system
Gas leakage on exhaust system
Open or short in A/F sensor circuit
A/F sensor
ECM
DI1JU±03
Page 2476 of 4770

A03597
B±Y
FL
Block47
EFI
IGN
14 2
4 EFI
Relay
21
53
B±Y
BR
3
12 B
B
1
24 3 9
II3
J/CB
W±R
P±B
W
BG
P±B 56
2
5
1K
14
HT2 21 O 1W
E9E8
E9 E8
MAIN FLE8 1B
B 1ECMAF
OX2 HTAF
AF 1K
2F
E03 E1E04 A/F
Sensor
Engine Room R/B No.2
B±YJ19 J/C
2
1
II2II3
II3
EB
Heated
Oxygen
Sensor
(Bank 1
Sensor 2)
EC
Instrument
Panel J/B7
3 5
6
7
2L 2A
F611
F4
B±G
Battery B±R
2K
2J
W±B
3.3V
3.0V
AM2 B
W±R
J27
*1: w/o Immobiliser
*2: w/ Immobiliser
(*1)
(*2)
to Analog±Digital
Converter
E914 E8 13
(*1) (*2) J27
B±Y
B±Y
IG Switch
B±R
*3: California
(*6) (*3) (*6) (*3)
(*1)
2
MREL
E107
(*2)
EE
J27 J27
J/C
B BB±Y
II4
6
B±W(*2)
B±W(*2)
*5:TMC Made
*6:TMMK Made
L(*5)
(*3)
B±W(*5)
(*3)
BR
*4: Except California
DI±56
± DIAGNOSTICSENGINE (5S±FE)
291 Author: Date:
HINT:
After confirming DTC P0125, use the OBD II scan tool or TOYOTA hand-held tester to confirm voltage
output of A/F sensor from the CURRENT DATA.
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.
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
INSPECTION PROCEDURE
HINT:
If the vehicle run out fuel, the air±fuel ratio is LEAN and DTC P0125 will be recorded.
The MIL then comes on.
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.
Page 2477 of 4770

± DIAGNOSTICSENGINE (5S±FE)
DI±57
292 Author: Date:
1 Are there any other codes (besides DTC P0125) being output?
YES Go to relevant DTC chart.
NO
2 Connect OBD II scan tool or TOYOTA hand±held tester, and read value for volt-
age output of A/F sensor.
PREPARATION:
(a) Connect the OBD II scan tool or TOYOTA hand±held tester to the DLC3.
(b) Warm up the A/F sensor with the engine at 2,500 rpm for approx. 90 sec.
CHECK:
Read voltage value of the A/F sensor on the screen of OBD II scan tool or TOYOTA hand±held tester when
you perform all the following conditions.
HINT:
The voltage of AF terminal of ECM is 3.3 V fixed and the A/F terminal is 3.0 V fixed. Therefore, it is impos-
sible to check the A/F sensor output voltage at the terminals (AF/AF) of ECM.
OK:
ConditionA/F Sensor Voltage Value
Engine idling
Engine racing Not remains at 3.30 V (* 0.660 V)
Not remains at38V(*076V)ormoreDriving at engine speed 1,500 rpm or more and vehicle
speed 40 km/h (25 mph) or more, and operate throttle valve
open and close Not remains at 3.8 V (* 0.76 V) or more
Not remains at 2.8 V (* 0.56 V) or less
*: When you use the OBD II scan tool (excluding TOYOTA hand±held tester)
HINT:
During fuel enrichment, there is a case that the output voltage of the A/F sensor is below 2.8 V (* 0.56
V), it is normal.
During fuel cut, there is a case that the output voltage of the A/F sensor is above 3.8 V (* 0.76 V), it
is normal.
If output voltage of the A/F sensor remains at 3.30 V (* 0.660 V) even after performing all the above
conditions, A/F the sensor circuit may be open.
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 sensor circuit may be short.
*: When you use the OBD II scan tool (excluding TOYOTA hand±held tester).
OK Go to step 10.
NG
Page 2478 of 4770
DI±58
± DIAGNOSTICSENGINE (5S±FE)
293 Author: Date:
3 Check for open and short in harness and connector between ECM and A/F sen-
sor (See page IN±31).
NG Repair or replace harness or connector.
OK
4 Check resistance of A/F sensor heater (See page SF±59).
NG Replace A/F sensor.
OK
5 Check air induction system (See page SF±1).
NG Replace or replace.
OK
6 Check EGR system (See page EC±12).
NG Repair EGR system.
OK
7 Check fuel pressure (See page SF±6).
NG Check and repair fuel pump, fuel pipe line and
filter (See page SF±1).
OK
Page 2479 of 4770
± DIAGNOSTICSENGINE (5S±FE)
DI±59
294 Author: Date:
8 Check injector injection (See page SF±23).
NG Replace injector.
OK
9 Check gas leakage on exhaust system.
NG Repair or replace.
OK
Replace A/F sensor.
10 Perform confirmation driving pattern (See page DI±152).
Go
11 Is there DTC P0125 being output again?
YES Check and replace ECM.
NO
Page 2480 of 4770
DI±60
± DIAGNOSTICSENGINE (5S±FE)
295 Author: Date:
12 Did vehicle runs out of fuel in the past?
NO Check for intermittent problems.
YES
DTC P0125 is caused by running out of fuel.