TCS symbol

What is traction control system?

All you need to know about: Traction control system (TCS)

Traction Control System (TCS) is an additional add-on feature on the anti-lock brake systems (ABS) found in most modern vehicles. Traction control is important in improving traction while driving on wet or muddy surfaces, or regulating the speed of the spinning wheels to maintain grip.

Traction control applies brakes on the drive wheel spinning faster compared to the other wheels resulting in the reduction of the engine torque.

ABS and TCS are often used interchangeably to mean the same, however, the two are different in functionality; ABS is activated when sudden braking is applied at high speed while TCS comes to play while driving below the speed of 30 MPH or 48 KM/hr.

The TCS sensors are attached to the ABS for monitoring the speed of the spinning wheel/s. When the sensors detect wheel/s spinning faster, brakes are applied automatically to the wheel/s; Other traction control systems impact on the engine performance through regulating the spark plugs or fuel supply to the engine. This in a way reduces the power relayed to the spinning wheels by restoring balanced power equally.

How to activate and de-activate the TCS

Some drivers may find the intervention of traction control annoying, especially if they drive a performance vehicle. So, most TCS have a button or switch that allows the driver to temporarily deactivate traction control. When the system is disabled, a warning light will illuminate to remind the driver traction control is not available. The system will remain disabled until the driver pushes the TCS button again, or until the start of the next ignition cycle (the default mode for TCS is usually ON).

TCS dashboard symbol
TCS dashboard symbol

Note: While disabling traction control does not disable or affect the operation of the ABS, ABS remain on at all times unless it has disabled itself due to an internal fault.

Most traction control systems are activated at speeds below 30 MPH or 48 KM/Hr. Traction control is also part of a total stability control system that monitors vehicle stability and handling at all speeds.

How to diagnosis traction control problems

The traction control system has its warning light and shares its internal self-diagnostics with the ABS. If a fault occurs in any of the components that affect the operation of either system, one or both warning lights will come on and a diagnostic trouble code (DTC) will be set in the control module that corresponds to the fault(s). If the TCS or ABS warning lights are on, one or both systems are usually disabled and will remain offline until the fault is diagnosed and repaired.

The procedure for reading and clearing TCS/ABS fault codes will vary depending on the vehicle model year and system. On older vehicles and some imports (Acura, Ford for example), the TCS/ABS module has manual flash codes and no scan tool is needed. On most newer applications, though, a scan tool is needed.

TCS/ABS diagnostics requires a scan tool with software that can talk to the TCS/ABS module or body control module (depending on how the vehicle is wired). The scan tool must also be CAN-compliant if the vehicle is a newer one with a Controller Area Network (CAN).

On most applications, the TCS/ABS will have several self-tests that can be run through the scan tool. This includes tests that operate the pump and tests for the TCS/ABS solenoids. Some of these tests may only be available with an OEM factory scan tool.

If any of the hydraulic components in the ABS or brake system are being replaced, a scan tool may also be needed to cycle the ABS solenoids so air can be bled out of the modulator and brake lines.

For specific service procedures, always refer to the vehicle manufacturer service literature. This includes bleeding sequences, wiring diagrams, wheel speed sensor resistance specifications, and component test and replacement procedures.

Warning: The high-pressure accumulator on TCS/ABS systems must be fully depressurized before working on the brakes or opening any brake lines. The brake pedal is pumped 30 to 40 times while the ignition off.

Most traction control problems that occur are related to the loss of a signal from a wheel speed sensor, a pump that fails to run, or a high-pressure accumulator that leaks or can’t hold pressure.

The wheel speeds’ sensors resistance is measured with an ohmmeter device and obtained results compared to specifications. Sensors are magnetic and may not produce a good signal if the tip is contaminated with metallic debris or the air gap between the sensor tip and tone ring is too large.

If a code indicates the high-pressure pump isn’t working, the underlying cause may be a faulty pump relay or a bad wiring connection. If the pump fails to run when the relay is bypassed with a fused jumper wire, the pump has failed and needs to be replaced.

A code that indicates the system is not holding pressure usually means the high-pressure accumulator is leaking (check the seal between the accumulator and modulator/pump assembly, or that the rubber diaphragm inside has ruptured allowing the accumulator to lose its nitrogen gas charge (replace the accumulator after depressurizing the system).

Problems may also occur with any of the solenoid valves in the TCS/ABS modulator assembly. The problem may be mechanical (failure due to rust or corrosion in the valve) or electrical (failure of the solenoid). On most systems, the valves cannot be replaced separately so the entire modulator must be replaced as a unit.

If a code indicates an internal module fault, the TCS/ABS module can usually be replaced as a separate item. It may be attached to the modulator assembly or located elsewhere in the vehicle. Communication errors between the TCS/ABS module and PCM or BCM (Body Control Module) may be the result of a wiring fault.

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