traction control ACURA NSX 1997 Service Repair Manual

Drive By Wire System

System Description (cont'd)

Cruise Control Function

The ECM controls the throttle valve control motor to maintain the set speed when the cruise control system is operating.

The throttle valve control motor takes the place of the cruise control actuator.

Traction Control System (TCS) Function

If wheel spin occurs during acceleration or cornering, the TCS control unit requests the ECM to reduce the engine power

by retarding the ignition timing and closing the throttle valve. If the wheels lock during deceleration, the TCS control unit

signals the ECM to open the throttle valve.

Engine Protection Function

When the engine speed exceeds 8,000 rpm (M/T) or 7,500 rpm (A/T), the ECM controls the throttle valve, regardless of the

accelerator position, to protect the engine from over-revving.

Fail-safe Function

On this system, the ECM monitors the position of the accelerator pedal with a dual circuit type accelerator position sensor,

and monitors the operation of the throttle valve control motor with a Throttle Position (TP) sensor.

When an abnormality occurs in the system, the ECM restricts the operation of the throttle valve control motor to allow the

engine to continue to run.ProCarManuals.com

Troubleshooting Precautions

ABS Indicator Light:

The ABS indicator light comes on for three seconds and then goes off when the control unit detects no problem during the

initial diagnosis right after the engine starts. The ABS indicator light comes on, and the ABS control unit memorizes the

diagnostic trouble code (DTC) under certain conditions.

• The parking brake is applied for more than 30 seconds while the vehicle is being driven. (DTC 2-1)

• The vehicle loses traction when starting from a stuck condition on a muddy, snowy, or sandy road. (DTC 4-1, 4-2, 4-4, 4-8)

• The vehicle loses traction, and the front wheels spin for more than one minute when starting from a stuck condition on

a muddy, snowy, or sandy road. (DTC 4-8)

• Tire adhesion is lost due to excessive cornering speed. (DTC 5, 5-4, 5-8)

• The vehicle is interfered by strong radio waves (noise), for example, illegal radio, etc. (DTC 8-2)

NOTE: If there is any trouble in the system, the ABS indicator light comes on during driving.

Diagnostic Trouble Code (DTC):

• When the control unit detects a problem and the ABS indicator light comes on, the control unit memorizes the DTC.

• The control unit has three memory registers. When a problem occurs, the control unit stores the DTC in the first memory

register.

• The most recent DTC is indicated first, and the oldest DTC is indicated last.

• The DTCs are erased from the control unit when the ABS control unit +B2 power supply or connector is disconnected.

• The control unit's memory can be erased by disconnecting the ABS 2, 3 fuse for more than three seconds.

Self-diagnosis:

• There are two self-diagnoses described below.

Initial diagnosis: Performed right after the engine starts until the ABS indicator light goes off.

Regular diagnosis: Continuously performed (under some conditions) after the ABS indicator light goes off until the

engine stops.

• The CPU (central processing unit) controls the following when it detects a problem during self-diagnosis:

Turns the ABS indicator light ON.

Turns the front and rear fail-safe relays off.

Stops the ABS control.

Stops the ABS pump.

After the DTC is stored in the control unit, the CPU stops self-diagnosis.ProCarManuals.com

Outline
System Description

Role of System

The NSX/NSX-T traction control is a variable system designed to enhance traction during acceleration and cornering. It

does so by determining the optimum amount of wheel spin for any given driving situation, then suppressing surplus

engine power accordingly.

This version of TCS has a lateral acceleration (Lg) sensor and a deceleration control function to improve traction control

during acceleration and deceleration while cornering. When downshifting quickly to a very low gear on a slippery surface,

the driving wheels tend to slip because of engine braking, resulting in lower directional stability. To counteract this, the

deceleration control function controls engine braking with the TCS control unit.

Construction and Function

The TCS control unit gets signals about the vehicle's speed, direction, and road conditions from sensors at the wheels and

the steering column. Based on these signals, the control unit will determine the optimum amount of wheel spin. Because

the system is variable, the control unit may determine, depending on the driving conditions, that some wheel spin is bene-

ficial (thus enhancing straight-line acceleration), or that no wheel spin is beneficial (thus enhancing cornering). For any

given driving situation, the control unit will determine the amount of wheel spin best suited to the driver's needs and, if

necessary, will then signal the throttle actuator and Engine Control Module (ECM) to reduce engine power.

The system is automatically "ready" whenever the engine is started, but can be manually canceled with the TCS switch.

However, once activated, the system cannot be canceled until it is once again in the ready state.

Components:

• Wheel sensors: The TCS "shares" the wheel sensors with the ABS. The wheel sensors transmit wheel speed signals to

the TCS through the ABS control unit.

• Steering angle sensor: The steering angle sensor signals the TCS control unit about the amount of steering angle.

• Lateral acceleration (Lg) sensor: The Lg sensor detects the lateral acceleration of the vehicle and signals the TCS con-

trol unit.

• TCS control unit: The TCS control unit detects the driving condition signals from the sensors and, if necessary, signals

the throttle actuator and the Engine Control Module (ECM). This version has a lateral acceleration (Lg) sensor, which

improves the traction control performance during cornering.

• Throttle actuator: The throttle actuator opens and closes the throttle valve according to the traction control signal from

the Engine Control Module (ECM).ProCarManuals.com

Construction and Function

TCS Control unit

Acceleration Control

When the drive wheel speed exceeds the vehicle speed by a given amount, the TCS control unit judges that the drive

wheels are slipping, and it outputs the traction control signal to reduce engine power.

Deceleration Control

When the drive wheel speed drops below the vehicle speed by a given amount, the TCS control unit judges that the drive

wheels are slipping, and it outputs the traction control signal to control engine braking properly.

Handling Control

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

(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 lateral acceleration, 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.ProCarManuals.com

Construction and Function (cont'd)
System Description

Fail-Safe Function

If the control unit detects an abnormality, it shuts the

traction control system off and causes the TCS indicator

light to come on. However if the abnormality is detected

while the TCS is activated, the control unit first estab-

lishes 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

indicator light when the Service Check connector termi-

nals are connected with the SCS service connector.

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 gener-

ates waves in the "MR" elements. These waves are

amplified and converted into signals which the control

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 deter-

mines whether traction control is required.ProCarManuals.com