2001 TOYOTA PRIUS warning lights

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W±R
7. 5A
GAUGE
1 2
34
4 8 7
2111134
1 2
3 4
1 2
B18
BL FROM POWER SOURCE SYSTEM (SEE PAGE 66)
R±L
R±L G
W±B W±B
W±B
W±BW±B
W±B
Y±GR
L 4
H17
R 6
DELAY
CIRCUIT S 6
B18
3 4
R 7
BV11
G±W G±R
G±R
G±R
G±R
G±W
G±W
(W/G)
(S/D) (S/D)
C 7
(SHIELDED) BV11I 5
L L
STOP LIGHT
15
7
TO ABS ECU
BO
50
15A
STOP
IBIB
REAR LIGHTS
WARNING LIGHT
[COMB. METER] 3C 3C
IE1 14 STOP LIGHT SW
STOP LIGHT RH
[REAR COMB. LIGHT RH]
STOP LIGHT RH
[REAR COMB. LIGHT LH]
HIGH MOUNTED
STOP LIGHT
[A]
[B]
[I]
[D]
[F]
[H]
[E]
[J]
[M]
[N][K]
[L]
[G]
[C]
LIGHT FAILURE SENSOR
2001 PRIUS (EWD414U)
B HOW TO USE THIS MANUAL
*The system shown here is an EXAMPLE ONLY. It is different to the actual
circuit shown in the SYSTEM CIRCUITS SECTION.

[O]
[P]
[Q]
[R]
[S]
[T]
[U]
[V]
2001 PRIUS (EWD414U)
B HOW TO USE THIS MANUAL
Current is applied at all times through the STOP fuse to TERMINAL 2 of the stop light SW.
When the ignition SW is turned on, current flows from the GAUGE fuse to TERMINAL 8 of the light failure sensor, and also flows
through the rear lights warning light to TERMINAL 4 of the light failure sensor.
STOP LIGHT DISCONNECTION WARNING
When the ignition SW is turned on and the brake pedal is pressed (Stop light SW on), if the stop light circuit is open, the current
flowing from TERMINAL 7 of the light failure sensor to TERMINALS 1, 2 changes, so the light failure sensor detects the
disconnection and the warning circuit of the light failure sensor is activated.
As a result, the current flows from TERMINAL 4 of the light failure sensor to TERMINAL 11 to GROUND and turns the rear lights
warning light on. By pressing the brake pedal, the current flowing to TERMINAL 8 of the light failure sensor keeps the warning
circuit on and holds the warning light on until the ignition SW is turned off.
S6 STOP LIGHT SW
2±1 : Closed with the brake pedal depressed
L4 LIGHT FAILURE SENSOR
1, 2, 7±GROUND : Approx. 12 volts with the stop light SW on
4, 8±GROUND : Approx. 12 volts with the ignition SW at ON position
11±GROUND : Always continuity
: PARTS LOCATION
CodeSee PageCodeSee PageCodeSee Page
C734L436R737
H1736R637S635
: RELAY BLOCKS
CodeSee PageRelay Blocks (Relay Block Location)
118R/B No.1 (Instrument Panel Left)

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: JUNCTION BLOCK AND WIRE HARNESS CONNECTOR
CodeSee PageJunction Block and Wire Harness (Connector Location)
IB20Instrument Panel Wire and Instrument Panel J/B (Lower Finish Panel)
3C22Instrument Panel Wire and J/B No.3 (Instrument Panel Left Side)
: CONNECTOR JOINING WIRE HARNESS AND WIRE HARNESS
CodeSee PageJoining Wire Harness and Wire Harness (Connector Location)
IE142Floor Wire and Instrument Panel Wire (Left Kick Panel)
BV150Luggage Room Wire and Floor Wire (Luggage Compartment Left)
: GROUND POINTS
CodeSee PageGround Points Location
BL50Under the Left Quarter Pillar
BO50Back Panel Center
: SPLICE POINTS
CodeSee PageWire Harness with Splice PointsCodeSee PageWire Harness with Splice Points
I544Cowl WireB1850Luggage Room Wire
SYSTEM OUTLINE
SERVICE HINTS

2001 PRIUS (EWD414U)
WIRELESS DOOR LOCK CONTROL
The current is always sent from DOOR fuse to TERMINAL B of body ECU. At the same time, the current is always sent from
DOME fuse to TERMINAL CPUB of power window master SW, and from ECU±B fuse to wireless door lock receiver. When
ignition SW is turned on, the current is sent from GAUGE fuse to TERMINAL IG of body ECU.
1. WIRELESS DOOR LOCK OR UNLOCK NORMAL OPERATION
*Lock operation
When the LOCK SW of the transmitter is pushed, all the doors are locked.
*Unlock operation
When the UNLOCK SW of the transmitter is pushed, all the doors are unlocked.
2. AUTOMATIC LOCK OPERATION
After all the doors are unlocked by pushing the UNLOCK SW of the transmitter, unless each of the doors is opened or the
ignition key is inserted, all the doors are locked again.
3. VISUAL CONFIRMATION OF LOCK OR UNLOCK FUNCTION
When doors are locked by using the transmitter, the taillight and parking lights blink once. When doors are unlocked by using
the transmitter, the taillights and parking lights blink twice. If UNLOCK SW of the transmitter is pushed while all the doors are
locked, doors are unlocked and the room lights are turned on simultaneously.
4. WIRELESS CONTROL STOP FUNCTION
If the following situations occur, wireless door lock function does not operate.
*When each of the doors opens. (Door courtesy SW is on)
*When ignition key is inserted to ignition SW. (Unlock warning SW is on)
*When ignition SW is on.
5. REPEAT FUNCTION
If the doors are not locked after the lock signal is out put from transmitter by pushing LOCK SW, the lock signal is sent again
to lock the doors.
6. PANIC MODE FUNCTION
When the panic SW of the transmitter is pushed, the horn comes on, and the headlight and taillight flashes.
B8 (A), B9 (B) BODY ECU
15±GROUND : Approx. 12 volts with the ignition SW at ON position
8±GROUND : Always approx. 12 volts
(B) 1±GROUND : Always continuity
W5 WIRELESS DOOR LOCK CONTROL RECEIVER
5±GROUND : Always approx. 12 volts
1±GROUND : Always continuity
U1 UNLOCK WARNING SW
2±1 : Closed with the ignition key in the cylinder
: PARTS LOCATION
CodeSee PageCodeSee PageCodeSee Page
B8A36D1438J23B37
B9B36J1137J24A37
D436J12A37J25B37
D638J13B37J2737
D738J14A37J3338
D838J15B37L438
D938J1637P939
D1038J1737U137
D1138J18A37W537
D1238J19B37
D1338J22A37
SYSTEM OUTLINE
SERVICE HINTS

THS (TOYOTA HYBRID SYSTEM)
182TH22
1. READY Light
2. Output Control
Warning Light 3. Master Warning Light
4. Malfunction Indicator light 5. Discharge Warning Light
6. EMPS Malfunction
Warning Light7. HV Battery Warning Light
8. Hybrid System
Malfunction Warning
Light 32
INDICATOR AND WARNING LIGHT
The warning lights of the Prius are different from those on conventional vehicles. Inspection and repair
should be performed while referring to the troubleshooting section in the 2001 Prius repair manual
(RM778U).

Center Meter 
Multi Information Display 
1. READY lightTurns on when the ignition switch is turned to START to indicate that the ve-
hicle is ready to drive.
2. Output control
warning lightTurns on when the remaining HV battery charge becomes insufficient at R
range or when there is an abnormal temperature rise in the HV battery due
to continuous driving under heavy loads. It may also light when the HV bat-
tery temperature is low (after starting at low temperatures). The hybrid sys-
tem output is limited while this light is on.
Travel at reduced speeds (avoid sudden acceleration) while the light is lit.
3. Master warning
lightTurns on with buzzer sounding by linked operation with warning lights ª6º
to ª8º on the multi center display.
4. Malfunction
indicator lightTurns on when there is a malfunction in the engine control system.
5. Discharge warning
lightTurns on when there is a malfunction in the 12 V charging system (converter
assembly).
If it turns on together with the master warning light and hybrid system
warning light, check the diagnostic code.
6. EMPS malfunction
warning lightTurns on when there is a malfunction in the EMPS control system.
7. HV battery warning
lightTurns on when the HV battery is discharged to the lower limit.
8. Hybrid system
warning lightTurns on when a malfunction in MG1, 2, inverter, HV battery or HV ECU
is detected.

CHASSIS ± BRAKES105
4. Function of Main Components
ComponentsFunction
ABS Warning
LightLights up to alert the driver when the brake ECU detects the
malfunction in the ABS.
Combination
Meter
Brake System

Lights up together with the ABS warning light to alert the driver
when the brake ECU detects the malfunction not only in the ABS
but also in the EBD controlBrake System
Warning Lightbut also in the EBD control.

Lights up to alert the driver when the malfunction occurs in the
brake system.
Stop Light SwitchDetects the brake depressing signal.
Brake Warning BuzzerEmits a continuous sound to inform the driver that the ABS ECU
detects the malfunction in the hydraulic brake booster.
Speed SensorsDetect the wheel speed of each of the four wheels.
Brake ECU

Processes various sensor signals, regenerative brake signals, to
execute control of the ABS control, EBD control, regenerative
coordination control and hydraulic brake booster.

Communicates control data with the HV ECU.
HV ECUMaintains serial communication with the brake ECU to exchange
regenerative coordination control signals.
Hydraulic Brake Booster
Assists with the pedal effort applied to the brake pedal.

Supplies hydraulic pressure.
Brake ActuatorControls the brake fluid pressure to each brake wheel cylinder by
signals from the brake ECU.
Solenoid RelaySupplies power to the ABS's solenoid valve's in the brake actuator.
Pump Motor RelaysControl the pump motor operation in the hydraulic brake booster.

CHASSIS ± STEERING
182CH95
182CH76
Twist Angle
Basic Position
Cornering
Torque
[V]
Voltage
Voltage difference between
outputs 1 and 2 during
straight line driving (0)
Torque Sensor 2
Torque Sensor 1
0 ±+
Right Turn Left Turn127
ii) Steering to the right
When the driver turns the steering to the
right, the steering torque is transmitted to
the pinion shaft's input shaft, causing the
input shaft to rotate. Because the reaction
force of the ground surface acts on the rack
bar, the torsion bar that links the input shaft
and the pinion twists until a torque that
equalizes with the reaction force is gener-
ated. Thus, a relative displacement is
created between the resistor that is secured
onto the input shaft and the contact that is
secured onto the pinion shaft's output shaft.
As a result, the resistance changes, causing
the torque sensor's outputs 1 and 2 to
change as shown in the right diagram. The
EMPS ECU uses this voltage difference to
calculate the power assist torque to drive
the DC motor, thus generating a power as-
sist force in the pinion shaft via the reduc-
tion mechanism.
iii) Steering Hold Condition
The torsion bar shift to a position in which the sum of the driver's steering torque and the motor's assist
torque equalizes with the reaction force of the ground surface in order to maintain the steering holding
condition.
EMPS ECU
1) EMPS Control
The EMPS ECU receives signals from various sensors, judges the current vehicle condition, and deter-
mines the assist ampere to be applied to the DC motor accordingly.
2) Self-Diagnosis
If the EMPS ECU detects a malfunction in the EMPS system, the warning light that corresponds to the
function in which the malfunction has been detected lights up to alert the driver of the malfunction.
The EMPS ECU will also store the codes of the malfunctions. The DTCs (Diagnostic Trouble Codes)
can be accessed through the use of a hand-held tester. For details, see the 2001 Prius Repair Manual (Pub.
No. RM778U).
3) Fail-Safe
If the EMPS ECU detects a malfunction in the EMPS system, the system basically turns OFF the power
to prohibit power assist. As a result, the EMPS system operates the same way as manual steering.
However, depending on the location in which the malfunction occurred, power assist may be provided
by reducing the power assist amperage or by fixing the amount of power assist without relying on the
vehicle speed.

BODY ELECTRICAL ± MULTIPLEX COMMUNICATION SYSTEM 142
SYSTEM OPERATION
1. General
The ECUs that pertain to the body electrical system perform the functions and system controls described be-
low.
Gateway ECU
Conversion of data between AVC-LAN and BEAN
Transmission of vehicle information to the display ECU, in order for it to be displayed on multi-informa-
tion display
Body ECU
Power window system control (Front, Rear passenger only)
Door lock control system control
Wireless door lock remote control system control
Theft deferrent system control
Daytime running light system control
Illuminated entry system control
Light auto turn-off system control
Seat belt warning system control
Key reminder system control
Diagnosis
Meter ECU
Meter control
Illumination and flashing control of indicator and warning lights
Sounding control of warning buzzer
Air Conditioning ECU
Air Conditioning control
ECM
Engine control
Diagnosis
Display ECU
Transmission and reception associated with audio and visual functions

BODY ELECTRICAL ± ACCESSORIES
182BE41
RRP DBody
ECUUARTPower
Window
Master
SwitchDoor Control
Switch (Manual)
Door Control
Switch (Key-linked)
169BE10
Key Unlock
Warning SwitchDoor Courtesy
Switch
Door Lock
MotorsBody
ECU
Serial Data Link
Wireless Door
Control Receiver
Horn
RelayHeadlight
RelayTaillight
RelayTransmitter183
DOOR LOCK CONTROL SYSTEM
The door lock control system has the following features:
This system has a ªkey-linked lock and unlockº, ªkey-confine preventionº and ªmanual unlock prohibi-
tionº functions.
A 2-step unlock function is provided to unlock the driver's door by turning the key cylinder first and to
unlock passenger's door by turning it the second time.
The control of this system is effected by the body ECU. The door lock control signal from the driver's door
is transmitted from the power window master switch to the body ECU through the UART (Universal
Asynchronous Receiver Transmitter).
If you unlock using the ignition key from the conditions in which all the doors are locked, the dome light
will be lighted.

System Diagram 
WIRELESS DOOR LOCK REMOTE CONTROL SYSTEM
The wireless door lock remote control system has the following features:
In this system, the wireless door control receiver performs the code identification process and the body
ECU effects the door lock control. Serial data link is provided for communication between the wireless
door control receiver and the body ECU.
A key-holder type transmitter has been adopted, and it contains the following three switches: the door lock
switch, door unlock switch, and panic switch.
A rolling code system, in which the signal configuration changes each time when a signal is transmitted
by the transmitter, has been adopted.
Panic alarm operation has been adopted.
The verification light function has been adopted. When the transmitter is used to lock or unlock the doors,
this function flashes the taillights to inform that the operation has been completed. However, at the time
of unlocking, the dome light will be lighted.