2001 TOYOTA PRIUS O2 sensor

DI±18
± DIAGNOSTICSENGINE
2001 PRIUS (RM778U)P1455
(DI±140)
Vapor Reducing Fuel Tank Sys-
tem Leak Detected (Small Leak)
Hose and pipe
Heated oxygen sensor
Fuel system
VVT system
Ignition system
Mass air flow meter
ECM

P1525
(DI±141)Resolver Circuit
MalfunctionHV ECU
Engine ECU±
P1600
(DI±143)ECM BATT MalfunctionOpen in back up power source circuit
ECM
P1633
(DI±145)ECU Malfunction (ETCS Circuit)ECM
P1636
(DI±146)HV ECU MalfunctionHV ECU
Engine ECU
P1637
(DI±148)EGSTP Signal MalfunctionHV ECU
Engine ECU±
P1656
(DI±150)OCV Circuit Malfunction (for
VVT±i)Open or short in OCV circuit
OCV
ECM

P3190
(DI±153)Poor Engine Power
Air induction system
Throttle body
Fuel pressure
Engine
Mass air flow meter

P3191
(DI±153)Engine dose not start
Mass air flow meter
Out of fuel
Engine coolant temp. sensor
Crankshaft position sensor
Camshaft position sensor
ECM
*1: 


MIL lights up

DI6UV±03
A06106
B+
Temparature Sensor
Power Transister
Platinum Hot wire
B
Output A
Voltage
FI6929
S05741
± DIAGNOSTICSENGINE
DI±23
2001 PRIUS (RM778U)
CIRCUIT INSPECTION
DTC P0100 Mass Air Flow Circuit Malfunction
CIRCUIT DESCRIPTION
The mass air flow meter uses a platinum hot wire. The hot wire air flow meter consists of a platinum hot wire,
temparature sensor and a control circuit installed in a plastic housing. The hot wire air flow meter works on
the principle that the hot wire and temparature sensor located in the intake air bypass of the housing detect
any changes in the intake air temp.
The hot wire is maintained at the set temp. by controlling the current flow through the hot wire. This current
flow is then measured as the output voltage of the air flow meter.
The circuit is constructed so that the platinum hot wire and temparature sensor provide a bridge circuit,with
the power transistor controlled so that the potential of A and B remains equal to maintain the set temp.
DTC No.DTC Detecting ConditionTrouble Area
P0100Open or short in mass air flow meter circuit with more than 3
sec. engine speed 3,000 rpm or less
Open or short in mass air flow meter circuit

Mass air flow meter

ECM
If the ECM detects DTC ºP0100º it operates the fail±safe function, keeping the ignition timing and injection
volume constant and making it possible to drive the vehicle.
HINT:
After confirming DTC P0100 use the OBD II scan tool or TOYOTA hand±held tester to confirm the mass air
flow ratio from ºCURRENT DATAº.
Mass Air Flow Value (gm/sec.)Malfunction
0.0
Mass air flow meter power source circuit open

VG circuit open or short
271.0 or more
E2G circuit open

FI4741
(fig.1)
Acceptable
Resistance kW
± 20 0 20 40 60 80 100
(± 4) 32 68 104 140 176 212 30
20
10
5
3
2
1
0.5
0.3
0.2
0.1
Te m p .°C (F°)
DI±28
± DIAGNOSTICSENGINE
2001 PRIUS (RM778U)
DTC P0110 Intake Air Temp. Circuit Malfunction
CIRCUIT DESCRIPTION
The intake air temp. sensor is built into the mass air flow meter
and senses the intake air temperature.
A thermistor built in the sensor changes the resistance value
according to the intake air temperature, the lower the intake air
temperature, the greater the thermistor resistance value, and
the higher the intake air temperature, the lower the thermistor
resistance value (See fig.1).
The air intake temperature sensor is connected to the ECM
(See below). The 5V power source voltage in the ECM is ap-
plied to the intake air temp. sensor from the terminal THA via
a resistor R.
That is, the resistor R and the intake air temp. sensor are con-
nected in series. When the resistance value of the intake air
temp. sensor changes in accordance with changes in the intake
air temperature, the potential at terminal THA also changes.
Based on this signal, the ECM increases the fuel injection vol-
ume to improve driveability during cold engine operation.
If the ECM detects the DTC ºP0110º, it operates the fail safe
function in which the intake air temperature is assumed to be
20°C (68°F).
DTC No.DTC Detecting ConditionTrouble Area
P0110Open or short in intake air temp. sensor circuit

Open or short in intake air temp. sensor circuit

Intake air temp. sensor (built into mass air flow meter)

ECM
HINT:
After confirming DTC P0110, use the OBD II scan tool or TOYOTA hand±held tester to confirm the intake
air temperature from CURRENT DATA.
Temperature DisplayedMalfunction
±40°C (±40°F)Open circuit
140°C (284°F) or moreShort circuit
DI6UX±02

A00310
E8
E822
18ECM
5V
THA
E2
E1 R
R±B
BR 4
5 (Built into mass air flow meter)M1
Intake Air Temp. Sensor
± DIAGNOSTICSENGINE
DI±29
2001 PRIUS (RM778U)
WIRING DIAGRAM
INSPECTION PROCEDURE
HINT:

If DTC P0110 , P0115 and P0120 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 warmed up or not, the air±fuel
ratio lean or rich, etc. at the time of the malfunction.
1 Connect OBD II scan tool or TOYOTA hand±held tester, and read value of intake
air temperature.
PREPARATION:
(a) Connect the OBD II scan tool or TOYOTA hand±held tester to DLC3.
(b) Turn the ignition switch ON and push the OBD II scan tool or TOYOTA hand±held tester main switch
ON.
CHECK:
Read temperature value on the OBD II scan tool or TOYOTA hand±held tester.
OK:
Same as actual air intake temperature.
HINT:

If there is open circuit, OBD II scan tool or TOYOTA hand±held tester indicates ± 40°C (± 40°F).

If there is short circuit, OBD II scan tool or TOYOTA hand-held tester indicates 140°C (284°F) or more.
NG ±40°C (±40°F) ....Go to step 2.
140°C (284°F) or more ....Go to step 4.
OK
Check for intermittent problems
(See page DI±3).

BE6653
A00347
A00348
ON
ECM
Intake Air
Temp. Sensor
4
5
Connecting
BE6653
A13620A00360A13621
ON
Intake Air
Temp. Sensor
54
THAE2
ECM
5 V
E2THA
E1 3
9
DI±30
± DIAGNOSTICSENGINE
2001 PRIUS (RM778U)
2 Check for open in harness or ECM.
PREPARATION:
(a) Disconnect the intake temp. sensor connector.
(b) Connect sensor wire harness terminals together.
(c) Turn the ignition switch ON.
CHECK:
Read temp. value on the OBD II scan tool or TOYOTA
hand±held tester.
OK:
Temp. value: 140°C (284°F) or more
OK Confirm good connection at sensor. If OK,
replace intake air temp. sensor.
NG
3 Check for open in harness or ECM.
PREPARATION:
(a) Remove the ECM with connector still connected (See
page SF±62).
(b) Connect between terminals THA and E2 of the ECM con-
nector.
HINT:
In take air temp. sensor connector is disconnected.
Before checking, do a visual and contact pressure check for the
ECM connector (See page IN±41).
(c) Turn the ignition switch ON.
CHECK:
Read temperature value on the OBD II scan tool or TOYOTA
hand±held tester.
OK:
Temperature value: 140°C (284°F) or more
OK Open in harness between terminals E2 or THA,
repair or replace harness.
NG
Confirm good connection at ECM. If OK,
check and replace ECM (See page IN±41).

BE6653
A00362A00363
ON
Intake Air
Temp. SensorECM
4
5
A09085A09091
ON
Intake Air Temp.
Sensor
E8 Connector
ECM
5 V
E2THA
E1
± DIAGNOSTICSENGINE
DI±31
2001 PRIUS (RM778U)
4 Check for short in harness and ECM.
PREPARATION:
(a) Disconnect the mass air flow meter connector.
(b) Turn the ignition switch ON.
CHECK:
Read temperature value on the OBD II scan tool or TOYOTA
hand±held tester.
OK:
Temperature value: ±40°C (±40°F)
OK Replace mass air flow meter.
NG
5 Check for short in harness or ECM.
PREPARATION:
(a) Remove the ECM with connector still connected (See
page SF±62).
(b) Disconnect the E8 connector of the ECM.
HINT:
Intake air temp. sensor connector is disconnected.
(c) Turn the ignition switch ON.
CHECK:
Read temperature value on the OBD II scan tool or TOYOTA
hand±held tester.
OK:
Temperature value: ±40°C (±40°F)
OK Repair or replace harness or connector.
NG
Check and replace ECM (See page IN±41).

A00310
E1
Engine Coolant Temp.
Sensor
2
1ECM
W
BR14
E8
E8185V
THW
E2
E1 R DI±32
± DIAGNOSTICSENGINE
2001 PRIUS (RM778U)
DTC P0115 Engine Coolant Temp. Circuit Malfunction
CIRCUIT DESCRIPTION
A thermistor built into the engine coolant temp. sensor changes the resistance value according to the engine
coolant temp.
The structure of the sensor and connection to the ECM is the same as in the intake air temp. circuit malfunc-
tion shown on page DI±28.
If the ECM detects the DTC P0115, it operates fail safe function in which the engine coolant temperature
is assumed to be 80°C (176°F).
DTC No.Detection ItemTrouble Area
P0115Open or short in engine coolant temp. sensor circuit

Open or short in engine coolant temp. sensor circuit

Engine coolant temp. sensor

ECM
HINT:
After confirming DTC P0115, use the OBD II scan tool or TOYOTA hand±held tester to confirm the engine
coolant temp. from ºCURRENT DATAº.
Temp. DisplayedMalfunction
±40°C (±40°F)Open circuit
140°C (284°F) or moreShort circuit
WIRING DIAGRAM
INSPECTION PROCEDURE
HINT:

If DTC P0110, P0115 and P0120 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 warmed up or not, the air±fuel
ratio lean or rich, etc. at the time of the malfunction.
DI6UY±02

BE6653
A00365
A00366
ON
ECM
2
1 Water Temp. Sensor
Connecting
± DIAGNOSTICSENGINE
DI±33
2001 PRIUS (RM778U)
1 Connect OBD II scan tool or TOYOTA hand±held tester, and read value of
engine coolant temperature.
PREPARATION:
(a) Connect the OBD II scan tool or TOYOTA hand±held tester 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 temperature value on the OBD II scan tool or TOYOTA hand±held tester.
OK:
Same as actual engine coolant temperature
HINT:

If there is open circuit, OBD II scan tool or TOYOTA hand±held tester indicates ±40°C (±40°F).

If there is open circuit, OBD II scan tool or TOYOTA hand-held tester indicates 140°C (284°F) or more.
NG ±40°C (±40°F) ... Go to step 2.
140°C (284°F) or more ... Go to step 4.
OK
Check for intermittent problems
(See page DI±3).
2 Check for open in harness or ECM.
PREPARATION:
(a) Disconnect the engine coolant temp. sensor connector.
(b) Connect the sensor wire harness terminals together.
(c) Turn the ignition switch ON.
CHECK:
Read temperature value on the OBD II scan tool or TOYOTA
hand±held tester.
OK:
Temperature value: 140°C (284°F) or more
OK Confirm good connection at sensor. If OK,
replace engine coolant temp. sensor.
NG