Lotus Elise / Lotus Exige. Manual - part 61

 

   Lotus Service Notes                                  Section JJ

Page 26

Pressure Increase (Re-apply)

As soon as imminent wheel lock is detected by the ECM, and the ABS control system is activated, the

pump motor is energised.  When the dump valve is opened, and fluid is allowed to bleed off from the wheel
brake circuit into the low pressure accumulator, this fluid is scavenged by the pump and returned back into the
input circuit through an attenuator orifice.  This action is the origin of the 'pedal pushing back' sensation felt by
the driver, with the pressure pulsations from the pump damped and quietened by the restriction of the orifice.
When wheel speed has been restored and the brake pressure is required to increase, the isolation valve is
momentarily opened, to allow master cylinder/pump pressure to raise the pressure in the wheel brake circuit in
increments.  If imminent locking is again sensed, the isolation valve closes, the dump valve opens and the
cycle repeats, with the whole process occuring several times a second.

Isolation valve
pulsed open

Increasing
pressure
to LHF
brake

Inlet from
master
cylinder

Attenuator

Pump

orifice

operating

Accumulator
discharges into
pump

                  j149d

   Lotus Service Notes

                Section JJ

Page 27

Brake Release

When no further wheel locking is sensed by the ECM, the ABS becomes inactive with the isolation valve

open (solenoid de-energised) to allow direct communication between the master cylinder and wheel brake
circuit, and the dump valve closed (solenoid de-energised) to seal off the pressure relief circuit.  The pump will
remain running for a short time to help drain any fluid from the accumulator, whose piston is returned to its start
position under the action of the spring, and return the fluid to the master cylinder reservoir.

Isolation valve
de-energised
and open

Output
to LHF
brake

Inlet from
master
cylinder

Pump runs
for short
period

Fluid scavenged from
low pressure accumulator

      j149e

 

   Lotus Service Notes                                  Section JJ

Page 28

JJ.13 - ELECTRO-HYDRAULIC UNIT

The electro-hydraulic unit is located on the driver's side in the front services compartment, and is flexibly

mounted in a support frame via three isolator rubber bushes.  The support frame itself is fixed to the front
suspension damper top mounting bracket and windscreen frame butress via another three rubber bobbins.  A
single 27 pin electrical connector plug is provided with a sliding retainer to aid its mating with the vehicle
harness.

CAUTION: Do not disconnect or connect the main connector plug with the ignition switched on.  Switch
off the ignition and disconnect the main connector plug before carrying out any electrical welding operations on
the car.

Hydraulic pipe connections to the unit comprise two input pipes from the master cylinder (one for the front

circuit, one for the rear) and four output pipes, one for each of the wheel brakes.  Note that all hydraulic
connections are identified by engraved markings on the unit, with further protection against incorrect connec-
tion provided by the use of two different brake pipe union sizes: M10 x 1.0 and M12 x 1.0.

To Remove Electro-Hydraulic Unit

When removing the unit, beware of dripping brake fluid and take appropriate precautions to prevent

damage to paintwork.
1.

Remove the driver's side front access panel, radiator outlet louvre and wheelarch liner.

2.

Switch off the ignition before drawing out the retainer slide from the connector plug to release the harness
from the unit.

3.

Label each of the hydraulic pipes before disconnecting from the unit and immediately capping the pipes
and plugging the ports to reduce the spillage of brake fluid, and to prevent the ingress of dirt.

4.

Release the three fixings securing the controller mounting bracket to the damper bracket and windscreen
frame butress, and withdraw the unit and mounting cradle.

5.

To remove the controller from the cradle, unscrew the two socket head pins supporting the sides of the
unit, and withdraw the unit from the third grommet at the end of the motor casing.

Mounting
grommet

Mounting
bobbin

Electro-

Controller

hydraulic

mounting

unit

bracket

Socket
head pin

Damper bracket

         j190

   Lotus Service Notes

                Section JJ

Page 29

6.

To refit, reverse the removal procedure, tightening the two socket head mounting pins to 9 Nm, and the
brake pipe unions (both sizes) to 16 Nm, taking care to connect the brake pipes to the correct ports on the
hydraulic block - see diagram.  Press in the retainer slide to connect the harness plug.

7.

Bleed the unit using the procedure detailed in sub-section JJ.3.

8.

Verify correct connection by using the 'Lotus Scan' tool in actuator tests with the car on a wheel free lift.
Check that operation of each solenoid valve affects the appropriate wheel.

Service Breakdown of Electro-Hydraulic Unit

Service parts for this unit are limited to; the hydraulic modulator with pump motor; and the coil integrated

module which comprises the ECM and solenoid pack.

To separate the module from the hydraulic block, release the 'Torx' screws and withdraw the module from

the solenoid valve spigots.  When refitting, check that the gasket is correctly located around the solenoid coil
cluster, before mating with the hydraulic block and fitting the screws.
Note that component parts are calibrated specifically for the Lotus Elise.  Do not use parts from other sources.

JJ.14 - WHEEL SPEED SENSORS

A wheel speed sensor is integrated into each of the four hub bearing assemblies and supplies a signal to

the ABS control module.  The module outputs a road speed signal to the engine ECM, and also to the instru-
ment pack for speedometer operation.

Output from each wheelspeed sensor can be checked using the Scan 2 tool, and if found to be faulty or

absent, the complete hub assembly should be renewed - refer to sub-section CI.5 (front) or DH.4 (rear).

JJ.15 - DATA LINK CONNECTOR (DLC)

The Data Link Connector (DLC) is a 16 terminal elec-

trical connector plug, complying with SAE J 1962, which
provides a means of communication with the ABS and en-
gine management electronic control units.  The connector
is used in service to connect electronic diagnostic equip-
ment such as the 'Lotus Scan' hand held scanner tool which
allows system interrogation including the reading of trou-
ble codes.

The DLC is either tied to the main harness at the front

of the passenger footwell, or secured to the centre under-
side of the scuttle beam.

Data Link
Connector

         em235

RH rear

    LH rear     RH front

LH front

MC rear

MC front

Hydraulic

Master

control

cylinder

unit

         j192