ACURA NSX 1991 Service Repair Manual

Component Location Index
INDICATOR LIGHT
ACTIVATION LIGHT INDICATOR LIGHT
UNDER-HOOD
FUSE/RELAY BOX
ABS
CONTROL UNIT
STEERING

ANGLE SENSOR
(page 19-138)
TCS SWITCH(page 19-137)
UNDER-DASH FUSE BOX

A/T GEAR POSITION
SWITCH
FAIL-SAFE RELAY

(page 19-137)
ENGINE

COMPARTMENT

FUSE/RELAY BOX

TRANSMISSON

CONTROL

MODULE (TCM)
ENGINE
GROUND
TCS CONTROL
UNIT
ENGINE CONTROL
MODULE (ECM)
ACCELERATOR

PEDAL

ANGLE
SENSOR
THROTTLE

ACTUATOR

THROTTLE
POSITION (TP)

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System Description

TCS Control unit

Acceleration Control:

The TCS control unit gets signals from the wheel sensors about the rotational speed of each wheel. Traction control

is activated when the rotational speed of the driving wheels differs from the rotational speed of the driven wheels (i.e.,

vehicle speed).

Handling Control:

Based on signals about driving wheel and driven wheel rotational speeds, the control unit calculates the car's "yaw"

rate (i.e., the turn rate of the car's body). Based on signals from the steering angle sensor, the control unit also calculates

the yaw rate expected by the driver. If the difference between actual and expected yaw rates is substantial—that is,

if the direction of the car's body will exceed the driver's expected line—the control unit signals the throttle actuator,

which closes the throttle valve, thus reducing engine power and maintaining the expected line.

Rough Road Control:

Based on signals from the wheel sensors, the control unit detects a rough road based on frequency of wheel rotational

vibration. The control unit then signals the throttle actuator to relax engine power, thus improving acceleration efficiency.

Grip Control:

Based on signals about wheel speed and yaw rate, the control unit determines the efficiency of the grip of the tires on

the road and signals the throttle actuator to relax engine power if necessary, thus improving grip.
Construction and Function

DRIVE WHEELS

Right wheel

Left wheel
WHEEL SENSORS

Driving Wheel

Speed
Average speed

of left and

right wheels

Vehicle speed

Advance acceleration

Tire grip control

Acceleration

control

Target slip

ratio

Engine control block

ENGINE CONTROL

MODULE (ECM)
Throttle actuator (step motor)
Throttle valve control
Handling control
Rough road

detection

Rough road

control
Reference yaw rate

Lateral

acceleration
TCS CONTROL UNIT
STEERING ANGLE SENSOR

DRIVEN WHEELS

Right wheel
Left wheel

Actual

yaw rate
Rotational

vibration
Speed difference in the

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Fail-Safe Function:

If the control unit detects an abnormality, it shuts the

traction control system off and causes the TCS in-

dicator light to come on. However if the abnormality is

detected while the TCS is activated, the control unit

first establishes the appropriate wheel spin velocity,

then shuts the system down, thus preventing excessive

wheel spin.

Self-Diagnosis Function:

If the control unit detects an abnormality, it records a

Diagnostic Trouble Code (DTC) which can be used to

diagnose the problem. The DTC is shown at the TCS in-

dicator light when the Service Check connector ter-

minals are connected with a jumper wire.

Steering Angle Detection

Steering angle is detected by the steering angle sensor,

located on the steering column. The sensor uses two

magneto-resistor (MR) elements to determine steering

angle and direction of rotation. When the driver turns

the steering wheel, a magnet in the steering shaft

generates waves in the "MR" elements. These waves

are amplified and converted into signals which the con-

trol unit can interpret as angle and direction of turn.

Vehicle Speed Detection

Wheel rotation speed is detected by the wheel sensors,

located at each wheel. The signals are sent to the con-

trol unit, which compares each wheel's speed and de-

termines whether traction control is required.
MR ELEMENT

WHEEL SENSOR
GEAR PULSER
MR

ELEMENT
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System Description

Engine Output Control

When the TCS is activated, the control unit signals the throttle actuator, located next to the throttle valve. The throttle

actuator is linked to the throttle valve through a series of reduction gears. Although the accelerator pedal position is

still within the driver's control, the throttle valve is automatically relaxed to achieve optimum traction.
Construction and Function

LOST MOTION SPRING

(INSIDE RETURN SPRING)

THROTTLE VALVE

RETURN SPRINGS

DURING NORMAL DRIVING:

LOST

MOTION

SPRING

THROTTLE

LEVER

THROTTLE

RETURN SPRING
THROTTLE DRUM

THROTTLE

VALVE

THROTTLE ACTUATOR

(STEP MOTOR)
Movement of parts

while accelalator pedal open.

Movement of parts while

TCS is actuated.
DURING TCS ACTUATION:
THROTTLE ACTUATOR

(STEP MOTOR)
THROTTLE POSITION SENSOR
THROTTLE VALVE
THROTTLE DRUM

ACCELERATOR PEDAL

ANGLE SENSOR

TCS THROTTLE

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Troubleshooting
TCS Indicator Light

Temporary Driving Conditions:
1. The TCS indicator light will come on and the control unit memorizes the Diagnostic Trouble Code (DTC) under cer-
tain temporary conditions:
2. If the TCS indicator light does not come back on after correcting the tire or tire pressure problem, the TCS system is
OK.

NOTE: Remove the ABS 2.3 (20 A) fuse for at least 3 seconds to clear the DTC from the TCS control unit memory.
TCS Diagnostic Trouble Code (DTC) Indication: 1. Stop the engine.
2. Turn the ignition switch on and confirm that the TCS indicator light comes on.
3. Turn the ignition switch off.
4. Connect the two terminals of the Service Check Connector with a jumper wire.
5. Turn the ignition switch on, but do not start the engine.6. Record the blinking frequency of the TCS indicator light. The blinking frequency indicates the DTC. Long blinks in- dicate the main code: short blinks indicate the sub-code.
7. Refer to the Troubleshooting Guide (page 19-84) for repair information. The spare tire is installed, or a tire of the improper size is installed.
The tire pressures are not correct.
SERVICE CHECK CONNECTOR (BLU)
SERVICE CHECK

CONNECTOR (BLU)
INDICATOR LIGHTProCarManuals.com

The TCS control unit has three memory registers. When a problem occurs, the control unit stores the Diagnostic Trou-
ble Code (DTC) in the first memory register. If another problem occurs, or the same problem occurs again, the control
unit moves the first code to the next memory register and stores the second code in the first register. If there's a thirdproblem occurrence, the two existing code are moved up one register and the third code is stored in the first register.
If problems continue to occur, the oldest code is moved out of the last register and lost, and the most recent code is
stored in the first register. The TCS indicator light will not come on again after the engine starts unless another problem occurence is detected.

However, there will still be a code stored in the control unit's memory.

After the repair is completed, disconnect the jumper wire from the Service Check connector and remove the ABS 2.3
fuse (20 A) from the main relay box for at least 3 seconds to erase the control unit's memory. The control unit's memory is erased if the connector is disconnected from the control unit, or if the control unit is
removed from the car.

NOTE:

a: 2.0
sec.
c: 1.2
sec.
e: 0.3
sec.
g: 3.8
sec.

b: 0.5
sec.
d: 1.0
sec.
f: 2.5
sec.

Ignition

switch on

LIGHT

ON

LIGHT

OFF
First inspection Second inspection Third inspection First inspection

DTC 2-1 DTC 2 DTC 4-2 DTC 2-1

Engine start2nd cycle
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Troubleshooting

Troubleshooting GuideProCarManuals.com

There should be continuity between the A and B termi-

nals when the battery is connected to the C and D ter-

minals.

There should be no continuity between the A and B ter-

minals when the battery is disconnected.
Fail-Safe Relay Test
Electronic Components

TCS Switch Test

There should be continuity between the D and E termi-

nals when the switch is pushed and there should be no

continuity when the switch is relesed.

Indicator light

Switch

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2. Disconnec t th e 5- P connecto r fro m th e steerin g an -
gl e sensor .
3 . Remov e th e steerin g angl e senso r mountin g bolts ,
the n remov e th e steerin g angl e sensor .
NOTE : Tak e car e no t t o dro p th e adjustin g shi m
use d betwee n th e steerin g angl e senso r an d senso r
mountin g bracket .
CAUTION : Tak e car e no t t o damag e o r dro p th e
steerin g angl e senso r a s it i s sensitive . 2
. Connec t th e 5- P connecto r t o th e steerin g angl e
sensor .
3. Instal l th e steerin g colum n covers .
4 . Perfor m th e steerin g angl e senso r syste m chec k (Se e
pag e 19-96 ).
I f ther e i s a n abnormalty , chec k th e troubleshoot -
in g flowchar t (se e pag e 19-96 ).
NOTE :
Installation :
1. Instal l th e steerin g angl e senso r b y tightenin g 2 bolt s
an d mak e sur e th e adjustin g shi m i s installe d
properly.
CAUTION : D o no t appl y an y greas e o r oi l t o th e ad -
justin g shim .
Removal :
1. Remov e th e steerin g colum n covers .
Electroni c Compornent s
Steering Angl e Senso r Replacemen t
STEERING
ANGL E
SENSO R
BOLTS
There is n o nee d to selec t (replace ) th e shi m whe n
th e steerin g angl e senso r i s replaced .
Us e th e origina l shim .
Selectio n (Replacement ) o f th e adjustin g shi m (fo r
adjustin g th e ai r gap ) i s require d onl y whe n th e
steerin g colum n assembl y (withou t th e sensor ) i s
replaced .
STEERIN GANGLESENSO R
BOLT
S
1 0 N ·m (1. 0 kg-m , 7. 2 Ib-ft )
ADJUSTIN GSHIM
Detec t
part .
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Selection of the adjusting shim for the steering angle sensor air gap adjustment.

NOTE:

The adjustment of the air gap between the steering shaft and the steering angle sensor should be carried out

in order to obtain adequate sensor output.

The adjusting shim reference number is stamped on the steering column. Adequate air gap can be kept by select-

ing the adjusting shim with the reference number.

Selection of The Adjusting Shim

Reference Number Locations

REFERENCE

NUMBER

STEERING

COLUMN
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