1991 LEXUS SC400 power steering

167
4. AUTO RETURN OPERATION
WHEN THE STEERING IS IN ªAUTO AWAYº CONDITION AND THE IGNITION KEY IS INSERTED INTO THE IGNITION KEY CYLINDER
(UNLOCK WARNING SW ON), A SIGNAL IS INPUT TO TERMINAL UWSW OF TILT AND POWER TELESCOPIC ECU.
AS A RESULT, THE TILT AND POWER TELESCOPIC ECU OPERATES AND THE CURRENT TO TERMINAL +B OF TILT AND POWER
TELESCOPIC ECU FLOWS FROM TERMINAL TEM± OF TILT AND POWER TELESCOPIC ECU "TERMINAL 4 OF COMB. SW "
TERMINAL 1 OF TELESCOPIC CONTROL MOTOR "TERMINAL 2 " TERMINAL 1 OF COMB. SW " TERMINAL TEM+ OF TILT AND
POWER TELESCOPIC ECU " TERMINAL GND2 "GROUND , AND AT THE SAME TIME, CURRENT FLOWS FROM TERMINAL TIM± OF
TILT AND POWER TELESCOPIC ECU "TERMINAL 10 OF COMB. SW "TERMINAL 1 OF TILT CONTROL MOTOR "TERMINAL 2 "
TERMINAL 1 OF COMB. SW "TERMINAL TIM+ OF TILT AND POWER TELESCOPIC ECU "TERMINAL GND2 "GROUND , CAUSING
BOTH THE TILT CONTROL MOTOR AND TELESCOPIC CONTROL MOTOR TO ROTATE. THE MOTORS CONTINUE TO ROTATE UNTIL
THE SIGNALS INPUT FROM THE TILT POSITION SENSOR TO TERMINAL TIS OF TILT AND POWER TELESCOPIC ECU AND FROM THE
TELESCOPIC POSITION SENSOR TERMINAL TES OF TILT AND POWER TELESCOPIC ECU (SIGNALS INFORMING THE ECU OF THE
CURRENT POSITION OF THE STEERING) MATCH THE POSITION MEMORIZED BY THE ECU PRIOR TO AUTO AWAY OPERATION.
IN THIS WAY, THE STEERING POSITION IS AUTOMATICALLY RETURNED TO THE ORIGINAL POSITION.
WHEN THE IGNITION SW IS TURNED FROM OFF TO ON OR THE SHIFT LEVER IS SHIFTED TO A POSITION OTHER THAN P OR N,
AUTO OPERATION IS STOPPED.
C15 TILT AND POWER TELESCOPIC UNIT [COMB. SW]
4±6 : APPROX. 160
WITH TELESCOPIC LONG OPERATION
: APPROX. 360
WITH TILT UP OPERATION
: APPROX. 790
WITH TELESCOPIC SHORT OPERATION
: APPROX. 2.0K
WITH TILT DOWN OPERATION
8±7 : CONTINUITY WITH AUTO SW OFF
8±4 : APPROX. 5K

T 7 (D) TELESCOPIC POSITION SENSOR
6±3 : APPROX. 5K

D10 DOOR LOCK MOTOR, DOOR UNLOCK DETECTION SW AND DOOR OPEN DETECTION SW LH
3±6GROUND :CLOSED WITH FRONT DOOR LH OPEN
D12 DRIVING POSITION MEMORY AND RETURN SW
2±3 : CLOSED WITH DRIVING POSITION MEMORY SW (NO. 1) ON
1±3 : CLOSED WITH DRIVING POSITION MEMORY SW (NO. 2) ON
4±3 : CLOSED WITH DRIVING POSITION MEMORY SW (SET) ON
I15 UNLOCK WARNING SW [IGNITION SW]
9±10: CLOSED WITH IGNITION KEY IN CYLINDER
N 1 A/T INDICATOR SW [NEUTRAL START SW]
9±1 : CLOSED WITH SHIFT LEVER AT P POSITION
T10, T11 TILT AND POWER TELESCOPIC ECU
(A) 4±GROUND : ALWAYS APPROX. 12 VOLTS
(A) 1±GROUND : APPROX. 12 VOLTS WITH IGNITION SW AT ON POSITION
(B) 18±GROUND : ALWAYS APPROX. 12 VOLTS
(A) 6±GROUND : APPROX. 12 VOLTS WITH IGNITION SW ON AND SHIFT LEVER AT ªPº RANGE
(B) 10±GROUND : CONTINUITY WITH IGNITION KEY IN CYLINDER
(A) 7±GROUND : ALWAYS CONTINUITY
(B) 8±GROUND : ALWAYS CONTINUITY
(B) 2±GROUND : CONTINUITY WITH FRONT DOOR LH OPEN
(B) 3±GROUND : CONTINUITY WITH DRIVING POSITION MEMORY SW (NO. 1) ON
(B) 12±GROUND : CONTINUITY WITH DRIVING POSITION MEMORY SW (NO. 2) ON
(B) 11±GROUND : CONTINUITY WITH DRIVING POSITION MEMORY SW (SET) ON
(A) 10±GROUND : APPROX. 12 VOLTS WITH TILT UP OPERATION
(A) 3±GROUND : APPROX. 12 VOLTS WITH TILT DOWN OPERATION
(A) 2±GROUND : APPROX. 12 VOLTS WITH TELESCOPIC SHORT OPERATION
(A) 11±GROUND : APPROX. 12 VOLTS WITH TELESCOPIC LONG OPERATION
: PARTS LOCATION
CODESEE PAGECODESEE PAGECODESEE PAGE
C1728N 127T 732
D1030P 329T10B29
D1230P1127T11A29
I1529R 732
SERVICE HINTS
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177
SRS AIRBAG
NOTICE: When inspecting or repairing the SRS AIRBAG, perform the operation in accord\
ance with the
following precautionary instructions and the procedure and precautions in the Repair Manual for the applicable
model year.

Malfunction symptoms of the airbag system are difficult to confirm, so the diagnostic codes become the most
important source of information when troubleshooting.
When troubleshooting the airbag system, always inspect the diagnostic codes before disconnecting the
battery.

Work must be started after 30 seconds or longer from the time the Ignition SW is set to the ªLOCKº position
and the negative (±) terminal cable is disconnected from the battery.
(The airbag system is equipped with a back±up power source so that if work is started within 30 seconds of
disconnecting the negative (±) terminal cable of the battery, the airbag may be deployed.)
When the negative (±) terminal cable is disconnected from the battery, memory of the clock and audio systems
will be cancelled. So before starting work, make a record of the contents memorized by each me\
mory system.
Then when work is finished, reset the clock and audio system as before.
When the vehicle has tilt and telescopic steering, power seat, outside r\
ear view mirror and power shoulder
belt anchorage, which are all equipped with memory function, it is not possible to make a record of the memory
contents. So when the operation is finished, it will be necessary to explain this\
fact to the customer, and
request the customer to adjust the features and reset the memory.
To avoid erasing the memory of each memory system, never use a back±up \
power supply from outside the
vehicle.

When removing the steering wheel pad or handling a new steering wheel pad, keep the pad upper surfa\
ce
facing upward. Also, lock the lock lever of the twin lock type connector\
at the rear of the pad and take care
not to damage the connector.
(Storing the pad with its metallic surface up may lead to a serious accident if \
the airbag inflates for some
reason).

Store the steering wheel pad where the ambient temperature remains below\
93 °C (200 °F), without high
humidity and away from electrical noise.

Never use airbag parts from another vehicle. When replacing airbag parts\
, replace them with new parts.

Never disassemble or repair the steering wheel pad, center airbag sensor asse\
mbly or front airbag sensors.

Before repairing the body, remove the airbag sensors if during repair shocks are likely to be app\
lied to the
sensors due to vibration of the body or direct tapping with tools or oth\
er parts.

Do not reuse a steering wheel pad or front airbag sensors.
After evaluating whether the center airbag sensor assembly is damaged or not, decide whether or not to reuse
it. (See the Repair Manual for the method for evaluating the center airbag\
sensor assembly.)

When troubleshooting the airbag system, use a high±impedance (Min. 1\
0k W/V) tester.

The vehicle wiring harness exclusively for the airbag system is distinguish\
ed by corrugated yellow tubing, as
are the connectors.

Do not measure the resistance of the airbag squib.
(It is possible this will deploy the airbag and is very dangerous.)

If the wire harness used in the airbag system is damaged, replace the wh\
ole wire harness assembly.
When the connector to the airbag front sensors can be repaired alone (when \
there is no damage to the wire
harness), use the repair wire specially designed for the purpose.
(Refer to the Repair Manual for the applicable Model year for details o\
f the replacement method.)

INFORMATION LABELS (NOTICES) are attached to the periphery of the airbag componen\
ts. Follow the
instructions on the notices.
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