2001 TOYOTA PRIUS light

± 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

± 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

A14462
OX Signal Waveform (Oscilloscope)
500 msec./DivisionOX1
OX2 1.0 V
0.5 V
0 V
1.0 V
0.5 V
0 V
± DIAGNOSTICSENGINE
DI±79
2001 PRIUS (RM778U)
(c) Drive the vehicle at 89 km/h (55 mph) or more for 5 min. or more.
(d) After confirming that the waveforms of the oxygen sensor, bank 1 sensor 1 (OX1), oscillate around 0.5
V during feedback to the ECM, check the waveform of the oxygen sensor, bank 1 sensor 2 (OX2).
HINT:

If there is a malfunction in the system, the waveform of the
oxygen sensor, bank 1 sensor 2 (OX2),is shown on the
left.

There are some cases where, even though a malfunction
exists, the MIL may either light up or not light up.

Normal waveform of OX2 is a smooth line of 0.6 to 0.7 V.
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 P0420) being output?
YES Go to relevant DTC chart.
NO
2 Check gas leakage on exhaust system.
NG Repair or replace.
OK
3 Check for open and short in harness and connector between heated oxygen
sensor (bank 1 sensor 1, 2) and ECM.
NG Repair or replace harness or connector.
OK

A14059
B±G
EFICIR OPN
Relay
MREL Engine Room J/B
1A
B
AECM
FC
F16
Fuel
Pump
IE 5
FL Block No. 1
MAIN
F12
BatteryE8
E9 259
W±B
J17
J/C J1
J/C
IG J7
J/C IA1
IA2
W±B
AA A W±B G±R B±R
F18
FL Block No. 2EFI
Relay
1K 1F
1B10
1F
2 121
3
2
1
3
3
1
11 52 1
3
F13G±R
B±R
7 14
4
G±R
± DIAGNOSTICSENGINE
DI±161
2001 PRIUS (RM778U)
Fuel Pump Control Circuit
CIRCUIT DESCRIPTION
When starting the engine with ignition switch:
HV ECU receives ST signal and decides to start the engine, and send the signal of the engine start prior
signal to the engine ECU by the communicatio between the engine ECU and HV ECU.
Engien ECU receives that signal and turns ON the circuit opening relay slightly earlier, then turns the fuel
pump.
When starting the engine in an intermittent operation:
With the cranking by MG1, NE signal comes in immediately, so the engine ECU receives the generation of
NE signal and turns the fuel pump. (At this time, no refernce of the communication from HV ECU)
When stopping the fuel pump:
When the signal to stop the engine comes in to the engine ECU from HV ECU from HV ECU side, the fuel
pump stops.
At the time of the fuel cut opetation such as deceleration by the engine brake, the fuel pump stops.
WIRING DIAGRAM
DI7T7±01

A14037
Combination MeterECM
Instrument Panel J/B
W
BatteryE10 IG1 Relay
6
J11
J/C IG1C11
C10
ID DC/DCG±R
2A
A 5
W
W±B
F114
3GAUGE
Ignition SW 22
2 3B±Y
21
2 1
1 1
MAINL
AM1
B±G4
FL Block No. 1FL Block No. 2 F1312D
2B 2K 2H
86 5
AM1
W±G
MIL
DI±166
± DIAGNOSTICSENGINE
2001 PRIUS (RM778U)
MIL Circuit Malfunction
CIRCUIT DESCRIPTION
If the ECM detects trouble, the MIL lights up. At this time, the ECM records a DTC in memory.
HINT:
When the ignition switch is ON and ºREADYº indicator light is OFF, the bulb check of the ºMILº is performed
(ºMILº is ON).
When ºMILº is ON, but the DTC of the engine is not memorized, it may be because of HV control system
abnormality, so check HV control system beforehand.
WIRING DIAGRAM
INSPECTION PROCEDURE
HINT:
Troubleshoot in accordance with the chart below for each trouble symptom.
MIL does not light up
Start inspection from step 1 in case of using TOYOTA hand±held
tester and start from step 2 in case of not using TOYOTA hand±
held tester
MIL remains on
After inspection of step 3, start inspection from step 4 in case of
using TOYOTA hand±held tester and start from step 5 in case of
not using TOYOTA hand±held tester
DI6MN±03

DI82J±02
Prius Problem Check Sheet
Vehicle
Specifications
Please fill in the blanks within bold frame.Name of DealerPerson in Charge at
HeadquartersPerson in Charge
at Dealer
Model CodeOffice
Vehicle Delivery Date
Frame No.
Unit No. etc.
Option . . . :
( ) Navigation (equipped by ( ) MOP ( ) dealer) ( ) Cold climate specification
( ) others( )Problem Occurrence Date
Service Entry Date NHW11±
. .
. .Registration datemiles
. .
Contents of complaint (Status when and before/after occurring in
the order of events as correct as possible)Characteristics of Customer
Gender
Age
Occupation
Vehicle used before
Main use area
Frequency in use
Others times/day or
week or month
Status of engineOthers
Interview Results
( ) Male ( ) Female
suburbs ( ) %
Others ( ) ( ) %
city area ( ) %
mountain area ( ) %
Driving ConditionRoad Condition
Vehicle Condition
Vehicle Speed
km/h
( ) when starting
( ) when according
( ) When
normal driving
( ) when
decelerating
( ) when braking
( ) when shopping
( ) when parking
( ) when turning
( ) when
ABS actuating
( ) others
( )( ) flat road
( ) up hill ( ) down
hill incline of
° /%
distance
km
( ) dry paved road
( ) wet paved road
( ) rough paved road
( ) unpaved road
( ) snowy/frozen
road
( ) bump/curb
( ) others
( )( ) when starting
( ) right after
starting
( ) until min.
after starting
( ) until min.
after starting
of driving
( ) when shopping
system
( ) while shopping
engine
( ) when starting
engine
( ) when revolving
engineHV Battery
indication
( ) 4/4 ( ) 3/4
( ) 2/4 ( ) 1/4
( ) unidentified
Shift position
(indication)
( ) P ( ) R ( ) N
( ) D ( ) B
( ) when operating
"Weather:
A/C status
( ) no indication
( ) unidentified
( ) A/C ( ) FULL
( ) OFF
( ) unidentifiedWarning light
(MIL)
( ) ON ( ) OFF
( ) PS
( ) main battery
( ) HV!
( ) engine
( ) charge
( ) output
control
( ) brake
( ) ABS
( ) others
( )
Temperature:
°C
Brake operation
( ) brake slowly
( ) Brake suddenly
( ) use two pedals
system
Frequency in
occurrence
( ) always
( ) sometimes
( ) only once
Fuel level
( ) segmentsmphOdometer Reading
mph
°F km
± DIAGNOSTICSHYBRID VEHICLE CONTROL SYSTEM
DI±175
2001 PRIUS (RM778U)
CUSTOMER PROBLEM ANALYSIS CHECK

Verification Results of Warning Light
Engine
HV
INF. code
HV battery
Vehicle Verification Results
( ) ON ( ) OFF
( ) engine ( ) HV
( ) HV battery
( ) output control warning light
( ) brake ( ) ABS ( ) charge ( ) PS
( ) others
( )Verification Results of Diagnostic Code
Brake
PS
Vehicle Inspection Results (Verification items, reason to identify/presume the cause parts, etc.)
Replacement Parts
problem parts: No/Yes (Sending date: . . )Duplication Status
( ) always
( ) sometimes
( ) no reproduction
Confirmation Results
After Repair
( ) Normal
( ) reproduction
( ) others ( )
DI±176
± DIAGNOSTICSHYBRID VEHICLE CONTROL SYSTEM
2001 PRIUS (RM778U)

B04757
DI82K±02
A14091
F12396
DLC3
TOYOTA Hand±held Tester
± DIAGNOSTICSHYBRID VEHICLE CONTROL SYSTEM
DI±177
2001 PRIUS (RM778U)
PRE±CHECK
1. PRECAUTION
(a) When distinguishing trouble and replace the defective
part, take necessary preventive measures against an
electric shock (See page IN±4).
(b) Some portions of the wiring harness in the THS vehicle
have circuits to which a high voltage is applied. To prevent
an electrical shock, be sure to observe the following:
(1) Wear insulated gloves during inspection.
(2) Remove a service plug and do not start any repair
operation before 5 minutes have passed. Then,
confirm that the voltage at the output terminals has
dropped down to 12 V or less.
(3) Use insulated tools during inspection.
(4) When disengaging the wiring connectors, hold the
connector bodies to avoid pulling the wires. When
engaging the wiring connectors, be sure to engage
them securely.
(c) Do not leave the tools or parts (bolts, nuts, etc.) inside the
cabin.
(d) Do not carry metallic objects such as mechanical pencils
or scales.
2. DIAGNOSIS SYSTEM
(a) Description

The HV control ECU has a self±diagnosis system
by which malfunction in the computer itself or in
THS components is detected and the Hybrid ve-
hicle warning light in the multi±information display
are lighted up.

To check the Diagnostic Trouble Codes (DTC), con-
nect the hand±held tester to the Data Link Connec-
tor 3 (DLC3) on the vehicle. The TOYOTA hand±
held tester also enables you to erase the DTC and
check freeze frame data and various forms of THS
data.