It's the EBD kicking in ....
EBD
The EBD function optimises the distribution of hydraulic pressure between the front and rear axles, under all vehicle
load configurations and road conditions, to maintain vehicle stability during braking. EBD operates in forward and
reverse and is automatically enabled whenever the ABS modulator is in the normal braking mode at vehicle
deceleration rates of 0.3 g and above (i.e. medium to high brake pedal loads). EBD operation is similar to that of ABS,
but is calibrated to intervene at lower wheel slip limits and operates the brakes in axle pairs instead of individually.
During braking, if the SLABS ECU detects the wheels of one axle going slower than those of the other axle, i.e. a
potential wheel slip situation, it signals the ABS modulator to close the inlet solenoid valve for the brakes of the slower
wheels. This prevents any further increase in hydraulic pressure to those brakes, while allowing the hydraulic pressure
to the brakes on the other axle to increase and so maximise the overall braking effort. If the wheel speeds of the axle
being subjected to EBD control return within the calibrated wheel slip limits, the SLABS ECU signals a stepped
opening of the inlet solenoid valves, which allows a progressive increase of hydraulic pressure to the related brakes.
Operation of EBD is detectable from a stiffening of brake pedal movement as the inlet solenoid valves close and a
slight pulsing of the brake pedal as the inlet solenoid valves open. EBD operation ceases immediately the brake pedal
is released.
The wheel slip limit for EBD operation varies with vehicle speed. During normal operation, the inlet solenoid valves
always operate in axle pairs, with only one axle pair closed at any one time. Since the most lightly loaded wheel during
a braking manoeuvre will usually be the first to reach the slip limit, under most vehicle load configurations and road
conditions EBD control occurs on the trailing axle. However, EBD control can occur on the leading axle or switch
between axles during the braking manoeuvre.
make sure the tyre pressures are even per axle and as close as possible to the standard recommended pressure cos the system was calibrated for that from factory, are they worn the same? i hope they are at least all the same brand... the EBD can be very sensitive if tyres are differently worn or not inflated even, also if one sensor is reading different than the others albeit is within accepted limits it will disturb the system as well so can different than std dimension tyres, it differs fom one vehicle to another depending on sensor's outputs. ... if these things are ruled out nd still no joy you\ll have to plug in a tester and see live sensor inputs or at least measure theyr's resistance and if you see big differencies(above 100 ohm) there's the trouble
untill you fix it remove the ABS relay(R10) to be on the safe side cos it can be dangerous... you'll get the 3 amigos but you'll have normaly operating hydraulic brakes without ABS system involvment
