1991 ACURA NSX Service Repair Manual

Description

Lock-up System (cont'd)

No Lock-up

Pressurized fluid regulated by the modulator works on both ends of the lock-up shift valve and on the left side of the lock-

up control valve. Under this condition, the pressure on both ends of the lock-up shift valve are equal, and the shift valve is

moved to the right side by the tension of the valve spring alone. The fluid from the oil pump will flow through the left side

of the lock-up clutch to the torque converter; i.e., the lock up clutch is in OFF condition.

NOTE: When used,
"left"
or
"right"
indicates direction
on the
flowchart.

THROTTLE B PRESSUREProCarManuals.com

Partial Lock-up

Lock-up Control Solenoid Valve A: ON Lock-up Control Solenoid Valve B: OFF

The TCM switches the solenoid valve A to ON to release the modulator pressure in the left cavity of the lock-up shift

valve. The modulator pressure in the right cavity of the lock-up shift valve overcomes the spring force, thus the lock-up

shift valve is moved to the left side.

The torque converter pressure is spearated into two passages:

Torque Converter Inner Pressure: entered into right side—to engage lock-up clutch

Torque Converter Back Pressure: entered into left side—to disengage lock-up clutch

The back pressure (F2) is regulated by the lock-up control valve whereas the position of the lock-up timing valve B is

determined by the throttle B pressure, tension of the valve spring and pressure regulated by the modulator. Also the

position of the lock-up control valve is determind by the throttle valve B pressure, back pressure of the lock-up control

valve and torque converter pressure regulated by the check valve. In low speed range, the throttle B pressure working

on the right side of the lock-up control valve is low, causing the valve to be moved to the right side. With the lock-up

control solenoid valve B kept OFF, the modulator pressure is maintained in the left end of the lock-up control valve; in

other words, the lock-up control valve is moved slightly to the left side. This slight movement of the lock-up control

valve causes the back pressure to be lowered slightly, resulting in partial lock-up.

NOTE:
When used,
"left"
or
"right"
indicates direction
on the
flowchart.

THROTTLE B PRESSURE

MODULATOR PRESSURE

(cont'd)ProCarManuals.com

Description

Lock-up System (cont'd)

Half Lock-up

Lock-up Control Solenoid Valve A: ON Lock-up Control Solenoid Valve B: ON

The modulator pressure is released by the solenoid valve B, causing the modulator pressure in the left cavity of the lock-

up control valve to lower.

Also the modulator pressure in the left cavity of the lock-up timing valve B is low. However the throttle B pressure is

still low at this time, consequently the lock-up timing valve B is kept on the right side by the spring force.

With the lock-up control solenoid valve B turned ON, the lock-up control valve is moved somewhat to the right side,

causing the back pressure (F2) to lower. This allows a greater amount of the fluid (F1) to work on the lock-up clutch

so as to engage the clutch. The back pressure (F2) which still exists prevents the clutch from engaging fully.

NOTE:
When used,
"left"
or
"right"
indicates direction
on the
flowchart.

MODULATOR PRESSURE
THROTTLE B PRESSUREProCarManuals.com

Full Lock-up

Lock-up Control Solenoid Valve A: ON Lock-up Control Solenoid Valve B: ON

When the vehicle speed further increases, the throttle B pressure is increased in accordance with the throttle opening.

The lock-up timing valve B overcomes the spring force and moves to the left side. Also this valve closes the oil port

leading to the torque converter check valve.

Under this condition, the throttle B pressure working on the right end of the lock-up control valve becomes greater than

that on the left end (modulator pressure in the left end has already been released by the solenoid valve B); i. e., the lock-

up control valve is moved to the left side. As this happens, the torque converter back pressure is released fully, causing

the lock-up clutch to be engaged fully.

NOTE: When used,
"left"
or
"right"
indicates direction
on the
flowchart.

MODULATOR PRESSURE

(cont'd)
THROTTLE B PRESSUREProCarManuals.com

Description

Lock-up System (cont'd)

Deceleration Lock-up

Lock-up Control Solenoid Valve A: ON Lock-up Control Solenoid Valve B: Duty Operation (ON OFF)

The TCM switches the solenoid valve B to ON and OFF alternately at high speeds under certain conditions.

The slight lock-up and half lock-up regions are maintained so as to lock the torque converter properly.

NOTE:
When used,
"left"
or
"right"
indicates direction
on the
flow chart.

MODULATOR PRESSURE
THROTTLE B PRESSUREProCarManuals.com

ATF Cooler

The radiator is mounted at the front of the vehicle. The ATF cooler is installed directly on the transmission housing. The

ATF is cooled by the engine coolant.

OUTLET HOSE
INLET HOSE

Coolant

ATF COOLERProCarManuals.com

Component Location

LOCK-UP CONTROL

SOLENOID VALVE

ASSEMBLY

MAINSHAFT SPEED SENSOR
FRONT
SHIFT CONTROL

SOLENOID VALVE

ASSEMBLY

ENGINE COOLANT TEMPERATURE (ECT) SENSOR

Engine Compartment

COUNTERSHAFT SPEED SENSOR

TRANSMISSION CONTROL MODULE (TCM)

TCS CONTROL UNIT

ENGINE CONTROL MODULE (ECM)
THROTTLE POSITION (TPI

SENSOR
ACCEL PEDAL

SENSORProCarManuals.com

Troubleshooting Procedures

When the Transmission Control Module (TCM) senses an abnormality in the input or output systems, the indicator
light in the gauge assembly will blink. However, when the Service Check Connector (located to the lower right of the glove compartment) is connected with a jumper wire, the indicator light will blink the Diagnostic Trouble Code (DTC)

when the ignition switch is turned on.

When the indicator light has been reported on, connect the two terminals of the Service Check Connector together.
Then turn on the ignition switch and observe the indicator light.
Codes 1 through 9 are indicated by individual short blinks. Codes 10 through 16 are indicated by a series of long and
short blinks. One long blink equals 10 short blinks. Add the long and short blinks together to determine the code. After
determining the code, refer to the electrical system Symptom-to-Component Chart on page 14-52 and 53. SERVICE CHECK
CONNECTOR
Connect with jumper wire.

INDICATOR
Some PGM-FI problems will also make the indicator light come on After repairing the PGM-FI system, disconnect the
CLOCK fuse (7.5 A) in the main relay box for more than 10 seconds to reset the TCM memory.
long short
See DTC 1

See DTC 2

See DTC 14

LIGHT

short
PGM-FI system
The PGM-FI system on this model is a sequential multiport fuel injection system. Disconnecting the CLOCK fuse also cancels the radio preset stations and the clock setting. Make note of the radio
presets before removing the fuse so you can reset them.

NOTE:ProCarManuals.com