2001 TOYOTA AVALON Service Repair Manual

- DIAGNOSTICSENGINE
DI-37
193 Author
: Date
:
2001 AVALON (RM808U)
OK
Replace engine coolant temperature sensor.

P24296
ECM
Throttle Position
Sensor
VC
VTA
E2
S05019A09773
ECM
1
3
22
23
185 V
VC
VTA1
E2 L-R
LG
W Throttle Position Sensor
E5 E5 E5 DI-38
- DIAGNOSTICSENGINE
194 Author
: Date
:
2001 AVALON (RM808U)
DTC P0120 Throttle/Pedal position Sensor/Switch ºAº
Circuit Malfunction
CIRCUIT DESCRIPTION
The throttle position sensor is mounted in the throttle body and
detects the throttle valve opening angle. When the throttle valve
is fully closed, a voltage of approximately 0.7 V is applied to ter-
minal VTA of the ECM. The voltage applied to terminals VTA of
the ECM increases in proportion to the opening angle of the
throttle valve and becomes approximately 2.7 - 5.2 V when the
throttle valve is fully opened. The ECM judges the vehicle driv-
ing conditions from these signals input from terminals VTA and
uses them as one of the conditions for deciding the air-fuel ratio
correction, power increase correction and fuel-cut control etc.
DTC No.DTC Detecting ConditionTrouble Area
P0120
Condition (a) or (b) continues:
(a) VTA
0.1 V
(b) VTA
4.9 V

Open or short in throttle position sensor circuit

Throttle position sensor

ECM
HINT:
After confirming DTC P0120, use the OBD II scan tool or TOYOTA hand-held tester to confirm the throttle
valve opening percentage and closed throttle position switch condition.
Throttle valve opening position expressed as percentageTblAThrottle valve fully closedThrottle valve fully openTrouble Area
0 %0 %
VC circuit open

VTA circuit open or short
Approx. 100 %Approx. 100 %
E2 circuit open
WIRING DIAGRAM
INSPECTION PROCEDURE
HINT:

If DTCs P0110, P0115 and P0120 are output simultaneously, E2 (sensor ground) bay be open.
DI6T1-01

FI7052
A00437
1 ON
BE6653
S05338
(+)
(-)
- DIAGNOSTICSENGINE
DI-39
195 Author
: Date
:
2001 AVALON (RM808U)

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 was warmed up or not, the air-fuel
ratio was lean or rich, etc. at the time of the malfunction.
1 Connect OBD II scan tool or TOYOTA hand-held tester, and read throttle valve
opening percentage.
PREPARATION:
(a) Connect the OBD II scan tool or TOYOTA hand-held tes-
ter to the DLC3.
(b) Turn the ignition switch ON and push the OBD II scan tool
or TOYOTA hand-held tester main switch ON.
CHECK:
Read the throttle valve opening percentage.
OK:
Throttle ValveThrottle valve opening position
expressed as percentage
Fully openApprox. 75 %
Fully closedApprox. 10 %
OK Check for intermittent problems
(See page DI-3).
NG
2 Check voltage between terminal 1 of wire harness side connector and body
ground.
PREPARATION:
(a) Disconnect the throttle position sensor connector.
(b) Turn the ignition switch ON.
CHECK:
Measure the voltage between terminal 1 (VC) of the wire har-
ness side connector and body ground.
OK:
Voltage: 4.5 - 5.5 V
NG Go to step 5.
OK
3 Check throttle position sensor (See page SF-33).

A02021
ON
E2
VTA
(-) (+)
A02022
ON
VC
E2
(-) (+)
DI-40
- DIAGNOSTICSENGINE
196 Author
: Date
:
2001 AVALON (RM808U)
NG Replace throttle position sensor.
OK
4 Check voltage between terminals VTA and E2 of ECM connector.
PREPARATION:
(a) Remove the glove compartment (See page SF-82).
(b) Turn the ignition switch ON.
CHECK:
Measure the voltage between terminals VTA1 and E2 of the
ECM connector.
OK:
Throttle ValveVoltage
Fully closed0.3 - 1.0 V
Fully open2.7 - 5.2 V
NG Check for open and short in harness and con-
nector in VTA circuit between ECM and throttle
position sensor (See page IN-30).
OK
Check and replace ECM (See page IN-30).
5 Check voltage between terminals VC and E2 of ECM connector.
PREPARATION:
(a) Remove the glove compartment (See page SF-82).
(b) Turn the ignition switch ON.
CHECK:
Measure the 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-30).
OK

- DIAGNOSTICSENGINE
DI-41
197 Author
: Date
:
2001 AVALON (RM808U)
Check for open in harness and connector in
VC circuit between ECM and throttle position
sensor (See page IN-30).

DI-42
- DIAGNOSTICSENGINE
198 Author
: Date
:
2001 AVALON (RM808U)
DTC P0121 Throttle/Pedal Position Sensor/Switch ºAº
Circuit Range/Performance Problem
CIRCUIT DESCRIPTION
Refer to DTC P0120 on page DI-38.
DTC No.DTC Detecting ConditionTrouble 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)

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 was warmed up or not, the air-fuel ratio was 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 (See page DI-14).
NO
Replace throttle position sensor.
DI07L-09

A00477
Atmosphere
Cover
Exhaust GasPlatinum
Electrode
Solid Electrolyte
(Zirconia Element)
Platinum
Electrode
Heater
A/F Sensor Voltage
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
19
Housing
- DIAGNOSTICSENGINE
DI-43
199 Author
: Date
:
2001 AVALON (RM808U)
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 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 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), (c) and (d) continue for at
least 1.5 min:
*: Output value changes at inside of the 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 closed
(d) 140 sec. or more after starting engine
Open or short in A/F sensor (bank 1, 2 sensor 1) circuit

A/F sensor (bank 1, 2 sensor 1)

Air inducation system

Fuel pressure

Injector

Gas leakage on exhaust sytem

ECM
HINT:

After confirming DTC P0125, use the OBD II scan tool or TOYOTA hand-held tester to confirm voltage
output of the A/F sensor (bank 1, 2 sensor 1) from the CURRENT DATA.

The ECM controls the voltage of the AFR+, AFL+, AFR- and AFL- terminals of the ECM to the fixed
voltage. Therefore, it is impossible to confirm the A/F sensor output voltage without the OBDII scan
tool or TOYOTA hand-held tester.
DI07M-14

A11670
HTS
E03 AFR+
3.3 VECM
to Analog-Digital
Converter
to Analog-Digital
Converter
AFR-
AFL+ HAFR
3.3 V3.0 V
AFL-
OXSHAFL
3.0 VE04
E05
E1 E79
8 4
213
1220 11 E5
E5
E5
E5
E5
E5
E7
L-O
LG
B
B-R
L
B-W
BR
B-RB-R
LG
B B-W
B-W
B-W
B-W
B-W
BR
BR B From
Battery
From Terminal
MREL of ECMA/F Sensor
(Bank 1
Sensor 1)
J5 J/C
J7 J/CA/F Sensor
(Bank 2
Sensor 1)
Heated
Oxygen
Sensor
(Bank 1
Sensor 2)2
3
41
2
3
41
2
3
41 23
5
1
23
5
1 A/F Relay
EFI Relay Engine Room J/B
16
19
IK28 16
IK2 IK2II2
EC
1021
IK2
II2
EB
A
A
A12
13
9
2B
4 2B 2B2B
4 2FA/F
EFI
No.2 2
2GEFI
No.1
W-B
ED
BR
BR
BRBR B
B DI-44
- DIAGNOSTICSENGINE
200 Author
: Date
:
2001 AVALON (RM808U)

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:
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 was warmed up or not, the air-fuel ratio was lean
or rich, etc. at the time of the malfunction.