Dynamic Stability Control (DSC) / Traction Control System (TCS) & Hill Launch Assist (HLA)

Go directly to:     Hill Launch Assist

dsc

Portions of the article courtesy of Mazda: DSC MX-5

Mazda’s Dynamic Stability Control system (DSC) automatically takes control of the vehicle when skidding is detected.  The system guards against skidding by optimally controlling engine output and the braking force applied to each wheel through the combined control of the 4-wheel antilock braking system (ABS) and the Traction Control System (TCS).  This helps the vehicle maintain stability even in situations such as when cornering on slippery roads or when steering suddenly to avoid hazards.

Sensors in the vehicle provide speed, steering angle, lateral-G and yaw rate data for both systems, and the performance parameters are effected by the Sport mode switch and the LSD in the Abarths.

For example, if the car understeers and tends towards the outside of a corner, engine output is controlled and braking is applied primarily to the inner front wheel according to the degree of the tendency.  As a result, a yaw moment is formed towards the inner side of the vehicle and the understeer tendency is suppressed.

Conversely, if the vehicle oversteers and tends toward the inside of a curve, braking is applied primarily to the outer front wheel according to the degree of the tendency.  As a result, a yaw moment is formed towards the outer side of the vehicle and the oversteer tendency is suppressed.

dsc can do

The two systems work in harmony, and can normally be controlled together with quick presses of the DSC button ⇓ :

index.10

DSC operation is possible at speeds greater than 12 mph (20 km/h), and is normally ON each time the vehicle is started.  TCS is normally in standby mode, but it will activate if, for instance, you attempt to free the vehicle when it is stuck, or drive it out of freshly fallen snow.  Depressing the accelerator will not increase engine power and freeing the vehicle may be difficult.  When this happens, either deactivate both TCS/DSC (short press of the switch), or with a long press (10 seconds+), you can deactivate TCS independently of DSC.

Note that deactivation of DSC is a misnomer though, since the steering safety system remains in readiness mode, and the feature will re-engage itself (although under more extreme parameters).

To Reset DSC: Hold DSC/TCS  button 10 seconds+


Hill Launch Assist

Another somewhat related feature that also utilizes brake control, is Mazda’s Hill Launch Assist (HLA) – intended to eliminate the need to use the hand brake launching forward from a stop while on a hill, by holding the brakes for about 2 additional seconds (if the brake pedal is released first).

I always thought it was intended only for forward uphill launching with manual transmissions, but apparently it also engages when in reverse, and with automatic transmissions as well, as explained in this page from the FCA Performance Institute Service and Maintenance lesson guide.

Unlike DSC/TCS, there is no switch to deactivate this feature, but according to Brian Goodwin, you can unplug the wiring to the transmission housing, should you really feel the need to disable HLA.  arathol has reported that if you engage the parking brake enough to activate the instrument cluster light (1st click that hopefully that hasn’t engaged the brakes into a frictional state), that should also deactivate HLA.

hill launch assist

More from the Mazda Service Manual:

Block diagram

Hydraulic circuit diagram

Operation

  • Hill Launch Assist (HLA) is controlled by the DSC HU/CM. When the input signals from each module meet the operation conditions, the DSC HU/CM maintains the brake fluid pressure when the driver depressed the brake pedal (hold control). When the engine torque increases to the point of enabling the vehicle to move forward by depressing the accelerator pedal (AT vehicles) or depressing the clutch (MT vehicles), the brake fluid pressure is released (release control) according to the engine torque value.
  • In the event that a malfunction occurs in the DSC system during hold control, the DSC HU/CM releases the brake fluid pressure. When the brake fluid is released due to a DSC system malfunction, slow release control or fast release control is performed according to the nature of the malfunction.

NOTE:

  • Hill Launch Assist (HLA) operates during forward and reverse travel (grade on which system operates changes slightly depending on vehicle conditions such as load, tire wear, tire air pressure).
  • Hill Launch Assist (HLA) operates continuously regardless of the DSC OFF switch operation effect.
  • If a malfunction occurs in the parking brake switch or there is an error in the parking brake signal from the instrument cluster, Hill Launch Assist (HLA) does not operate. In this case, the TCS/DSC indicator light are illuminated simultaneously.
  • If a malfunction occurs in the DSC system, Hill Launch Assist (HLA) does not operate.
Hold control
  • Control conditions (all of the following conditions met):
    • All doors are closed
    • Slope of approx. 3 % or more (MT)
    • Slope of approx. 6 % or more (AT)
    • Wheel speed is 0 km/h {0 mph}
    • Parking brake not operated
    • Accelerator pedal not depressed
    • No fail-safe mode is present
    • Upslope: The selector lever position is in the D/M position (AT)
    • Upslope: The shift lever position is in the position other than R (MT)
    • Downslope: The selector/shift lever position is in the R position
    • Brake pedal is depressed
    • Clutch pedal depressed (MT)

NOTE:

  • If the parking brake is operated during hold control, slow release control is executed and the brake fluid pressure is released. After this, if the brake pedal is depressed again and the parking brake is released, the system transitions to hold control again.
  • Control description
    • If all of the control conditions are met, the DSC HU/CM controls the traction control solenoid valves and maintains brake fluid pressure (driver can depress brake pedal more at this time).
    • If the brake pedal is released, brake fluid pressure (hold-pressure stored in memory) is maintained for a maximum of 1.5 s (MT) or 2.0 s (AT).
Release control
  • Control condition
    • After the accelerator pedal is depressed, the required engine torque for accelerating the vehicle on a slope is produced
  • Control description
    • Brake fluid pressure being maintained is lowered depending on produced engine torque.
Slow release control
  • Control condition (one or more of following conditions are met):
    • Parking brake applied
    • Clutch pedal released (MT)
    • DSC HU/CM has malfunction (performs slow release control only if solenoid valve control is available)
    • 1.5 s have elapsed with brake pedal released (MT)
    • 2.0 s have elapsed with brake pedal released (AT)
  • Control description
    • Brake fluid pressure being maintained is lowered within 1.5 s
Fast release control
  • Control condition
    • DSC HU/CM has malfunction and solenoid valve control is not available
  • Control description
    • Brake fluid pressure being maintained is reduced to 0 kPa {0 mmHg, 0 inHg} immediately

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