2001 TOYOTA PRIUS coolant

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

± DIAGNOSTICSENGINE
DI±61
2001 PRIUS (RM778U)
DTC P0171 System too Lean (Fuel Trim)
DTC P0172 System too Rich (Fuel Trim)
CIRCUIT DESCRIPTION
Fuel trim refers to the feedback compensation value compared against the basic injection time. Fuel trim
includes short±term fuel trim and long±term fuel trim.
Short±term fuel trim is the short±term fuel compensation used to maintain the air±fuel ratio at its ideal
theoretical value. The signal from the oxygen sensor indicates whether the air±fuel ratio is RICH or LEAN
compared to the ideal theoretical value, triggering a reduction in fuel volume if the air±fuel ratio is rich, and
an increase in fuel volume if it is lean.
Long±term fuel trim is overall fuel compensation carried out long±term to compensate for continual deviation
of the short±term fuel trim from the central value due to individual engine differences, wear over time and
changes in the usage environment.
If both the short±term fuel trim and long±term fuel trim are LEAN or RICH beyond a certain value, it is
detected as a malfunction and the MIL lights up.
DTC No.DTC Detecting ConditionTrouble Area
P0171
When the air±fuel ratio feedback is stable after engine warming
up, the fuel trim is considerably in error on the RICH side
(2 trip detection logic)

Air induction system

Injector blockage

Mass air flow meter

Engine coolant temp. sensor

Fuel pressure

Gas leakage on exhaust system

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

Heated oxygen sensor (bank 1 sensor 1)
P0172
When air fuel ratio feedback is stable after warming up engine,
the fuel trim is considerably in error on LEAN side (2 trip detec-
tion logic)

Injector leak, blockage

Mass air flow meter

Engine coolant temp. sensor

Ignition system

Fuel pressure

Gas leakage on exhaust system

Open or short in heated oxygen sensor (bank 1, 2 sensor 1)
circuit

Heated oxygen sensor (bank 1, 2 sensor 1)

ECM
HINT:

When DTC P0171 is recorded, the actual air±fuel ratio is on the LEAN side. When DTC P0172 is re-
corded, the actual air±fuel ratio is on the RICH side.

If the vehicle runs out of fuel, the air±fuel ratio is LEAN and DTC P0171 is recorded. The MIL then
comes on.

If the total of the short±term fuel trim value and long±term fuel trim value is within + 38 %, the system
is functioning normally.

The oxygen sensor output voltage and the short±term fuel trim value can be read using the OBD II scan
tool or TOYOTA hand±held tester.
DI6V7±02

DI±62
± DIAGNOSTICSENGINE
2001 PRIUS (RM778U)
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 Check air induction system (See page SF±1).
NG Repair or replace.
OK
2 Check injector injection (See page SF±12).
NG Replace injector.
OK
3 Check mass air flow meter and engine coolant temp. sensor
(See page SF±22 and SF±49).
NG Repair or replace.
OK
4 Check for spark and ignition (See page IG±1).
NG Repair or replace.
OK

± DIAGNOSTICSENGINE
DI±65
2001 PRIUS (RM778U)
DTC P0300 Random/Multiple Cylinder Misfire Detected
DTC P0301 Cylinder 1 Misfire Detected
DTC P0302 Cylinder 2 Misfire Detected
DTC P0303 Cylinder 3 Misfire Detected
DTC P0304 Cylinder 4 Misfire Detected
CIRCUIT DESCRIPTION
Misfire: The ECM uses the crankshaft position sensor and camshaft position sensor to monitor changes in
the crankshaft rotation for each cylinder.
The ECM counts the number of times the engine speed change rate indicates that misfire has occurred. And
when the misfire rate equals or exceeds the count indicating that the engine condition has deteriorated, the
MIL lights up.
If the misfire rate is high enough and the driving conditions will cause catalyst overheating, the MIL blinks
when misfiring occurs.
DTC No.DTC Detecting ConditionTrouble Area
P0300Mi fi i f d li d i d t t d d i ti l

Open or short in engine wire

Connector connection

Vacuum hose connection

I
gnition systemP0300
P0301
P0302
P0303
P0304
Misfiring of random cylinders is detected during any particular
200 or 1,000 revolutions
For any particular 200 revolutions for the engine, misfiring is
detected which can cause catalyst overheating
(This causes MIL to blink)

Ignition system

Injector

Fuel pressure

Manifold absolute pressure sensor

En
gine coolant temp. sensorP0304(This causes MIL to blink)
Engine coolant tem. sensor

Compression pressure

Valve clearance

Valve timing

ECM
HINT:

When the 2 or more codes for a misfiring cylinder are recorded repeatedly but no random misfire code
is recorded, it indicates that the misfires were detected and recorded at different times.

There is a case where the cylinder other than memorized has an accidental fire (the cylinder which is
one ahead of fired cylinder), so. at the time of checking all the checking items and if there is no ab-
normality, check the cylinder which is different from the recorded cylinder as fired.
DI6V8±03

P03792
± DIAGNOSTICSENGINE
DI±67
2001 PRIUS (RM778U)
(f) Turn ignition switch OFF and wait at least 5 seconds.
INSPECTION PROCEDURE
HINT:

If is the case that DTC besides misfire is memorized simultaneously, first perform the troubleshooting
for them.

Read freeze frame data using TOYOTA hand±held tester or OBD II scan tool. Because freeze frame
data 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.

When the vehicle is brought to the workshop and the misfire is not occurred, misfire can be confirmed
by reproducing the condition or freeze frame data. Also, after finishing the repair, confirm that there
is no misfire. (See the confirmation driving pattern)

When either of SHORT FT #1, LONG FT #1, SHORT FT #2 or LONG FT #2 in the freeze frame data
is besides the range of ±20%, there is a possibility that the air±fuel ratio is inclining either to ºrichº
(±20% or less) or ºleanº (+20% or more).

When COOLANT TEMP in the freeze frame data is less than 80°C (176°F), there is a possibility or
misfire only during warming up.

In the case that misfire cannot be reproduced, the reason may be because of the driving with lack or
fuel, the use of improper fuel, a stain of ignition plug, and etc.
1 Check wire harness, connector and vacuum hose in engine room.
CHECK:
(a) Check the connection conditions of wire harness and connector.
(b) Check the disconnection, piping and break of vacuum hose.
NG Repair or replace, then confirm that there is no
misfire. (See the confirmation driving pattern)
OK
2 Check spark plug and spark of misfiring cylinder.
PREPARATION:
Remove the spark plug (See page IG±1).
CHECK:
(a) Check for carbon deposits on electrode.
(b) Check electrode gap.
OK:
(a) No large carbon deposit present.
Not wet with gasoline or oil.
(b) Electrode gap: 1.0 ± 1.2 mm (0.039 ± 0.047 in.)
PREPARATION:
(a) Install the spark plug to ignition coil and connect the igni-
tion coil connector to ignition coil.

± DIAGNOSTICSENGINE
DI±69
2001 PRIUS (RM778U)
OK Go to step 5.
NG
4 Check resistance of injector of misfiring cylinder (See page SF±9).
NG Replace injector.
OK
Check for open and short in harness and
connector between injector and ECM
(See page IN±41).
5 Check fuel pressure (See page SF±6).
NG Check and repair fuel pump and fuel pipe line
(See page SF±1).
OK
6 Check injector injection (See page SF±12).
NG Replace injector.
OK
7 Check mass air flow merer and engine coolant temp. sensor
(See page SF±22 and SF±49).
NG Repair or replace.

DI±154
± DIAGNOSTICSENGINE
2001 PRIUS (RM778U)
2 Check remaining amount of fuel.
NG Supply fuel.
OK
3 Check air induction system (See page SF±1).
NG Repair or replace.
OK
4 Check for umusual noise or vibration when starting engine or racing.
NG Repair or replace.
OK
5 Check fuel pressure (See page SF±6).
NG Check and repair fuel pump and fuel pipe line
(See page SF±19).
OK
6 Check air flow meter (See page SF±22) and engine coolant temp. sensor
(See page SF±49).
NG Repair or replace.
OK

Engine ECU
TROUBLE CODE
CALC LOAD
ENGINE SPD
COOLANT TEMP
INTAKE AIR
VEHICLE SPD
SHORT FT #1
LOND FT #1
FUEL SYS #1
FUEL SYS #2
ENG RUN TIME
BATTERY
INJECTOR
INJ VOL FB
FEL FB COEF
A/F LEARN
PURGE LEARN
KCS FEEDBACK
REQ ENQ TORQ
RAM MONITOR
ENG RUN SIG
ACC RACING SIG
ENG WARM UP SIG
ENG RUN PERM
FC STATUS
ENG STP LIMIT%
rpm
%
%
V
ms
%
%
degree
KW
ON / OFF
ON / OFF
ON / OFF
EMPS ECU
TROUBLE CODE
TRQ1
TRQ2
WRR
WRL
MOTOR ACTUAL
COMMAND VALUE
STR ANGL VEL
THERMISTOR TEMP
PIG SUPPLY
IG SUPPLY
TRQ1 ZERO VAL
TRQ2 ZERO VALV
V
V V V A
A
deg/s
ON / OFF°F ( °C)
°F ( °C)
mph ( km/h)
mph ( km/h)
mph ( km/h)
°F ( °C) DI±186
± DIAGNOSTICSHYBRID VEHICLE CONTROL SYSTEM
2001 PRIUS (RM778U)