TOYOTA PRIUS 2001 Service Repair Manual

DI±36
± DIAGNOSTICSENGINE
2001 PRIUS (RM778U)
DTC P0116 Engine Coolant Temp. Circuit Range/
Performance Problem
CIRCUIT DESCRIPTION
Refer to DTC P0115 on page DI±32.
DTC No.DTC Detecting ConditionTrouble Area
When the engine starts, the water temp. is ±7°C (20°F) or
less. And, 20 min. or more after the engine starts, the engine
temp. sensor value is 5°C (41°F) or less (2 trip detection logic)
When the engine starts, the water temp. is between ±7°C
(20°F) and 10°C (50°F). And, 5 min. or more after the engine
starts, the engine coolant temp. sensor value is 5°C (41°F) or
less. (2 trip detection logic)
P0116When the fluctuations in the engine coolant tempeerature are
within 3 °C (37 °F)before and afrer the follwing conditions are
met:
1. IDL OFF time  250 sec.
2. Vehicle speed change of 30 km/h (19 mph) or more occurs
10 times or more.
3. 35 °C (95 °F)
Engine coolant temperature when the
ignition switch is turned ON < 60 °C (140 °F)
4. Intake air temperature after starting the engine  ±6.7 °C
(20 °F)
Engine coolant temp. sensor

Cooling system
INSPECTION PROCEDURE
HINT:

If DTC P0115 and P0116 are output simultaneously, engine coolant temp. sensor circuit may be open.
Perform troubleshooting of DTC P0115 first.

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 P0116) being output?
YES Go to relevant DTC chart.
NO
DI6UZ±03

± DIAGNOSTICSENGINE
DI±37
2001 PRIUS (RM778U)
2 Check thermostat (See page CO±9).
NG Replace thermostat.
OK
Replace engine coolant temp. sensor.

A02396 A02395A02624
Throttle Position Sensor
Output Voltage (V)0 1.5
Accelerator Pedal Opening Angle (deg)70 125
VTA VTA2
5
VTA2 VTA E2 VCMovable Range
Usable RangeUsable Range *1*2
*1
*2
Movable Range
Usable
Range
*2
*1
Throttle valve
fully closed
Throttle valve
fully open *
2: *
1:
VTA2 circuit open or ground short
Accelerator pedal opening position expressed as percentage and voltage
Accelerator pedal releasedAccelerator pedal depressed
THROTTLE POS THROTTLE POS #2THROTTLE POS THROTTLE POS #2
0 %
0 %
100 % 8 ± 20 %0 V
2.0 ± 2.9 V
0 V
5 V0 %
0 %
100 %0 V
4.6 ± 5.1 V
0 V
5 VTrouble area
VC circuit open
VTA circuit open or ground short
E2 circuit open 64 ± 96 %
DI±38
± DIAGNOSTICSENGINE
2001 PRIUS (RM778U)
DTC P0120 Throttle/Pedal Position Sensor/Switch ºAº
Circuit Malfunction
CIRCUIT DESCRIPTION
Throttle position sensor is mounted on the throttle body and it have the 2 sensors to detect the throttle open-
ing angle and the malfunction of the throttle position sensor's own.
The voltage applied to the terminals VTA and VTA2 of the ECM changes between 0 V and 5 V in proportion
to the opening angle of the throttle valve.
The ECM judges the current opening angle of the throttle valve from these signals input from terminals VTA
and VTA2, and the ECM controls the throttle motor to make the throttle valve angle properly in response to
driving condition.
If this DTC is stored, the ECM shuts down the power for the throttle motor, and the throttle valve is fully closed
by the return spring.
DTC No.DTC Detecting ConditionTrouble Area
P0120
Condition (a), (b), (c), (d) or (e) continues for 2.0 seconds:
(a) VTA
0.2 V
(b) VTA2
0.625 V
(c) VTA  4.8 V
(d) When VTA  0.2 V and
2.0 V, and VTA2  4.97 V
(e) VTA ± VTA2
0.02 V

Open or short in throttle position sensor circuit

Throttle position sensor

ECM
Condition (a) continues for 0.4 seconds:
(a) VTA
0.2 V and VTA2
0.5 V
HINT:
After confirming DTC P0120, use the OBD II scan tool or TOYOTA hand±held tester to confirm the accelera-
tor pedal opening position percentage.
DI2DQ±07

A14051
T3
Throttle Position
SensorECM
2 3
PL E2
VC Y±R
BR232
21 18
VTA VC
VTA2 E2 E8
E8 E8
E8 (Shielded)
EB AJ9
J/C A J8
J/C
4 1 CC
BR
VTA2
VTA1 Y±R
FI7052
± DIAGNOSTICSENGINE
DI±39
2001 PRIUS (RM778U)
WIRING DIAGRAM
INSPECTION PROCEDURE
HINT:

If DTCs P0110, P0115, P0120, P0450 and P1120 are output simultaneously, E2 (sensor ground) may
be open.

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.
LEXUS hand±held tester:
1 Connect LEXUS hand±held tester, and read throttle valve opening percentage.
PREPARATION:
(a) Connect the TOYOTA hand±held tester to the DLC3.
(b) Turn the ignition switch ON and push the TOYOTA hand±
held tester main switch ON.
CHECK:
Read the throttle valve opening percentage for VTA circuit and
read the voltage for VTA2 circuit.

A13624
ON
E2 VC
(+)
(±)
A13625
ON
VTAVTA2
E2
(+)
(±)
DI±40
± DIAGNOSTICSENGINE
2001 PRIUS (RM778U)
OK:
Accelerator Pedal
Throttle valve opening
position expressed
as percentage (VTA)
Voltage (VTA2)
Released64 ± 96 %4.6 ± 5.1 V
Depressed8 ± 20 %2.0 ± 2.9 V
OK Check and replace ECM (See page IN±41).
NG
2 Check voltage between terminals VC and E2 of ECM connector.
PREPARATION:
(a) Remove the ECM with connector still connected (See
page SF±62).
(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±41).
OK
3 Check voltage between terminals VTA and E2, and VTA2 and E2 of ECM connec-
tor.
PREPARATION:
(a) Remove the ECM with connector still connected (See
page SF±62).
(b) Turn the ignition switch ON.
CHECK:
Measure the voltage between terminals VTA and E2, and VTA2
and E2 of the ECM connector.
OK:
Alt dlVoltageAccelerator pedalVTA ± E2VTA2 ± E2
Released0.4 ± 1.0 V2.0 ± 2.9 V
Depressed3.2 ± 4.8 V4.6 ± 5.1 V

A13624
ON
E2 VC
(+)
(±)
± DIAGNOSTICSENGINE
DI±41
2001 PRIUS (RM778U)
OK Check and replace ECM (See page IN±41).
NG
4 Check throttle position sensor (See page SF±24).
NG Replace throttle position sensor
(See page SF±29).
OK
Check for open and short in harness and connector in VC, VTA, VTA2 and E2 circuits between
ECM and throttle position sensor (See page IN±41).
OBD II scan tool (excluding TOYOTA hand±held tester):
1 Check voltage between terminals VC and E2 of ECM connector.
PREPARATION:
(a) Remove the ECM with connector still connected (See
page SF±62).
(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±41).
OK

A13625
ON
VTAVTA2
E2
(+)
(±)
DI±42
± DIAGNOSTICSENGINE
2001 PRIUS (RM778U)
2 Check voltage between terminals VTA and E2, and VTA2 and E2 of ECM connec-
tor.
PREPARATION:
(a) Remove the ECM with connector still connected (See
page SF±62).
(b) Turn the ignition switch ON.
CHECK:
Measure the voltage between terminals VTA and E2, and VTA2
and E2 of the ECM connector.
OK:
Alt dlVoltageAccelerator pedalVTA ± E2VTA2 ± E2
Released0.4 ± 1.0 V2.0 ± 2.9 V
Depressed3.2 ± 4.8 V4.6 ± 5.1 V
OK Check and replace ECM (See page IN±41).
NG
3 Check throttle position sensor (See page SF±24).
NG Replace throttle position sensor
(See page SF±29).
OK
Check for open and short in harness and connector in VC, VTA, VTA2 and E2 circuits between
ECM and throttle position sensor (See page IN±41).

P21242 FI7210
A04485
Atmosphere
Flange
Platinum Electrode
Solid Electrolyte
(Zirconia Element)
Platinum Electrode
Heater
Coating (Ceramic)
Exhaust Gas CoverIdeal Air±Fuel Mixture
Output Voltage
Richer ± Air Fuel Ratio ± Leaner
DI±44
± DIAGNOSTICSENGINE
2001 PRIUS (RM778U)
DTC P0125 Insufficient 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 oxygen sensor has the characteristic whereby its output voltage changes suddenly in the vicinity of the
stoichiometric air±fuel ratio. This is used to detect the oxygen concentration in the exhaust gas and provide
feedback to the computer for control of the air±fuel ratio.
When the air±fuel ratio becomes LEAN, the oxygen concentration in the exhaust increases and the oxygen
sensor informs the ECM of the LEAN condition (small electromotive force: < 0.45 V).
When the air±fuel ratio is RICHER than the stoichiometric air±fuel ratio the oxygen concentration in the ex-
haust gas in reduced and the oxygen sensor informs the ECM of the RICH condition (large electromotive
force: > 0.45V).
The ECM judges by the electromotive force from the oxygen sensor whether the air±fuel ratio is RICH or
LEAN and controls the injection time accordingly. However, if malfunction of the oxygen sensor causes out-
put of abnormal electromotive force, the ECM is unable to perform accurate air±fuel ratio control.
The 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 temp. of the exhaust gas is low) current flows to the heater to heat
the sensor for accurate oxygen concentration detection.
DTC No.DTC Detecting ConditionTrouble Area
P0125
After the engine is warmed up, oxygen sensor (bank 1 sensor
1) output does not indicate RICH (
0.45 V) even once when
conditions (a), (b), and (c) continue for at least 50 sec.
(a) Engine speed: 800 rpm or more
(b) Vehicle speed: 40 ± 100 km/h (25 ± 62 mph)
(c) 20 sec. or more after starting engine

Fuel system

Air induction system

Injector

Ignition system

Gas leakage on exhaust system

Open or short in heated oxygen sensor (bank 1 sensor 1)
circuit

Heated oxygen sensor (bank 1 sensor 1)

ECM
DI6V2±03

A14052
ECM
G±R
7
236 1B1AIA2 12
BR
G±Y 1
1 EFI2
1 5
11
1 1
12
3 Engine Room J/B
B±GF12
MAINFL
Block
No. 2
BatteryJ1
J/C W±B4
B
P±L
Y12
2
4 3
A
IEB
IP1BR
J23 BR
H9
Bank 1
Sensor 22
1 4
3
18
E10
E10E2 MREL
E11
BR IE1
IE1
IE1 W
W
D
11 2225
16
7 (Shielded) (Shielded)(Shielded) 2
FL Block No. 1
F13
J7
J/CJ4
J/C
J/C
A
ACHT1A
OX1B E10E10 E10E8E9
OX1A
HT1B G±R
EFI
Relay
1K 1F
1F
C
B
J23 J22 J23E
E EBR BR IK1
IK1
IK1 W (Shielded)P±L
P±L H3
Bank 1
Sensor 1
B
B
W±B 3
13
12
± DIAGNOSTICSENGINE
DI±45
2001 PRIUS (RM778U)
HINT:
After confirming DTC P0125, use the OBD II scan tool or TOYOTA hand-held tester to confirm voltage output
of oxygen sensor (bank 1 sensor 1) from "CURRENT DATA".
If voltage output of oxygen sensor (bank 1 sensor 1) is less than 0.1 V, oxygen sensor (bank 1 sensor 1) circuit
may be open or short.
WIRING DIAGRAM

DI±46
± DIAGNOSTICSENGINE
2001 PRIUS (RM778U)
INSPECTION PROCEDURE
HINT:

If the vehicle run out of 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.

There is a possibility that P0125 is detected because of abnormal fuel system, so, when P0125 is mem-
orized, check P0171 and P0172 even if P0171 and P0172 are memorized.
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 oxygen sensor (bank 1 sensor 1).
PREPARATION:
(a) Connect the OBD II scan tool or TOYOTA hand±held tester to the DLC3.
(b) Warm up engine to normal operating temp (above 75°C).
CHECK:
Read voltage output of the oxygen sensor (bank 1 sensor 1) when engine is suddenly raced.
HINT:
Perform quick racing to 4,000 rpm 3 times using accelerator pedal.
OK:
Both oxygen sensor (bank 1 sensor 1) output a RICH signal (0.45 V or more) at least once.
OK Go to step 9.
NG
3 Check for open and short in harness and connector between ECM and oxygen
sensor (bank 1 sensor 1) (See page IN±41).
NG Repair or replace harness or connector.
OK