Range Rover Classic
ELECTRONIC TRACTION CONTROL
1
DESCRIPTION AND OPERATION
ELECTRONIC TRACTION CONTROL - ETC
WABCO, manufacturer of the ABS brake system have
developed a differential braking system, ETC,
available as an extension to ABS. The system
operates on the rear axle only, to prevent loss of
traction where one wheel has more grip than the
other.
The system works by applying the brake to a spinning
rear wheel. This transfers torque to the wheel with the
grip. The brake supplies the torque resistance which
the wheel cannot.
An example of when the system would operate is
where one side of the vehicle is on ice and the other
side on tarmac. ETC will control the spinning rear
wheel.
If both wheels spin the system does not operate, as
braking one wheel will not aid traction.
The system switches itself out at 50 kph (30 mph)
since a vehicle travelling above this speed will not
need ETC.
System operation is smooth and continuous and will
not affect the comfort of the vehicle.
ETC is inhibited when the brakes are applied.
COMPONENTS
As ETC is an extension of the ABS unit it is only
available on ABS equipped vehicles.
ECU - the system uses an extended ABS ECU. The
same ECU is used on both ETC and non ETC
vehicles. If ETC valve block is not connected
electrically the ECU assumes the vehicle does not
have ETC.
Two solenoid valves - similar to ABS control valves,
incorporated in a valve block fitted to the ABS booster.
In case of failure the valve block may be removed
from the booster unit and a new unit fitted.
Brake pipes - three additional brake pipes to the ETC
valve block are required.
ETC Warning light - situated in the instrument
binnacle, the warning light works in three different
ways:
ETC active - The light will illuminate for a minimum of
two seconds or as long as the system is active. In
practice this time will rarely exceed ten seconds. This
warns the driver that traction is becoming limited.
Protection mode - In the unlikely event that the
system remains active continuously for more than
sixty seconds, the system shuts down to protect
brakes and solenoid valves from overheating. The
warning light will flash at half second intervals for a
minimum of ten seconds while ETC is shut down. If
ETC is shut down, but NOT required by conditions,
the light will not flash.
ETC fault - If a fault occurs which disables ETC, the
warning light is constantly illuminated, (even when
there is no wheel spin,) until ignition is switched off.
Bulb check - The light will illuminate for three
seconds when ignition is switched on and ABS/ETC
self checks completed.
USA vehicles - the warning light will NOT be
illuminated as part of warning light bulb check.