power steering TOYOTA PRIUS 2001 Service Workshop Manual

F12828
ON
RLY
PGND
F11788
5
13
2
Open
Continuity
5
2 1
3
5
2 1
3 Continuity
± DIAGNOSTICSELECTRIC MOTOR POWER STEERING
DI±489
2001 PRIUS (RM778U)
INSPECTION PROCEDURE
1 Check voltage between terminals RLY and PGND of EMPS ECU connector.
PREPARATION:
Remove the EMPS ECU with connectors still connected.
CHECK:
Turn the ignition switch ON and measure the voltage between
terminals RLY and PGND of EMPS ECU connector.
OK:
Voltage: 9 ± 14 V
OK Check or replace EMPS ECU.
NG
2 Check EMPS relay.
PREPARATION:
Remove the EMPS relay from the engine room R/B No. 3.
CHECK:
Check the continuity between each terminal of the EMPS relay.
OK:
Terminals 1 and 2Continuity (Reference value 80 W)
Terminals 3 and 5Open
CHECK:
(a) Apply battery positive voltage between terminals 1 and 2.
(b) Check the continuity between the terminals.
OK:
Terminals 3 and 5Continuity

F12863
Instrument
Panel J/BECU±B
Fuse
DI±490
± DIAGNOSTICSELECTRIC MOTOR POWER STEERING
2001 PRIUS (RM778U)
NG Replace EMPS relay.
OK
3 Check ECU±B fuse.
PREPARATION:
Remove the ECU±B fuse from instrument panel J/B.
CHECK:
Check the continuity of ECU±B fuse.
OK:
Continuity
NG Check for short in harness and all components
connected to ECU±B fuse (See attached wiring
diagram).
OK
Check for open and short circuit in harness and connector between EMPS ECU and battery
(See page IN±41).

F12840
EMPS ECU
WL
E67
Y 3
IP1 L 11 Multiinformation Display
22
L
Instrument Panel J/B
IG1 Relay
3
51
2H GAUGE
2A5
W
FL Block No. 1
1
F11 F131
B±G
1 MAIN FL Block No. 2 F18
BatteryDC/DC
± DIAGNOSTICSELECTRIC MOTOR POWER STEERING
DI±491
2001 PRIUS (RM778U)
DTC C1556/56 P/S Warning Light Circuit
CIRCUIT DESCRIPTION
DTC No.DTC Detecting ConditionTrouble Area
C1556/56There is a malfunction in PS warning light circuit.
Multiinformation display

EMPS ECU
WIRING DIAGRAM
DI7RB±01

F12829
ON
WL
DI±492
± DIAGNOSTICSELECTRIC MOTOR POWER STEERING
2001 PRIUS (RM778U)
INSPECTION PROCEDURE
1 Check voltage between terminals WL of EMPS ECU connector and body ground.
PREPARATION:
Remove the EMPS ECU with connectors still connected.
CHECK:
Turn the ignition switch ON and measure the voltage between
terminals WL of EMPS ECU connector and body ground.
OK:
Voltage: 9 ± 14 V
NG Check and replace EMPS ECU.
OK
2 Check for open and short circuit in harness and connector between EMPS ECU
and multiinformation display (See page IN±41).
NG Repair or replace harness or connector.
OK
Check multiinformation display circuit
(See page BE±97).

DI±494
± DIAGNOSTICSELECTRIC MOTOR POWER STEERING
2001 PRIUS (RM778U)
DTCAlways ONMalfunction in EMPS ECU
CIRCUIT DESCRIPTION
DTC No.DTC Detecting ConditionTrouble Area
Always ONThere is a malfunction in the EMPS ECU internal circuit.

Power source circuit

EMPS ECU

PS warning light circuit
INSPECTION PROCEDURE
1 Is DTC output?
Check DTC on page DI±460.
YES Repair circuit indicated by output code.
NO
2 Is normal code displayed?
YES Check and replace EMPS ECU.
NO
3 Does PS warning light goes off?
YES Check for open or short circuit in harness and
connector between ECU±IG fuse and EMPS
ECU (See page IN±41).
NO
DI7RD±01

± DIAGNOSTICSELECTRIC MOTOR POWER STEERING
DI±495
2001 PRIUS (RM778U)
4 Check battery positive voltage.
PREPARATION:
Start the engine.
CHECK:
Check the battery positive voltage.
OK:
Voltage: 9 ± 14 V
NG Check and repair charging system.
OK
5 Check operation of PS warning light.
PREPARATION:
(a) Turn the ignition switch OFF.
(b) Disconnect the connector from the EMPS ECU.
(c) Turn the ignition switch ON.
CHECK:
Check the PS warning light goes OFF.
OK Check and replace EMPS ECU.
NG
Check for short circuit in harness and connector between multiinformation display and EMPS
ECU, multiinformation display and DLC3 (See page IN±41).

F12842
EMPS ECU
Tc
E63
P±B
C CJ16
J/C
P±B 2
ID1 P±B
E EJ26
J/C
P±B 13
Tc
5
SGBR14
ID2BR
BR 14
IO1
EB DLC3 DI±496
± DIAGNOSTICSELECTRIC MOTOR POWER STEERING
2001 PRIUS (RM778U)
Tc Terminal Circuit
CIRCUIT DESCRIPTION
Connecting terminals Tc and CG of the DLC3 causes the EMPS ECU to display the DTC by flashing the PS
warning light.
WIRING DIAGRAM
DI7RE±01

F09678
ON
Tc
CG
± DIAGNOSTICSELECTRIC MOTOR POWER STEERING
DI±497
2001 PRIUS (RM778U)
INSPECTION PROCEDURE
1 Check voltage between terminals Tc and CG of DLC3.
CHECK:
Turn the ignition switch ON and measure the voltage between
terminals Tc and CG of the DLC3.
OK:
Voltage: 9 ± 14 V
OK If PS warning light does not blink even after Tc
and CG are connected, EMPS ECU may be de-
fective.
NG
2 Turn the ignition switch OFF, and check for open and short circuit in harness
and connector between EMPS ECU and DLC3, and DLC3 and body ground (See
page IN±41).
NG Repair or replace harness or connector.
OK
Check and replace EMPS ECU.

F12844
EMPS ECU
Ts
E69
B BJ16
J/C
3
ID1 GR±G
14
Ts
5
SGBR14
ID2BR
BR 14
IO1
EB DLC3
GR±G GR±G DI±498
± DIAGNOSTICSELECTRIC MOTOR POWER STEERING
2001 PRIUS (RM778U)
Ts Terminal Circuit
CIRCUIT DESCRIPTION
The sensor check circuit detects abnormalities in the speed sensor signal which cannot be detected by the
DTC check.
Connecting terminals Ts and CG of the DLC3 starts the check.
WIRING DIAGRAM
DI7RF±01

F09679
ON
Ts
CG
± DIAGNOSTICSELECTRIC MOTOR POWER STEERING
DI±499
2001 PRIUS (RM778U)
INSPECTION PROCEDURE
1 Check voltage between terminals Ts and CG of DLC3.
CHECK:
Turn the ignition switch ON and measure the voltage between
terminals Ts and CG of the DLC3.
OK:
Voltage: 9 ± 14 V
OK If PS warning light repeats turning ON and OFF
even after Ts and CG are connected, EMPS ECU
may be defective.
NG
2 Turn the ignition switch OFF, and check for open and short circuit in harness
and connector between EMPS ECU and DLC3, DLC3 and body ground (See page
IN±41).
NG Repair or replace harness or connector.
OK
Check and replace EMPS ECU.