1991 ACURA NSX light

System Description

Electrical Power Steering (EPS)

Outline

The NSX uses an electric motor-driven power steering, which possesses the characteristics best suited for a mid engine

automobile. This system is a power-assisted steering device, with a motor inside the steering gearbox driven by the EPS

control unit and power unit. Its distinctive features are described below:

ALTERNATOR

VEHICLE

SPEED SENSOR
STEERING WHEEL

EPS CONTROL UNIT

POWER UNIT

BATTERY

STEERING GEARBOX
STEERING

COLUMN
Minimized loss of engine horsepower and decreased fuel consumption.

A linear steering feel and the reduction of kickback.

The system is compact and lightweight because it requires no complicated hydraulic piping, etc.ProCarManuals.com

FUSE BOX
System Description

Major Components

The Electrical Power Steering system is composed of the following major components:

EPS CONTROL UNIT

COUNTERSHAFT

SPEED SENSOR

ALTERNATOR
SPEEDOMETER
EPS INDICATOR

LIGHT
STEERING

SENSOR
BATTERY
POWER UNIT

MOTOR

IGNITION

SWITCH
A steering gearbox that converts rotary operation of the steering wheel into transverse operation via a rack and pinion

mechanism. Steering sensors and an actuating motor are incorporated.

A control unit that computes the optimum amount of power assistance, taking into account steering torque, steering

speed, and vehicle speed. Selfdiagnosis functions are included.

A power unit that drives the motor according to the signals from the EPS control unit. A current sensor is built in to

give feedback information to the EPS control unit. Two relays shut off the power if a problem in the system occurs.

A speed sensor, the countershaft speed sensor, send vehicle speed signal to the EPS control unit. Also the

speedometer send vehicle speed signal to the EPS control unit. Two signals are used as a double-check.ProCarManuals.com

Self-Diagnosis Function

The EPS control unit monitors the system inputs and outputs, and the driving current of the motor. If there is a problem

in the system, the control unit turns the system off by actuating the relay in the power unit. Power assist stops and

normal manual steering operation resumes. The control unit also turns the EPS indicator light on to alert the driver, and

memorizes the problem in the form of a code. Connecting the terminals of the service check connector with a jumper

wire enables the EPS indicator light to blink the problem code when the ignition switch is turned on.

Unloader Control

If the steering wheel is turned fully and held in the full-lock position, the steering torque reaches the maximum point,

and an over-current flows to the motor and the power unit. The control unit detects this and reduces the current flow

to the motor.

Average Moving Current Control

The electric current flow to the motor is estimated from the current values detected by the current sensor, and the aver-

age current is obtained at two second intervals. The motor driving current is suppressed when the average current value

exceeds a predetermined marginal value. The control unit regurates the motor current during continuous loading to sup-

press any excessive temperature rise in the power unit and the motor.

Over-Voltage Control

If there is an excessive increase in power source voltage due to a poor battery condition, an alternator voltage regulator

problem, etc., the motor assisting force increases, resulting in excessive control. To prevent this, the control unit signals

to the power unit are corrected to ensure that adequate assisting force is generated.ProCarManuals.com

Wiring Locations

EPS CONTROL UNIT

MAIN RELAY BOX

POWER UNIT

TORQUE SENSOR 6-P CONNECTOR/

STEERING WHEEL SPEED SENSOR

4-P CONNECTOR
STEERING GEARBOX

(TORQUE SENSOR/STEERING WHEEL

SPEED SENSOR)
UNDER-DASH FUSE/RELAY BOX
TRANSMISSION CONTROL MODULE (TCM)

22-P CONNECTOR
VEHICLE SPEED SENSOR

(VSS)
ALTERNATOR 4-P CONNECTOR
EPS INDICATOR LIGHTProCarManuals.com

Troubleshooting Procedures

Under normal conditions, the EPS indicator light in the gauge assembly comes on when the ignition switch is turned

to the ON position, then goes off after the engine is started. This indicates that the bulb and its circuits are operating

correctly.

EPS INDICATOR LIGHT

When the EPS control unit senses an abnormality in the system, the control unit memorizes the problem, the EPS indica-

tor light blinks at equal intervals, and the power steering assist is turned off.

When the EPS indicator light has been reported on, connect the two terminals of the service check connector with a

jumper wire. Then turn on the ignition switch and observe the blinking frequency.

SERVICE CHECK

CONNECTOR (BLU)

GRN/WHT

SERVICE CHECK CONNECTOR (BLU)
BLUProCarManuals.com

Troubleshooting

Diagnostic Trouble Code (DTC) Display

When the service check connector terminals are connected with a jumper wire, the EPS control unit blinks the EPS indi-
cator light to indicate the DTC. The DTC is indicated by a series of long and short blinks. One long blink equals 10 shortblinks. Add the long and short blinks together to determine the DTC, then refer to the Troubleshooting Chart on page 17-51.

Example 1.3 seconds
0.28 seconds
1.3 seconds

0.36 seconds
The control unit can memorize any number of simultaneous problems. The DTC is repeated sequentially beginning with
the lowest number.
The DTC is stored in the control unit memory even when the ignition switch is turned off. After repairing the EPS system,
disconnect the CLOCK fuse in the relay box for more than 10 seconds to reset the EPS control unit memory.ProCarManuals.com

Test Harness Installation
Test Harness A

EPS CONTROL UNIT
TEST HARNESS A

07MAZ-SL00100

Test Harness B

TEST HARNESS B

07MAZ-SL00200

STEERING GEARBOX
Test Harness C

POWER UNIT
TEST HARNESS C
07MAZ-SL00300

Power Unit Checker

Connect to the

cigarette lighter
POWER UNIT CHECKER

07MAZ-SL00400

POWER UNIT
OUTPUT
(VIS)

Remove the glove box and disconnect the EPS con-

trol unit connector.

Connect test harness A.
Disconnect the torque sensor and steering speed sen-
sor connectors and connect test harness B. Pull the floor carpet back from the passenger's side
and remove the bass speaker and power unit cover.
Disconnect the connector and connect test harness C.
Pull the floor carpet back from the passenger's side
and remove the bass speaker and power unit cover. Disconnect the connector and connect the power unit
checker.
Remove the cigarette lighter and connect the power

unit checker.ProCarManuals.com

Power SteeringGearbox Removal/Installation (cont'd)

NOTE: Before removing the gearbox, place a stand
jack under the gearbox and front crossbeam to lightly

support them. Lower the gearbox together with the

front crossbeam.
18. Remove the flange bolts and nuts of the gearbox and front crossbeam.
FLANGE NUTS
60 N.m (6.0 kg-m, 43 Ib-ft)
10 x 97 mm

FLANGE BOLT (Crossbeam bracket
to Front crossbeam)

10 x 97 mm

FLANGE BOLT (Crossbeam bracket
to Front crossbeam)
FLANGE NUT

60N .
m

(6.0 kg-m,
43 Ib-ft)
10 x 97 mm

FLANGE BOLT
(Crossbeam bracket
to Front crossbeam)

LEFT SIDE:

RIGHT SIDE:
10 x 84 mm

FLANGE BOLT

60N .
m

(6.0 kg-m, 43 Ib-ft) (Gearbox to Front
crossbeam)
Corrosion resistant bolt/nut
10 x 68 mm

FLANGE BOLT

60N ·
m

(6.0 kg-m, 43 Ib-ft)
(Front crossbeam
to crossbeam bracket)
10 x 68 mm

FLANGE BOLT

60N ·
m

(6.0 kg-m, 43 Ib-ft)
(Front crossbeam to
crossbeam bracket)
10 x 97 mm

FLANGE BOLT

60N·m

(6.0 kg-m, 43 Ib-ft) (Gearbox to Front
crossbeam) 19. Lower the gearbox and front crossbeam with care

so as not to interfere with the radiator pipe.

NOTE: The crossbeam is attached to the cross-
beam bracket with knock pins. Remove the cross-
beam by lightly taping on it with a plastic hammer,

then remove the gearbox.
LEFT CROSSBEAM BRACKET
FRONT CROSSBEAM
GEARBOX

ASSEMBLY

20. When installing the crossbeam to the crossbeam bracket, be sure to align the holes in the crossbeam

with the knock pins on the crossbeam bracket.

CROSSBEAM

BRACKET

KNOCK PIN
FRONT CROSSBEAM RIGHT CROSSBEAM

BRACKET

STEERING

GEARBOX
BRACKET

CUSHION B
MOUNT BASE
FLANGE NUT

60N
·
m

(6.0 kg-m, 43 Ib-ft)ProCarManuals.com