Operation

Operation
ABS
The purpose of ABS is to prevent vehicle wheels locking during brake application, thus maintaining vehicle steerability and stability. This allows the vehicle to be steered while the brakes are applied, even under emergency conditions, and to avoid obstacles where there is sufficient space to redirect the vehicle.

WARNING: ABS is an aid to retaining steering control and stability while braking:

^ ABS cannot defy the natural laws of physics acting on the vehicle.
^ ABS will not prevent accidents resulting from excessive cornering speeds, following another vehicle too closely, aquaplaning, etc.
^ The additional control provided by ASS must never be exploited in a dangerous or reckless manner which could jeopardize the safety of driver or other road users.
^ The fitting of ASS does not imply that the vehicle will always stop in a shorter distance.

NOTE: During normal braking the feet of the brake pedal on vehicles equipped with ABS will be the same as that on non ABS vehicles. During anti-lock braking operation the driver will experience feedback in the form of a pulsating brake pedal and solenoid pump motor noise from the ABS modulator.

The anti-lock braking function is automatically enabled whenever the ABS modulator is in the normal braking mode.
While the anti-lock braking function is enabled, if the ABS ECU detects a wheel decelerating faster than the average, indicating it is about to lock, it operates the ABS modulator in the ABS braking mode for the affected wheel.





ABS ECU Connector Pin Details

Traction Control
This feature uses brake intervention to prevent wheel slippage (i.e. wheel speed faster than vehicle reference speed) during attempts to accelerate or on a slippery road surface. This is done by the ECU, which monitors the speed of each wheel. If any wheel is spinning faster than others, brake pressure is applied to that wheel to slow it down, bringing it in line with other wheel speeds, thus providing the optimum traction between the road surface and each vehicle tyre. Traction control will not function with speeds above 50 km/h.
If ETC is required and the brake pedal is not depressed, the ECU starts the re-circulation pump to draw fluid into the system from the master cylinder. Additional valves are required for the purpose of controlling the volumetric flow. The Continental TEVES system uses two additional solenoid valves in each brake circuit. As the pump starts up, the separation valve blocks the delivery line to the master cylinder and diverts the fluid flow to the pump circuit. The changeover, or electric shuttle valves, control fluid flow from the master cylinder and reservoir. Actual wheel control takes place in the same way as ABS via the control of the individual inlet and outlet valves. Excess volumetric flow of the pump is routed via the pressure relief valve, which is integrated into the separation valve on the Continental TEVES system.
The traction control warning lamp is amber in color and is illuminated in the following circumstances/conditions:
^ It illuminates for a minimum of 2 seconds when TC is active or longer if TC is active for longer than 2 seconds
^ During the initialization phase and a following test phase controlled by the microprocessor
^ In the event of TC fault condition
^ Fully 'on' when manual disable TC function is operated
^ Flashing when brakes are hot (over 350°C)
^ When the controller is switched off, for as long as ignition voltage is supplied to the ABS ECU
^ During diagnostics
To allow the vehicle to be tested on two wheel rolling roads there is a feature which allows the ETC function to be disabled. To disable ETC, the brake pedal has to be operated 10 times within 10 seconds of turning the ignition on. When traction control is disabled, the ETC warning lamp will be illuminated in the instrument pack and no wheel braking will occur during this period. Also, the road speed signal will be an average of the two rotating wheels and no ABS sensor or accelerometer faults will be registered during this period.
The ETC function can be re-enabled at the start of a subsequent ignition cycle by again operating the brake pedal 10 times within 10 seconds of turning the ignition on. Alternatively, the ABS ECU will automatically re-enable the ETC function when it receives a 4.4 mph (7 km/h) speed signal from all four ABS sensors.
Should the ETC (or HDC) be active for long periods the temperature of the brakes may cause damage to the brake components (disks, drums, pads and shoes). To prevent this there is a safety feature that disables the ETC or HDC if it considers the system is overheating. The system functions by the ABS calculating the brake temperature. When the first temperature limit (350°C) is reached the ETC warning lamp will start to flash (if HDC is also 'ON' then the HDC fault lamp will also flash). When the second temperature limit (400°C) has been reached the warning lights will continue to flash but the ETC and HDC functionality will become inactive. Should HDC be active as the second temperature limit is reached the HDC will fade out gradually. System functionality will return when the brakes have returned to the third limit (300°C).

Hill Descent Control
This feature allows the vehicle speed to be controlled during a hill descent using the vehicle Brakes. This feature has to be selected using the Hill descent switch with the selected gear being 'first' or 'reverse' and the brakes below 350°C.
When HDC is selected by operating the latching HDC switch, the HDC information warning lamp is illuminated continuously to indicate HDC is available. If conditions are not met to enable HDC operation, after the switch is operated, the warning lamp flashes. When going downhill and HDC is selected the vehicle will maintain a target speed by applying the brakes. The target speed will be relative to the throttle pedal position. If the slope is not steep enough and the speed is less than the target speed, the vehicle will not accelerate to reach the target speed. The HDC function is brakes intervention only.
Minimum target speeds with the throttle closed are 6 mph (9.6 km/h) in first gear and 4 mph (6.5 km/h) in reverse gear. The first gear target speed is decreased to 4.4 mph (7 km/h) if rough terrain or sharp bends (detected from ABS sensor inputs) are encountered while already traveling at the minimum target speed. Minimum target speeds are increased at cold idle to prevent conflict between the brakes and the engine caused by HDC trying to impose a lower vehicle speed than is normal for the increased engine speeds at cold idle. Minimum target speeds at cold idle are 7.5 mph (12 km/h) in first gear and 4.4 mph (7 km/h) in reverse gear.
During active braking, the brakes are operated in axle pairs on one or both axles. The braking effort is distributed between the front and rear axles as necessary to maintain vehicle stability. Distribution of the braking effort is dependant on direction of travel and braking effort being applied. To prevent wheel lock, anti-lock braking is also enabled during active braking.
The ABS ECU incorporates a fade out strategy that, if a fault occurs or HDC is deselected during active braking, provides a safe transition from active braking to brakes off. The fade out strategy increases the target speed at a low constant acceleration rate, independent of actual throttle position. If active braking is in operation, this causes the braking effort to be gradually reduced and then discontinued. The HDC information warning lamp flashes while fade out is in progress.
If the clutch is disengaged during active braking, the HDC information warning lamp flashes after a delay of 3 seconds. After 60 seconds, if the clutch is still disengaged, the HDC fault warning lamp flashes and active braking operation fades out.
To prevent the brakes overheating, the ABS ECU monitors the amount of active braking employed and, from this, calculates brake temperature. If the ABS ECU determines brake temperature has exceeded a preset limit, it extinguishes the HDC information warning lamp and flashes the HDC fault warning lamp to indicate that HDC should be deselected. If active braking continues and the ABS ECU determines that brake temperature has increased a further 50°C, it fades out active braking and disables HDC. After fade out, the HDC fault warning lamp continues to flash, while HDC is selected, until the ABS ECU calculates brake temperature to be at an acceptable level. This calculation continues even if the ignition is turned off, so turning the ignition off and back on will not reduce the disabled time. When the ABS ECU calculates the brake temperature to be acceptable, it extinguishes the HDC fault warning lamp and illuminates the HDC information warning lamp to indicate HDC is available again. The disabled time is dependant on vehicle speed.

Diagnostics
While the ignition is on, the diagnostics function of the ABS ECU monitors the system for faults. In addition, the return pump is tested by pulsing it briefly immediately after the engine starts provided vehicle speed exceeded 4.4 mph (7 km/h) during the previous ignition cycle. If a fault is detected at any time, the ABS ECU stores a related fault code in memory and illuminates the appropriate warning lamps in the instrument pack. If a fault exists in a warning lamp circuit, the lamp will not illuminate during the lamp check at ignition on, but, provided there are no other faults, the related function will otherwise be fully operational.









Checks Performed By Diagnostics

Electrical Data





Component resistance and voltage values are detailed below:





ABS System Failure Warning Lamps