Traction Control System

The Traction Control System significantly reduces the work required from the driver during standing starts and rapid acceleration on slippery road surfaces and during cornering operations at high speeds. An overview of TCS construction and operation will help you understand the TCS troubleshooting method when you study it later.

Traction Control System Introduction

As its name implies, the traction control system (TCS) controls the torque that is transmitted by the tires to the road surface. TCSs used in Honda vehicles are largely classified into two types:

  • Engine output control type
  • Braking control type
By minimizing excessive wheelspin, this operation maximizes the efficiency with which torque reaches the road surface. TCS operation takes place under the following conditions:
  • On slippery road surfaces such as a snow-covered road, the driver of a non-Traction Control System equipped vehicle has to control the accelerator pedal with small, precise movements to prevent wheelspin. TCS performs these control operations automatically to ensure that the vehicle starts moving smoothly.
  • If the output of a non-TCS-controlled engine is too high during a cornering operation, the tires can lose their grip. (The level of grip varies in accordance with the road surface.) The resulting wheelspin prevents torque from being transmitted efficiently to the road, and with a front-wheel-drive vehicle it causes the vehicle to move outward from the driver’s intended cornering line. Under these conditions, TCS performs control functions to keep the vehicle on the driver’s intended cornering line. (The braking control type TCS does not have this function.)

Types of Traction Control System

As mentioned previously, traction control systems are generally classified into one of two independent types – namely, the engine-output control type or the braking control type.

Engine-output Control Type

In a Traction Control System of the engine-output control type, traction is controlled by regulating the engine output. A number of different control methods are available for this purpose, and the system can be further classified into one of three types in accordance with the control method which is used.

In the Acura 2.5TL/Vigor, control signals from the TCS control unit are fed to the powertrain control module (PCM). In accordance with these signals, the PCM controls the engine output by adjusting the fuel injection quantity and ignition timing.

In the Acura 3.5RL/Legend, the Traction Control System control unit transmits signals to a TCS control valve actuator, which closes a TCS control valve that is fitted before the throttle valve. The engine output is thus controlled.

In the NSX, the throttle valve is operated electrically. Signals from the TCS control unit are therefore transmitted to the throttle actuator via the engine control module (ECM). In response to these signals, the throttle actuator closes the throttle valve to control the engine output.

Braking Control Type TCS

A Traction Control System of the braking control type (as implemented in the 1999 Inspire and Acura 3.2 TL) makes use of the components of the anti-skid brake system (ABS). Specifically, if the ABS/ TCS control unit determines that one or both of the front wheels are currently spinning, it performs control of the ABS/TCS modulator unit and applies the brakes to the spinning wheel or wheels.

Major Components of Engine Output Control Type TCS

Engine output control type TCS consists basically of the following components:
  • TCS Control unit
  • TCS switch
  • Wheel speed sensor
  • Steering angle sensor
  • TCS warning lamp
  • TCS control valve (certain models only)
  1. TCS control valve sensor
  2. ABS control unit
  3. Service check connector (2P)
  4. Powertrain control module (PCM)
  5. Steering angle sensor
  6. Right-real wheel sensor
  7. TCS control unit
  8. Left-rear wheel sensor
  9. TCS/Cruise switch
  10. Left-front wheel sensor
  11. TCS control valve actuator
  12. Right-front wheel sensor

Traction Control System Control Unit 

In accordance with signals from the wheel speed sensors and steering angle sensor, the TCS control unit calculates the extent to which the engine output must be controlled and sends appropriate control signals to the ECM. The ECM restricts the engine output accordingly.

The TCS control unit also has the following function:

TCS Self-diagnosis/fail-safe Function

The TCS control unit constantly performs self-diagnostic checks. In the event of an abnormality in the system, it turns on the Traction Control System indicator light and renders the system inactive. If the system is performing a control function when the abnormality is detected, it becomes inactive when the control function is complete. A DTC corresponding to the abnormality is memorized by the control unit. This information can later be read from the unit’s memory to facilitate fault diagnosis.

TCS Switch

The Traction Control System switch is located on the dashboard and enables the driver to temporarily disable the system. If the system is performing a control function when the switch is operated, it becomes inactive when the control function is complete. After the ignition switch is turned OFF, the TCS becomes operational again when the engine is next started.

Wheel Speed Sensors

The wheel speed sensors are shared by the TCS and ABS circuits. Signals from each of the four sensors are transmitted to the TCS control unit via the ABS control unit. In accordance with these signals, the TCS control unit calculates the current vehicle speed, the speeds of the driven wheels, the vehicle’s cornering direction, and other necessary data.

Steering Angle Sensor

The steering angle sensor is attached to the steering shaft. It detects the steering wheel angle and the direction in which the steering wheel is turned.

TCS Indicator Light

The Traction Control System indicator light is incorporated into the instrument panel and illuminates in the event that an abnormality is detected in the TCS. To facilitate fault diagnosis, the light flashes to indicate the DTC when the SCS coupler (this is located under the dashboard) is shortcircuited.

TCS Control Valve (if equipped)

TCS control valve is a normally-opened butterfly valve and is mounted before the throttle valve. When the TCS operates, the TCS control unit sends signals to the TCS control valve actuator, causing it to close the valve to some degree. The engine output is thus restricted.

Function of Engine Output Control Type TCS

Driving Control (for Standing Starts and Acceleration)

During standing starts and acceleration, TCS control unit effects control in accordance with signals from the wheel speed sensors. With a front-wheel-drive vehicle, the sensors on the front wheels indicate the speed of the driven wheels and the sensors on the rear (nondriven) wheels indicate the vehicle’s actual speed. When the PCM/ECM judges that the driven wheels are slipping, it reduces the engine output.

Handling Control (for Cornering)

During cornering operations, TCS control unit effects control in accordance with signals from the wheel speed sensors and steering angle sensor. TCS control unit infers the vehicle’s actual cornering direction from the speed difference between the rear wheels. Simultaneously, TCS control unit infers the driver’s intended cornering direction in accordance with steering angle sensor signals and the vehicle speed (the average speed of the rear wheels). If there is a large discrepancy between the actual and intended cornering directions (as calculated by TCS control unit), TCS control unit infers that the vehicle is not tracing the driver’s intended line and issues appropriate signals to PCM/ECM. In response, PCM/ECM reduces the engine output to eliminate the discrepancy.

Rough Road Control

During acceleration on gravel and other loose surfaces, slight wheelspin on the driven wheels helps the vehicle to accelerate. TCS control unit infers that the vehicle is traveling on a poor road surface based on variations in the signals issued by each of the four wheel speed sensors. Consequently, TCS control unit relaxes its control over the engine output to allow slight wheelspin.

Grip Control

TCS control unit determines the vehicle’s longitudinal and lateral acceleration rates in accordance with the vehicle speed and other factors, and it uses the calculated data to infer the efficiency with which the tires are gripping the road surface. If the TCS control unit infers a high level of grip, it relaxes its control over the engine output to enhance the vehicle’s performance. (This operation permits a small degree of directional drift.)

NSX TCS

The TCS used in the NSX differs greatly from other types of engine output control type TCS in the following regards:

G-sensor

The NSX system incorporates a G-sensor for determination of the vehicle’s lateral acceleration rate. This arrangement enhances the precision of control operations.

Deceleration Control

If the rear (driven) wheels turn slower than the front (non-driven) wheels, TCS control unit infers that the driven wheels are slipping because of excessive engine braking. TCS control unit therefore instructs the throttle actuator to open the throttle slightly.

  1. Right-front wheel sensor
  2. Under-hood fuse/relay box
  3. ABS control unit
  4. Steering angle sensor
  5. Engine control module (ECM)
  6. Right-rear wheel sensor
  7. Transmission control module (TCM)
  8. Throttle body
  9. Throttle actuator
  10. Left-rear wheel sensor
  11. TCS control unit
  12. Lateral acceleration (Lg) sensor
  13. A/T gear position switch
  14. Under-dash fuse box
  15. Left-front wheel sensor
  16. TCS switch

Major Components of Braking Control Type TCS

  1. Under-hood fuse/relay box
  2. Passenger’s under-dash fuse/relay box
  3. Driver’s under-dash fuse/relay box
  4. Right-rear wheel sensor
  5. Left-rear wheel sensor
  6. TCS switch
  7. Data link connector (16P)
  8. Left-front wheel sensor
  9. ABS/TCS control unit
  10. Under-hood ABS relay box Pump motor relay Fail-safe relay TCS relay
  11. Right-front wheel sensor
  12. Modulator unit

Function of Braking Control Type TCS

Traction Control System control unit monitors inputs from the four wheel speed sensors and from PCM when starting from a stop or at low speeds (less than 40 km/h). If it detects that a front wheel speed is significantly higher than the other wheels, it calculates a target front wheel speed. (It is 3 to 10% (depending on the vehicle speed) higher than the rear wheel speed because the tire generates maximum traction at a small slip ratio.)

TCS control unit then operates modulator unit to apply the brake to the spinning wheel. In a low traction situation, such as one front wheel is standstill and the other spins freely, Traction Control System function acts like a limited slip differential. As it brakes the spinning wheel, the differential transfers the torque to the other front wheel, and the vehicle is able to start and accelerate smoothly.

  1. Right front wheel spins on low traction surface
  2. TCS applies braking force to the right front caliper
  3. Differential transfers torque to left front wheel
  4. The car accelerates using the tire on the high traction surface

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